G banding: A special staining technique for
chromosomes that results in alongitudinal differentiation by Giemsa stain,
which is a complex of stains specificfor the phosphate groups of DNA; the
characteristic bands produced are calledG bands; these bands are generally
produced in AT-rich heterochromatic regions
Gain-of-Function Mutation. A mutation
that results in a new functional ability for aprotein, detectable at the
phenotypic level.
Gamete Selection. A modification
of early testing. It involves crossing a good inbredline with a random sample
of pollen from an open-pollinated variety followed byadvancement of superior F1
from selfed seeds on the basis of test cross performance.This leads to
improvement in the existing inbred lines.
Gamete. A cell of meiotic
origin specialized for fertilization. It carries only one memberof a
chromosome/gene pair (in basically diploid individuals). It fuses with
any othersuch cell from the opposite sex or mating type to form a diploid
zygote. It may be anegg cell or a sperm cell.
Gamete: A specialised haploid cell whose
nucleus and often cytoplasm fuseswith that of another gamete in the process of
fertilisation, thus forming a diploidzygote
Gamete: Mature male or female reproductive
cell (sperm orovum) with a haploid set of chromosomes).
Gametic (phase) disequilibrium: In relation to any two loci, the
occurrence ofgametes with a frequency greater than or less than the product of
the frequency ofthe two relevant alleles
Gametic (phase) equilibrium: In relation to any two loci, the
occurrence ofgametes with a frequency equal to the product of the frequency of
the two relevantalleles, Eg. loci A and B are in linkage
equilibrium if the frequency of the gameteAnBn equals the product
of the frequencies of alleles An and Bn
Gametic Frequency. The frequency
of a particular kind of gamete in the population. Allthe three parameters, viz.,
gene frequency, genotypic frequency and gameticfrequency, are used to describe
genetic variation at a locus (loci).
Gametic Number. The number of
chromosomes present in the gametic cell of a species.It is usually designated
by n. It may differ from the basic number (x). In a species
thatis basically diploid, both n and x are equal. However, in a
ployploid, the gametic orhaploid number depends upon the number of basic sets (x)
in the somatic cell. Forexample, in H. vulgare n is equal to x,
but in T. aestivum n amounts to 3x.
Gametic Selection. Selection
against a genotype occurring in gametes (haploids). Ofcourse, there is no
difference between dominant and recessive genes, since bothgenotypes are
phenotypically expressed. Meiotic drive or segregation distortion maybe
considered as one form of gametic selection in which gametes carrying a
particulargene show preferential survival.
Gametic selection: The influences acting to cause
differential reproductivesuccess of one allele over another in a heterozygote
Gametocide: A chemical agent used to selectively
kill either male or femalegametes; it is used in hybrid seed production of
autogamous crops (Eg. barley orwheat)
Gametoclonal variation: Variation among regenerants obtained
from pollenand/or anther culture
Gametocyte. The germ cell.
Gametogamy. The union of
female and male gametes and the fusion of the gamete nucleito form the zygote;
also see fertilisation.
Gametogenesis. The formation
of female and male gametes (sex cells). Oogenesis andspermatogenesis refer to
the formation of egg cell and sperm cell, respectively.
Gametophyte. The haploid
gamete-producing stage in the life cycle of plants. It isprominent and
independent in some species, but reduced or parasitic in others.
Gametophytic Incompatibility. A mating system in which incompatibility reaction isgoverned by the
genetic constitution of the male gametes. It is also calledoppositional-factor
system because stylar tissues prohibit or slow down the growth ofpollen-tube
containing the same allele of the incompatibility gene. Althoughcontrolled by
one gene with multiple alleles (Nicotiana spp.), two-loci system hasalso
been found (e.g., rye).
Gametophytic self-incompatibility: Self-incompatibility is based on
thegenotypic and phenotypic relationship between the female and male
reproductivesystem; alleles in cells of the pistil determine its receptivity to
pollen; the phenotypeof the pollen, expressed as its inability to effect
fertilization, may be determined byits own alleles, referred to as gametophytic
incompatibility
GATT (1948). A convention
called General Agreement on Trade and Tariffs. It was setup in January
01, 1948 to regulate the world trade of goods. Now more than 108countries,
including India are the members of this convention. Later on, it wasreplaced
byWTO.
GC clampA stretch of ~30 bp containing only GC
bases; used at the 50 end of a primer in case of D/TGGE.
GD-based clustering methodsClustering based
on a pairwise distance matrix.
Gene (DNA) sequencing: Determining the exact sequence of
nucleotide basesin a strand of DNA to better understand the behavior of a gene.
Gene (Johannsen 1909). The fundamental and functional unit of heredity. In classicalsense, any
inherited factor that determines a biological characteristic of an organism
iscalled a gene. The concept of the gene dates back to 1865 when Gregor
Mendelshowed that certain well-defined attributes of Pisum spp. are
governed independentlyby a number of factors (genes). Biochemically, it is a
segment of DNA, composed ofa transcribed region and a regulatory sequence that
make transcription possible.
Gene Action. The way a
gene(s) acts in producing a particular phenotype. It can be linearor
non-linear.
Gene Amplification. The process by
which the number of copies of a chromosomalsegment is increased in a somatic
cell.
Gene amplification: The more or less specific production
of multiple copies ofa gene
Gene cloning: Insertion of a DNA fragment carrying a
gene into a cloningvector; subsequent propagation of the recombinant DNA
molecule in a hostorganism results in many identical copies of the gene
(clones) in a form that ismore easily accessible than the original chromosomal
copy
Gene cloning: Isolating a gene and making many
copies of itby inserting the DNA sequence into a vector, then into acell, and
allowing the cell to reproduce and make manycopies of the gene.
Gene Conversion. A meiotic
process of directed change in which one allele directs theconversion of a
partner allele into its own form.
Gene conversion: A process in
which a small segment of one chromosome is copied in the place of its
homologous segment of the homologous chromosome during meiosis.
Gene Deployment. A strategy of
resistance management that involves the use of differentsets of resistance
genes in the various sub-areas of an epidemiological unit. In thiscase, the production
area is subdivided into several zones, and each zone is plantedwith a variety
having a specific gene(s) for resistance. It is a planned way to avoidmonoculture
of a particular resistance gene over long geographical areas. This type
ofgeographical gene deployment has been termed geographical multiline by
Nelson(1973). However, gene deployment requires a number of genes with
similareffectiveness for control of prevalent races, and the cooperation
between breeders andpathologists. The absence of major genes with equal
resistance against the prevalentraces limits its feasibility because when one
gene is clearly superior to others, mostbreeders prefer to use it.
Gene discovery: A process whereby the individual base
nucleotides in anorganism’s DNA are identified in order to learn more about the
genome of theorganism, and to learn about or identify specific areas of
interest on chromosomes. This process allows for the identification of specific
genes that code for a particulartrait or traits.
Gene Disruption. Inactivation
of a gene by the integration of a specially engineeredintroduced DNA fragment.
Gene dosage: The number of times a given gene is
present in the nucleus of acell and/or individual
Gene Dose. The number of
copies of a particular gene present in the genome.
Gene duplication: A process in evolution in which a gene
is copied twice; thetwo copies lie side by side along the same chromosome
Gene expression profiling: The analysis of gene expression level
of many genesat the same time; technologies that can be used to obtain this
information includeNorthern blot, DNA chips, high-density array spotted on
glass or membranes, andquantitative techniques
Gene expression: The phenotypic manifestation of a gene
depending onthe different levels of gene activation, or the process by which
the informationin a gene is used to produce a protein; in molecular genetics,
the full use of theinformation in a gene via transcription and
translation leading to production of aprotein and hence the appearance of the
phenotype determined by that gene; geneexpression is assumed to be controlled
at various points in the sequence leadingto protein synthesis; this control is
thought to be the major determinant of cellulardifferentiation
Gene expression: The process in which a cell produces
theprotein, and thus the characteristic, that is specified by agene’s
nucleotide sequence.
Gene families: Groups of closely related genes that
make similar products.
Gene Family. A set of genes
in one genome all descended from the same ancestral gene.
Gene flow: The movement of genes from one
individual or population toanother genetically compatible individual or
population.
Gene Frequency. Also called allele
frequency; the proportion in which different allelesof a gene occur in a
population. The term ‘allelic’ frequency is most appropriate,although used less
frequently. One should properly use the term “allele frequency”;however, the
usage of the term “gene frequency” is too widespread to enable an easychange.
Gene frequency: The number of loci at which a
particular allele is founddivided by the total number of loci at which it could
occur for a given population, expressed as a proportion or percentage
Gene Fusion. The accidental
joining of DNA of two genes (as can occur in atranslocation). It can
give rise to hybrid proteins or to the misregulation of thetranscription unit
of one gene by the cis-regulatory elements (enhancers) of
another.
Gene insertion: The addition of one or more copies of
a normal gene into adefective chromosome
Gene Interaction. Modification
of gene action by a non-allelic gene(s). it may be thecollaboration of several
different genes in the production of one phenotypic character(or related group
of characters).
Gene interaction: Modification of gene action by a
nonallelic gene or genes,generally the interaction between products of
nonallelic genes
Gene library: A collection of DNA fragments
(carried on vectormolecules) that, taken together, represents the total DNA of
a certain cell type or organism.
Gene Map. A linear
designation of mutant sites within a gene, based on the variousfrequencies of
interallelic (intragenic) recombination.
Gene map: A graphic presentation of the linear
arrangement of a chromosome orsegment; it shows the relative distance between
loci gained in linkage experiments
Gene mapping: Determining the relative physical
locations of genes on achromosome. Useful for plant and animal breeding.
Gene Mutation. A point
mutation that results from changes within the structure of agene.
Gene mutation: A heritable change of gene revealed by
phenotypicmodifications
Gene ontology: It describes
features of gene products in multiple species.
Gene Pair. The two copies
of a particular gene present in a diploid cell (one in eachchromosome set).
Gene pool system: it consists of three informal
categories in order to provide agenetic perspective and focus for cultivated
plants
Gene Pool. The sum total
of genes that occur in the reproductive gametes of a population.It can be
considered as a gametic pool from which samples are drawn at random toform the
zygotes of the next generation.
Gene pool: The reservoir of different genes of a
certain plant species or lower andhigher taxa available for crossing and
selection; it may be differentiated between(1) primary gene pools (consists of
those species that readily hybridize, produceviable hybrids, and have
chromosomes that may freely recombine), (2) secondarygene pools (consists of
those species with a certain degree of hybridization barrierdue to ploidy
differences, chromosome alterations, or incompatibility genes),and (3) tertiary
gene pools (consists of distinct species or higher taxa with strongcrossing
barriers); in general, the total number of genes or the amount of
geneticinformation that is possessed by all the reproductive members of a
population ofsexually reproducing organisms
Gene prediction: Identification,
by genome sequence analysis, of genomic regions that function as genes.
Gene product: The biochemical material, either RNA
or protein, resulting fromexpression of a gene. The amount of gene product is
used to measure how active agene is; abnormal amounts can be correlated with
disease-causing alleles.
Gene pyramiding: In general
terms, bringing together two or more genes controlling a single trait in a
single line/variety.
Gene Pyramidying. A strategy for
management of resistance that involves incorporationof an increasing number of
resistance genes into the same cultivars likely to bereleased in succession.
Thus, with the available number of genes, the resistance canbe used for a long
time. However, there are several disadvantages that limit its use:
(a)considerable efforts are required to incorporate many a major gene into
onegenotype, (b) the use of back cross method to incorporate the major genes
into onegenotype restricts the agronomic characteristics of the new cultivar,
and (c) resistanceof the cultivar may encourage evolution of new virulent races
of the pathogen,particularly if the same major genes are used singly in other
varieties being grown inthe adjacent area.
Gene Rearrangement. The process of
programmed changes in the DNA structure of thesomatic cells, leading to changes
in gene number or in the structural and functionalproperties of the rearranged
gene.
Gene regulation: The process of controlling the
synthesis orsuppression of gene products in specific cells or tissues.
Gene Replacement. The insertion
of a genetically engineered transgene in place of aresident gene that is
often achieved by a double crossover.
Gene silencing: The suppression of gene expression,
for example, of the genefor polygalacturonase which causes fruit to ripen, or
the gene for P34 protein insoybeans, via a variety of methods, for
example, via RNA interference (RNAi), chemical genetics, effect of
certain viruses, zinc finger proteins, or sense orantisense genes
Gene space: The fraction of genome that
corresponds to the protein-coding genes and, also, the distribution pattern of
these genes.
Gene space-based association mapping: Association
analysis using SNP data generated from sequences of transcribed genes.
Gene splicing: Joining pieces of DNA from different
sourcesusing recombinant DNA technology.
Gene splicing: The enzymatic attachment ( joining) of
one gene or part of a geneto another; also removal of introns and splicing of
exons during mRNA synthesis
Gene substitution: The replacement of one allele by
another mutant allele in apopulation by natural or directed selection
Gene symbol: various symbols which are used to represent genes or alleles
Gene Tagging. Mapping of
genes of economic importance close to known markers. Thusa (molecular) marker
very closely linked to a gene of interest can act as a tag. This tag(molecular
marker) can be used for indirect selection of the target gene in the100breeding
programme. Several genes of economic importance such as diseaseresistance,
fertility restoration, stress tolerance, insect resistance, yield
attributingtraits, and the like have been tagged. Gene tagging is a
pre-requirement for markerassistedselection and map based gene cloning.
Gene tagging: The labeling of a gene by a marker
gene or specific DNAsequence closely linked
Gene Therapy. The correction
of a genetic deficiency in a cell by the addition of newDNA and its insertion
into the genome.
Gene therapy: Insertion of normal DNA directly into
cells to correct a geneticdefect.
Gene transfer: The physical transfer of a gene by
crossing, chromosomalmanipulation, and molecular means; in biotechnology,
different methods aredescribed, such as (1) microinjection, (2) insertion via
microprojectiles (particlegun, particle bombardment) using silicon fibers
as carriers of the DNA, (3) directtransfer, (4) electroporation, (5) liposome
fusion, or (6) a vector-mediated transfer
Gene translocation: The transfer or movement of a gene or
gene fragment fromone chromosomal location to another; often it alters or
abolishes expression
Gene/QTL introgression: Transfer of the
target gene(s)/QTL(s) into the RP using backcross procedure.
Gene: The fundamental physical and
functional unit of heredity, which carriesinformation from one generation to
the next; a segment of DNA, composed of atranscribed region and a regulatory
sequence that makes transcription possible.
Gene: The fundamental unit of heredity; a bundle
of informationfor a specific biological structure or function.
Genealogy. A record of
the descent of an individual, or a group of individuals, from anancestor or
ancestors (or from older forms).
Genebank: An establishment in which both somatic
and hereditary geneticmaterial are conserved (seeds, pollen, whole plants,
extracted DNA); it stores, ina viable form, material from plants that are in
danger of extinction in the wildand cultivars that are not currently in popular
use; the stored genetic material canbe called up when required; the normal
method of storage is to reduce the watercontent of seed material to around 4%
and keep it at 0°C or less (−20°C); all storedstocks are periodically checked
by germination tests
Gene-based markers: Markers based on
polymorphic sites within genes, but their relationships with the relevant trait
phenotypes are not known. Syn., gene-targeted markers, gene-specific markers.
Gene-for-Gene Hypothesis (Flor 1956). The interaction of gene(s) conditioningresistance in the host with the
gene(s) governing pathogenicity in the pathogen, finallydetermining the disease
expression by the host. Flor (1956) established it in flax inrelation to flax
rust. He found that hybrids between races of flax rust segregate
forpathogenicity in accordance with the number of genes for resistance in the
differentialhost. Thus if a variety is PP, the ratio of avirulent to virulent
segregates in the hybrids95between an avirulent and virulent strains is found
to be 3:1. If the host variety isPPRR (that is, it carries two dominant genes),
the ratio of avirulent to virulent will be15:1, and so on. This suggests that
complementary genic systems in the host andparasite control reaction to the
flax rust. Resistance occurs when complementarygenes in both host and parasite
are dominant; if either or both the pairs ofcomplementary genes are recessive,
susceptibility results. Thus a variety that carriesno dominant genes for
resistance is susceptible to all races of the parasite and avariety carrying
one dominant gene for resistance is resistant to all races carrying thedominant
complementary gene for pathogenicity. The gene-for-gene relationshipprobably
also operates for host-specific insects but not for insects that have
manyhosts. However, the gene-for-gene hypothesis has been criticized on several
grounds;some are: (1) it does not recognize intermediate reaction, and (2) it
does not conveyany idea about the strength of the resistant gene. According to
this hypothesis, foreach gene conditioning resistance in the host, there is a
corresponding gene governingvirulence in the pathogen. Therefore, a minimum of two
resistance genes in the hostand two complementary virulence genes in
the pathogen are necessary to demonstratea gene for gene gene hypothesis. In
addition, the disease reaction as demonstrated byFlor is the most common
pattern observed with biotrophic pathogens. Withpathogens, that produce
host-specific toxins (such as victorin by Drechsleravictoriae),
an opposite pattern is found. Genotype of the host Genotype of the pathogen
Host reactionnnpp ANAN APAP susceptibleNNpp aNaN APAP susceptibleNNpp ANAN APAP
resistantnnPP ANAN aPaP susceptiblennPP ANAN APAP resistantNNPP aNaN aPaP susceptibleNNPP
ANAN APAP resistant96
Gene-for-gene theory: In certain plant-pathogen
interactions, a gene forresistance in the host corresponds to and is directed
against a gene for virulence inthe pathogen; in flowering plants, four families
of disease resistance genes confergene-for-gene resistance to a wide array of
pathogens by recognising the productsof the corresponding pathogen avirulence
genes
General Combining Ability. The
performance of an inbred line in a cross with an openpollinatedvariety. The average
performance of an inbred line in a series of singlecrosses is called average
combining ability. There is a strong correlation betweenperformance of an
inbred in inbred-variety cross and average performance of thesame
inbred in a number of single crosses. Thus the two terms, general and
averagecombining ability are used interchangeably and synonymously. However,
the termgeneral combining ability is used more commonly and frequently than the
latter. GCAis critically important in adaptedness and yield. It results from
additive effects ofmany alleles of many different loci that enhance performance
cumulatively inmultiple environments within a given ecogeographical regions;
thus it is amenable toimprovement by repeated cycles of selection.
General combining ability: The average performance of a strain or
genotypein series of hybrid combinations with other genotypes is termed as
GeneralCombining Ability
General Resistance. Non-specific
host plant resistance.
General resistance: Resistance against all biotypes of a
pathogen; nonspecifichost-plant resistance general, a nontypical form or
function
Generalised lattice design: Each replicate is subdivided into
incomplete blockstypically of 5 or 6 plots; sometimes referred to as “alpha
design” (Patterson and Williams , 1976)
Generation Time. The time
between two successive generations.
Generation. The phase in
the life cycle of plants, which extends from one to theimmediately successive
reproduction (alternation of generation). In genetics and plantbreeding, it
corresponds to whole reproductive cycle, and comprises those individualsof a
population who are equally removed from a common ancestor.
Generative. Reproductive.
Genetic (linkage) map: The linear arrangement of gene loci on
a chromosome,deduced from genetic recombination experiments; a genetic map unit
is defined asthe distance between gene pairs for which one product of meiosis
out of a hundredis recombinant (i.e. it equals a recombination frequency of 1%)
Genetic Advance. The genetic
superiority (and not phenotypic) of selected individuals /lines/families
over the base population. It measures the difference between meangenotypic
values of selected lines (As) and of the original lines (Ao). Thus, Gs = As –Ao
= k × σP × H2. Therefore, it depends on: k = standardized
selection differentialand its value is fixed for a given proportion of lines
saved from the base population(2.06 at 5% selection intensity), σP = phenotypic
standard deviation of the original97population, and H2 = heritability
coefficient (broad sense). However, heritabilitycould be high even when genetic
variance is low; but, genetic advance is high if theestimates of genetic
variance and k are high.
Genetic Assortative Mating. Mating together of individuals more closely related (byancestry) than
individuals mating at random. Genetic assortative mating at all loci iscalled
inbreeding. (Inbreeding deals with the entire genome whereas geneticassortative
mating is specific to a locus). It results in an increase in homozygosity.
Genetic Code. The set of correspondences
between nucleotide pair triplets in DNA andamino acids in polypeptides.
Genetic code: The language in which DNA’s
instructionsare written. The code consists of triplets of nucleotides(codons),
with each triplet corresponding to one amino acidin a protein structure or to a
signal to start or stop proteinproduction.
Genetic code: The set of correspondences between
base triplets in DNA andamino acids in protein; these base triplets carry the
genetic information for proteinsynthesis
Genetic correlation: The correlation between the genotypic
values of twocharacters with respect to the genetic character
Genetic Cost. Also called selection
cost; applies to deleterious recessive genes. It is theloss of fitness per
individuals affected (s) times the frequency of affected
individuals92(q2), that is, selection cost equals to selection coefficient
times frequency ofdeleterious recessive genes (genetic cost = s x q2).
Suppose a population in whichthere are three genotypes (AA, Aa,
and aa) and their fitness are WAA= WAa = 1.0, Waa= 0.8. Let p = q = 0.5,
then genetic cost will be 0.2 x 0.25 = 0.05.
Genetic counseling: Information and support provided by a
specialist doctor,usually a geneticist, to parents who have known conditions in
their families or whoare concerned about the future possibility of genetically
transmitted conditions.
Genetic Death. Expression of
genetic load carried by a population that is accompaniedby the loss of a
portion of its individuals. It is not necessarily an actual death beforereproductive
age but can also be expressed through sterility, inability to find a mate,or by
any means that reduces reproductive ability relative to the optimum
genotype.Numerically it equals to sq2N, where ‘s’ is selection coefficient
against deleterioushomozygote, q2 is the frequency of such homozygotes, and N
is the number ofindividuals in a population.
Genetic Disassortative Mating. Mating between individuals less closely related (byancestry) than the
average. In the broadest sense, it is called outbreeding. Its realapplication
is only in connection with breeding hybrid varieties. Also called negativeassortative
mating.
Genetic Dissection. The process of
identifying a particular biological structure orfunction through the use of
recombination and mutation.
Genetic distanceIn genetic
diversity analysis, a quantitative measure of the genetic difference between
two entities in terms of differences in their DNA sequences, gene frequencies,
etc. In linkage mapping, recombination frequency corrected for the occurrence
of multiple crossovers between the concerned gene/marker pair.
Genetic diversity analysis: Estimation of
genetic similarity (or dissimilarity) between pairs of entities and use of
these estimates for grouping of the entities.
Genetic diversity: The sum total of
genetic differences present among different individuals, genotypes, strains,
clones, or populations of a species.
Genetic Drift. Random
fluctuations in allelic or genotypic frequencies resulting fromsmall population
size.
Genetic drift: Random change in
gene frequency of a population due to random sampling of gametes that unite to
produce the finite number of individuals in each generation.
Genetic drift: The random fluctuations of gene
frequencies in a populationsuch that the genes amongst offspring are not a
perfectly representative samplingof the parental genes
Genetic Engineering. Genetic
manipulation bypassing sexual reproduction so thatindividuals with a new
combination of heritable properties are established. Two toolsof genetic engineering
are rDNA technology and protoplast fusion. Tobacco is thefirst crop, which was
genetically engineered in 1986.
Genetic engineering: Manipulation of an organism’s genes by
introducing,eliminating or rearranging specific genes using the methods of modern
molecularbiology, particularly those techniques referred to as recombinant DNA
techniques.
Genetic engineering: The manipulation of genes,
composedof DNA, to create heritable changes in biological organismsand products
that are useful to people, living things, or theenvironment.
Genetic Enhancement. Also called
genetic improvement; increasing frequency ofdesirable alleles at individual
loci. Several mechanisms such as dominance,overdominance, epistasis, linkage,
and the like may interact towards geneticenhancement in a given genotype. Once
superior genetic make-up is established, itleads to significant increase in
yield. For example, the proportion of yield gain bygrowing single cross hybrids
(from 1960-1990 in USA) resulting from geneticimprovement has been estimated to
be > 60%, whereas < 40% was ascribed toimproved cultural practices,
including increased use of fertilizers.
Genetic Equilibrium. The condition
in which successive generations of a populationcontain the same genotypes in
the same proportions with respect to particular genes orcombinations of genes.
The consequence of such a condition is that mean of thepopulation remains
unchanged owing to constancy of gene and genotypic frequencies.
Genetic equilibrium: An equilibrium in which the frequencies
of two allelesat a given locus are maintained at the same values generation
after generation;a tendency for the population to equilibrate its genetic
composition and resistsudden change is called genetic homoeostasis
Genetic Erosion. The gradual
and persistent loss of plant genetic resources (differentalleles) due to
different processes. This may be the result various breeding methodssuch as
inbreeding. Modern agriculture that follows planting of a few superiorvarieties
may eventually lead to genetic erosion.
Genetic erosion: The loss of genetic diversity caused
by eithernatural or manmade processes.
Genetic erosion: The loss of genetic information that
occurs when highlyadaptable cultivars are developed and threaten the survival
of their more locallyadapted ancestors, which form the genetic base of the crop
Genetic Extinction. See genetic
death.
Genetic Gain. The expected
genetic superiority of the progeny of the selectedindividuals compared to the
base population. If the original population consisted of amixture of pure
lines/clones, the genetic advance predicted on the basis of broadsense heritability
amounts to genetic gain. If, however, the base population consistedof a mixture
of segregating materials, then genetic gain amounts to the geneticadvance based
on narrow sense heritability. Under such a situation, genetic gain is: Gs= k
x σP x h2, whereas, h2 = narrow sense heritability.
Genetic heterogeneity: A similar phenotype being caused by
differentmutations. Most commonly used for a similar phenotype being caused
bymutations in different genes. Allelic heterogeneity refers to different
mutations inthe same gene.
Genetic Homeostasis. The stability
of a group of genotypes (plants) that exceeds that ofits individual members;
also called population buffering. Heterogeneous cultivarsgenerally have
more stability on the average than do homogeneous ones. In genetics,it is the
maintenance of genetic variability in a population in the face of all the
forcesacting to reduce it. Over the long period of evolution in a particular
environment, apopulation has built-up a particular array of gene frequencies,
which confers a veryhigh degree of fitness upon the population. Therefore, any
departure from thesefrequencies may reduce fitness, and thus the population
opposes any change andmaintains such frequencies in it. According to Lerner
(1954), homeostasis may alsoarise from the necessity for the maintenance of
certain level of heterozygosity toensure normal development.
Genetic Homeostasis. The tendency
of a population to maintain its dynamic state ofequilibrium of its gene pool,
which results in optimum balance to the population dueto self-regulatory
mechanisms; also called population buffering or collectivehomeostasis.
Selection leads to disruption of such state; however, relaxation in98selection
pressure results in at least partial restoration of the original
geneticcomposition.
Genetic Inertia. See genetic
homeostasis.
Genetic Information. The sum total
of instructions, which direct all the activities of thecell and are stored in
the nucleotide sequence of nucleic acids (DNA and RNA).
Genetic Isolate. A breeding
population, which does not exchange genes with any othersuch group.
Genetic Load. The proportion
by which fitness of a population at the given locus isdecreased owing to the
presence of deleterious (lethal, semilethal, sub vital) genes. Itis expressed
as the average number of potential genetic deaths per individual. At a94locus,
if the fitness of a genotype (aa) carrying deleterious genes is 1-s, the
incurredgenetic loss is sq2. The value sq2 also equals the mutation rate at
equilibrium. Thereare two principal components of genetic load: mutational
load and segregationalload. The former is the load maintained by
recurrent mutation to deleterious alleles atloci that are homozygous for
non-deleterious alleles. The latter is the load maintainedby segregation from
advantageous heterozygotes.
Genetic load: The average number of lethal mutations
per individual in apopulation
Genetic Male Sterility. A type of male
sterility that is governed by the gene(s) carriedon the chromosomes. The male
sterile condition is ordinarily monogenic recessive. Itsexploitation in hybrid
seed production is rather difficult due to problems involved inthe maintenance
of male-sterile line. Male-sterile stocks are maintained by crossingwith
heterozygous male-fertile line (Ms ms). This necessitates identification of
malesterile(and male-fertile) plants since the progeny contains the two types
in equalproportions. To circumvent this problem, genetic markers such as
tightly linked genesor pleiotropic effects of male-sterile genes can be used.
Genetic map: A schematic representation of
genetic markers in the same order, in which they are located in a chromosome
along with the genetic distances between them.
Genetic mapping: The process of determination of a
genetic map; in formertime, genetic mapping was usually on a gene by gene
basis; until molecularmarkers, there were no specific projects to map entire
genomes; therefore, geneticswill never be the same because of greater precision
(<0.5 cM), fewer crosses, useof F2 data, fewer breeding
generations, more reliance on maps, mapping kits, etc.
Genetic marker locus: The specific
location in a genome identified by a genetic marker.
Genetic marker: A gene or DNA sequence at a known
location on a chromosomethat can be used to identify individuals or species. A
genetic marker may be ashort or long DNA sequence. Some common types of genetic
markers are RFLPs (Restriction Fragment Length Polymorphism), SSLPs (Simple
Sequence LengthPolymorphism), SNPs (Single Nucleotide Polymorphism), and SSRs
(SimpleSequence Repeat DNA marker). Genetic markers play a role in genetic
engineeringbecause they allow breeders to locate and utilize genes of interest
for genetic gains.
Genetic marker: A genetic factor that can be
identified andthus acts to determine the presence of genes or traits linkedwith
it but not easily identified.
Genetic marker: A trait that is
polymorphic, easily and reliably identified, and readily followed in
segregating generations and indicates the genotype of the individuals that
exhibit the trait..
Genetic Markers. Alleles used
as experimental probes to keep track of an individual, atissue, a cell, a
nucleus, a chromosome, or a gene; also see morphological andmolecular
markers.
Genetic Material. A substance
that carries genetic information. For a substance to becalled as the genetic
material, it should: (a) replicate, (b) carry all kinds of necessarybiological
information, (c) transmit these information to the cell, and (d) be
relativelystable. Nucleic acids fulfil all these conditions, and are therefore
called the geneticmaterials.
Genetic Mobility. The ability of
biological species to change their habitat or (in plants)the range of
distribution of pollen and seeds. It largely determines the mannerwhereby the
mechanism of geographical isolation becomes effective.93
Genetic modification: The production of heritable
improvements in plants oranimals for specific uses, via either genetic
engineering or other more traditionalmethods. Some countries other than the
United States use this term to referspecifically to genetic engineering.
Genetic polymorphism: Differences
between DNA sequences.
Genetic Resources. An assembly of
divergent gene complexes that can be exploited toimprove a crop species. Based
on utility, it can be primary, secondary, etc. gene pools.
Genetic stocks: Accessions that typically possess
one or morespecial genetic traits that make them of interest for research.
Genetic Value. A measure of
the inherent potential of a genotype that cannot be assessedexactly. Largely,
differences in the genetic values can be judged by differences inphenotypic
values particularly when environment affects the phenotypes uniformly inthe
same direction.
Genetic Variance. A parameter
which measures genetic differences among individuals/lines/families of a
population. Since all measurements are necessarily made onphenotypes, it is
measured indirectly.
Genetic variance: A portion of phenotypic variance that
results from the varyinggenotypes of the individuals in a population; together
with the environmentalvariance, it adds up to the total phenotypic variance
observed amongst individualsin a population; it is divided into additive and
dominance variance
Genetic vulnerability: The condition that results when a
cropor a plant species is genetically and uniformly susceptible toa pest,
pathogen, or environmental hazard.
Genetic vulnerability: The susceptibility of genetically
uniform crops todamage or destruction caused by outbreaks of a disease or pest
or unusually poorweather conditions or climatic change
Genetic. Of heredity; hereditary.
Genetical genomicsGenetic analyses
of the expression values of genes in the same way as any other phenotype.
Genetically modified (GM) organism: An organism whosegenetic makeup has
been changed by any method includingnatural processes, genetic engineering,
cloning, mutagenesis, or others.
Genetically modified organism (GMO): A plant or animal whose
geneticmaterial (DNA) has been altered through genetic
engineering/biotechnologytechniques (insertion/deletion of genes) to produce a
genotype that possesses amodified trait that is not found in naturally
occurring plants of that species. Whengenes are inserted, they usually come
from a different species. The principle ofproducing a GMO is to add new genetic
material into an organism’s genome.
Genetics (Bateson 1905). The study of heredity and variation. The term has been derivedfrom a
Greek word, which means, “to generate”. It is the study of genes through
theirvariation.Genotypic. Of or concerned with genotype.
Genetics. The study or science of genes and
heredity.
Genetics: Study of the patterns of inheritance
of specific traits.
Genic Hybrid Sterility. Failure to
gamete formation in the hybrid due to abnormaldevelopmental processes caused by
specific gene complexes. In this case, meioticpairing is completely normal;
sterility seems to be caused by incompatibility betweengenes derived from two
parents.
Genocopy. The production
of the same phenotype by different genes.
Genome Analysis. Genetic
dissection of genomes of a cultivated species along withrelated ones. It is
carried out in order to: (a) determine phylogenetic relationshipbetween
species, (b) trace phylogeny of a species, (c) provide a guideline to the
plantbreeders for transferring an alien gene(s) into a commercial cultivar, and
(d) producesynthetic allopolyploid. The criteria that are used in genome
analysis may begeographical distribution, morphology of parents, cytological
and biochemicalcharacteristics, and the like.
Genome annotationIdentification
of genes, their 50- and 30-regulatory sequences, as well as their functions.
Genome mapping: Determining a set of landmarks or
genetic markers–genesor short DNA sequences–in the genome that will enable
researchers to find newgenes. A genome map is one-dimensional–a straight line
with landmarks thatstand for genes or DNA sequences. They guide a researcher
toward a gene that issuspected to be involved in some process that is of
interest.
Genome mutation: Spontaneous or induced changes in the
number of completechromosomes that result either in polyploids or aneuploids
Genome projects: Research and technology development
efforts aimed atmapping and sequencing some or all of the genome of human
beings and otherorganisms.
Genome sequencing: Determining the order of every DNA
base in the genome. More detailed than a genome map and usually done on short
segments of thegenome. Done to establish the distinctive order of genes of an
organism.
Genome Wide Selection. Also called genomic
selection (GS); targeting identification ofsuperior lines with higher
breeding value in a breeding programme based on genomewidemarker profile data.
As breeding values are estimated using the genome widemarker data, these are
generally referred as genomic-estimated breeding values(GEBVs). In brief, GS
employs two populations: (i) ‘training population’, that isgenerally comprised
of breeding lines that were/ are in use in a breeding programmeand phenotyping
data, not for some traits, but for overall performance (e.g., yield andyield
components) are available across the environments, and (ii)
‘candidatepopulation’, which is generally being used currently by breeders.
Genome. A set of chromosomes
usually tending to inherit together as a group. Itcorresponds to the haploid
set in a basically diploid species. Also, the basic number(x) in
a species constitutes a genome. It is the entire complement of genetic
materialin a set of chromosomes.
Genome: The complete set of chromosomes
found in each cell nucleus of an individual.
Genome: The total genetic material of an
organism, i.e. an organism’s completeset of DNA sequences.
GenomeThe complete set of nuclear and
cytoplasmic genes present in an organism.
Genome-wide association studiesThe markers used
for association studies are distributed, preferably evenly and densely, over
the whole genome.
Genome-wide transcription mapA map depicting
the transcriptional status as well as the expression levels of all the genes
present in the genome.
Genomic estimated breeding value: Of an
individual, the sum total of effects (on trait phenotype) associated with all
the marker alleles included in the GS model applied to the population under
selection.
Genomic imprinting: The phenomenon whereby genes function
differentlydepending on whether they are inherited from the maternal or
paternal parent;this is thought to be caused by information superimposed on DNA
sequences,which is different in male and female gametes; such information is
transmitted, orinherited, in somatic cells but usually erased and reset in the
germ line; it is due tomethylation of one of the alleles depending on its
origin
Genomic in situ hybridisation
(GISH): An in situ hybridisation
technique thatuses total genomic DNA of a given species as a probe and total
genomic DNA ofanother species as a blocking DNA; it is based on fluorescence in
situ hybridisation;it is a useful method to detect interspecific or
intergeneric genome differentiation,chromosome rearrangements (translocations),
and substitutions or additions
Genomic Library. A library
encompassing an entire genome.
Genomic library: A collection of clones made from a set
of randomly generatedoverlapping DNA fragments representing the entire genome
of an organism.
Genomic library: A collection of
plasmid clones or phage lysates containing recombinant DNA molecules that
together, ideally, represent the entire genome of the concerned organism.
Genomic resources: The sum total of
information about the structural and functional aspects of the genome of the
concerned species.
Genomic selection (GS): A method in which the
number of polymorphic bands resembling
the
Genomic selection: A specialized
form of MAS; information from genotype data on all the markers covering the
entire genome form the basis of the selection.
Genomic tiling microarray: A microarray
with a set of overlapping oligonucleotide probes that together represent a part
of the genome of a species at very high resolution.
Genomics. The cloning
and molecular characterization of entire genomes. In other words,it is cloning
and mapping of all the genes present in a genome.
Genomics: The discipline of genetics that
encompasses gene mapping, genesequencing, and determining gene function.
Genomics: The field of study of whole
genomes in terms of their organization and function.
Genomics: The field of study that seeks to
understand thestructure and function of all genes in an organism based
onknowing the organism’s entire DNA sequence, with anextensive reliance on
powerful computer technologies.
Genomics-Assisted Breeding. The
integration and use of genomic tools in breedingpractices for developing
superior lines with enhanced biotic or abiotic stress toleranceand improved
yield. The objective of GAB is to establish and utilize relationshipbetween
genotype and phenotype for crop improvement. GAB includes a range ofapproaches
including genomics, transcriptomics and proteomics to identify themolecular
markers associated with traits of interest to the breeders that help
predictionof phenotype from the genotype to assist breeding.
Genospecies. A genetically
defined species; a group of individuals potentially able tocontribute to or
share in a common gene pool.
Genotype calling: Assigning of SNP
alleles to different individuals in the sample.
Genotype x Environment (GxE): The interaction of a plant’s genotype
with theenvironment in which it is grown that contributes to its performance
Genotype. The genetic
constitution of an organism as distinguished from its appearance(phenotype). It
is the specific allelic composition of an individual or of a cell, whichmay be
of the entire cell or, more commonly, of a certain gene or a set of genes. It
isstable (except for rare changes called mutations) compared to the phenotype,
whichchanges with time.
Genotype: The genetic identity of an individual.
Genotype often is evident byoutward characteristics, but may also be reflected
in more subtle biochemical waysnot visually evident.
Genotype: The specific combination of alleles
present at asingle locus in the genome.
Genotype-Environment Interaction. The change in order, ranking, and relative valuesamong genotypes across
various environments, which are due primarily to macroenvironmentaldifferences.
If genotypes behave consistently, G-E interaction comes tozero, and
consequently genotypes are judged stable. G-E interactions increase rapidlyeven
to unmanageable levels with the increase in the number of
genotypes,environments, and the level of classification. In low-input
agriculture and/ or lowproductivity environments in which most variables are
unpredictable, high G-Einteractions are observed. Consequently, identification
of superior genotypes becomesvery difficult.
Genotypic Frequency. The frequency
at which a genotype occurs in a population.
Genotypic value: Of an
individual/line, the phenotype expected from its genotype.
Genotyping array: In case of DArT,
it contains such genomic DNA segments of a species, which are known to be
polymorphic in a range of germplasm of interest.
Genotyping by sequencing: The genomic DNA
from each individual is digested separately with a frequent cutting restriction
enzyme, the fragments are ligated to a barcoded adapter and a common adapter,
and only the fragments of >1 kb in size and having the common adapter at one
end and the barcoded adapter at the other end are sequenced.
Genotyping: Screening of the individuals of a
mapping population with polymorphic markers.
Genotyping: The process of identifying the genetic
make-up of an organism,by using molecular markers, DNA sequencing, etc.
Genus. A systematic unit that
comprises a group of species having a commonphylogenetic origin and appearing
to be distinctly differentiated from other suchgroups.
Geologic Time. Divisions and
history of life on earth.
Germ Cell. Any of the
reproductive cells in multicellular organisms. It covers bothancestral forms
and their ultimate differentiated products.
Germ cells: Specialised cells that form the
reproductive organ where theyultimately undergo meiosis, thereby producing
gametes that contain half thenumber of chromosomes as there body cells. Germ
cells are responsible fortransmitting genes to the next generation of an
organism.
Germ cells: The sex cell(s) of an organism
(sperm or egg,pollen or ovum). They differ from other cells (somatic) inthat
they contain only half the usual number of chromosomes.Germ cells fuse during
fertilization to begin the nextgeneration.
Germ Line. The cell
lineage from which the gametes are derived in a multi-tissuedeukaryote.
Germinal Mutations. Mutations
occurring in the cells that are destined to develop intogametes.
Germplasm Collection. A collection
of genotypes of a particular species, from differentsources and geographical
locations, used as source materials in plant breeding.
Germplasm enhancement: Any activity that includes gene
transfer via sexualand asexual means from germplasm accessions, or
increasing the frequencies ofdesirable genes in crop gene
Germplasm Theory (Weismann 1834-1914). An accepted theory of evolution thatdisproved pangenesis theory
of inheritance. The theory states that multicellularorganisms give rise to two
types of tissues: somatoplasm and germplasm. Onlygermplasm enters into
reproductive processes and continuity of germplasm betweenall descendant
generations account for the many observed similarities that areinherited.
Somatoplasm, on the other hand, consists of tissues that are essential for
thefunctioning of the organisms but that lack the property of entering into
sexualreproduction.
Germplasm. The sum total
of hereditary materials present in a cultivated speciesincluding related wild
ones. It can also be defined as the genetic material forming thematerial basis
of inherited qualities with capability of being transmitted from onegeneration
to the next by the germ cells.
Germplasm: The genetic material that carries the
inheritance traits of anorganism. Specifically, a collection of diverse genetic
resources that is available tobe used in the development of improved breeding
lines and varieties.
Germplasm: The sum total of all hereditary
material in asingle (interbreeding) species.
GermplasmIn theory, the sum total of the
genetic information, i.e., all the alleles of various genes, present in a crop
species and its wild relatives. In practice, a large collection of different
accessions of the concerned species and its wild relatives.
GISH. Genomic In Situ
Hybridisation; a technique that may
provide a clue to thestructure and evolution of alloploid species and genome
origins. It can also be usedfor monitoring introgression of genes and detection
of chromosomal aberrations, notpossible by other approaches.
Glossary. A partial
dictionary of a particular subject, explaining words, terms, andconcepts.
Glucosinolates. A compound in
the seed meal/cake of rapeseed and mustard that breaksinto toxic sulphur
compounds in the intestines of animals. It has been found to impairgrowth and
reproduction of the animals. Excessive and continuous feeding results
intoenlargement of thyroid glands and ultimately poor growth of ruminants.
Glume. The outer husks or
bracts of each spikelet in grasses.
Glycolysis. Lysis or
splitting of glucose. Under anaerobic conditions, glucose is degradedinto
lactate. If glycolysis is carried out under aerobic conditions, the final
products arepyruvate and coenzyme NADH. Whether aerobic or anaerobic, the
process ofglycolysis is completed in a number of steps with the aid of 10
enzymes, all of which102are located in the cytosol. The net energy yield of
this chain of reactions is theproduction of two molecules of ATP from one
molecule of glucose.
Golden Rice (Ye et al. 2000). Genetically engineered rice capable of synthesizing provitaminA (ß
carotene) in the endosperm thus giving golden yellow colour to the ricegrain.
It contains two genes from daffodil (Narcissus pseudonarcissus) and the
otherone from a bacterium, Erwinia uredovora. The biosynthetic pathway
is:IPPGDP (Geranylgeranyl
diphosphate) Phytoene synthase (daffodil gene1, psy)
Golden rice: A biotechnology-derived rice (Oryza
sativa) created in the 1990sby I. Potr ykus and P. Beyer , which contains
large amounts of beta-carotene,i. e. precursor of vitamin A, in its seeds; the
researchers utilised Agrobacteriumtumefaciens bacteria to genetically
engineer the rice plant, i.e. by inserting thefollowing genes from daffodil and
from the bacterium Erwinia uredovora: (a)phytoene synthase - from
daffodil (narcissus), which converts geranylgeranyldiphosphateinto phytoene;
(b) CRTL gene - from Erwinia uredovora, which codesfor phytoene desaturase,
which causes the rice plant to convert phytoene (a “lightharvesting” carotenoid
involved in photosynthesis) into lycopene (a carotenoidwhich is then utilised
by the rice plant in the production of beta-carotene); and (c)lycopene
beta-cyclase - from daffodil, which converts lycopene into beta-carotene
Goodness of fit: Methods to test the conformity of an
observed empiricaldistribution function of data with a posited theoretical
distribution function (Eg.Chi-square test) by comparing observed
Gossypol. A polyphenolic
compound present in darkly-pigmented glands that occurthroughout the cotton
plant. It reduces the availability of lysine and certain otheressential amino
acids in cottonseed protein, and may cause toxicity if cottonseed mealis fed in
excess to young poultry stocks. The best way to reduce or remove gossypol isto
breed for glandless varieties. The glandless trait is expressed in the presence
of tworecessive genes, gl2 and gl3. These genes do not reduce lint yield or
fibre quality, butinsects have a preference for glandless cotton.
GP4. Genetic resources that
contain specific useful gene(s) from different types oforganisms across texa
that can be transferred through rDNA technology. Such a genepool may be called
a gene ocean.
GR50. The dose of the mutagen
that reduces growth of irradiated materials or individualsto 50%. Like LD50, it
also varies with genotypes (within species) and plant species.Empirical
evidences do suggest that numerical values of these two parameters
(GR50103& LD50) go high for genotypes that are fairly tolerant to abiotic
stresses such as heat,drought, cold, etc.
Grade. A unit of biological
improvement from evolution point of view consisting of agroup of individuals
similar in their level of organization.
Gradient. A gradual change
in some quantitative property over a specific distance.
Graft-Hybrids. Plants in
which tissues of different genotypes exist side by side. In suchhybrids, some
tissues (cell layers) come from the scion and some from the stock.
Grafting. A process of
producing a chimera by vegetative fusion of parts (the scion andstock) from
different individuals.
Gray. The SI unit of
absorbed dose, typically associated with ionising radiation suchas X-rays or
gamma particles or with other nuclear particles. Gray (Gy) is defined asthe
absorption of one joule of such energy by one kilogram of matter (usually
humantissue). Gray, named after the British physicist Louis Harold Gray,
replaces thetraditional unit, the rad (equivalent to 0.01 Gy).
Green fluorescent protein (GFP): Protein from the jellyfish, Aequorea
victoria(Scyphozoa); the gene is used as a reporter gene; it fluoresces in
UV light; severalvariants have been developed, which each exhibit
characteristic spectra; significantadvantages are that the protein
Green Revolution. Sudden and
quantum jump in the production and productivity ofagricultural crops. Dr
William Gadd of the USDA coined the term in 1968. That year,India
experienced its first quantum jump (almost double to that of preceding year,
thatis, about 17.0 million tons) in wheat production, leading to Indian
Governmentreleasing a special stamp titled “wheat revolution”. Significantly,
the stamp had theportrait of the library of IARI, New Delhi to mark the
importance of scientific andknowledge inputs in farming. The Green Revolution
started at first in the Punjab-Haryana regions owing to the presence of several
prerequisites such as ownercultivation, land consolidation and levelling, rural
communication and electrification,existence of a dynamic research and extension
system, assured and remunerativemarketing opportunities, and the like.
Green Revolution: An aggressive effort between 1950
and1975 where agricultural scientists applied modern principlesof genetics and
breeding to improve crops grown primarilyin less developed countries.
Grid design: For the grid design, plants or
variants are divided into blocks andthe best ones chosen from each
Gridding. A technique to
reduce the selection error caused by environmental effects. Itconsists of
dividing the experimental area into small plots (grids) and selecting
equalnumber of superior plants within each grid regardless of the fertility and
moisturegradients. Thus it aids to efficiency of mass selection.
Group II transposonsThese sequences
transpose as DNA molecules.
Growth. The increase in mass
of the organism, which is intimately associated withcellular metabolic
activity.
Growth: An increase in dry mass, volume, length,
or area of a plant as a result of division, expansion, and differentiation of
its cells.
GS model training: Estimation of
the GS model parameters from the phenotype and marker genotype data of the
training population.
Guanine (G): A nitrogenous base, one member of the
base pair G-C (guanineand cytosine).
GUS gene: a gene that codes for production of
beta-glucuronidase (GUSprotein) in Escherichia
Gyanogenesis. The
development of a haploid embryo (individual) from the egg cell.
Gynandromorph. An individual
that is a mosaic of male and female structures. Theunderlying cause is
frequently sex chromosome mosaicism, such that some cells arechromosomal
females, whereas others are chromosomal males.
Gynandromorph: An individual exhibiting both male and
female sexualdifferentiation
Gynodioecy: Plant species or population in which
female plants as well ashermaphroditic plants
Gynoecious. Of plants
having only pistillate flowers.
Gynoecium: The collective term for the female
reproductive organs of a flower,comprising one or more carpel
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