B chromosome: Any chromosome of a heterogeneous
group of chromosomespresent in several plant species, which differ in their
morphology, numericalvariation, meiotic pairing, and mitotic behavior from
normal A chromosomes; theyare also called supernumerary chromosomes, accessory
chromosomes, or extrachromosomes; a B chromosome derives from the A chromosome
complement byaberrant division processes and subsequent modifications
B line: The fertile counterpart or maintainer
line of an A line; does not have fertility restorer genes; used as the pollen
parent to maintain the A line; used inhybrid seed production
B1, B2, …. Symbols used
to designate the first, second, etc. backcross generations. Thesecond and
following backcrosses are made by crossing of individuals of B1, B2,
etc.generations with the same parent.
Bacillus
thuringiensis (Bt): A soil bacterium
that produces toxins that are deadly to some pests. The ability to produce Bt
toxins has been engineered intosome crops.
Back Mutation. A heritable
change in a mutant gene resulting in reversion of the wildtypephenotype or lost
function by so-called forward mutation. A true back mutation,which is a
rare event, restores the original nucleotide sequence of the mutant gene.
Back mutation: A reverse mutation in which a mutant
gene reverts to theoriginal standard form
Backcross Breeding (Harlan and Pope 1922). A system of breeding whereby recurrentbackcrosses are made to one of the
parents of the hybrid, accompanied by selectionfor a desirable character(s).
Backcross breeding A useful trait
is transferred from a donor parent (DP) into a recurrent parent (RP) by
repeated backcrossing to the RP.
Backcross
breeding: A system of
breeding whereby recurrent backcrosses aremade to one of the parents of a
hybrid, accompanied by selection for a specificcharacters
Backcross Cross between
the F1 generation (or a later generation) of a cross and one of its parents.
Backcross inbred lines Homozygous
lines developed by backcrossing the F1 from a cross between two
homozygous lines to one of the parents, followed by continued selfing of the BC1F1
progeny.
Backcross Pedigree. A system of
breeding whereby one or a few backcrosses (2/3/4) aremade to one of the parents
of the hybrid followed by pedigree selection. It providesfor possibility of
obtaining superior transgressive segregants at the cost of losinggenetic
control over breeding population.
Backcross. The crossing
of an F1 hybrid or heterozygote with one of its parents.
Backcross: A cross of an F1 hybrid or
heterozygote with an individual of genotype identical to that on one or the
other of the two parental individuals
Backcross-assisted
selection (BCAS): A method that
allows the selection ofplants carrying a favorable recessive allele at each
generation, limiting the needfor a progeny test, which is common in traditional
backcrossing; in cases wherethe traditional means of selection are limited by
environmental conditions (Eg. thepresence of an abiotic or a biotic stress such
as drought) this selection strategy issuperior to conventional ones;
particularly in genetic transformation approaches, where the transgenes can be
used as markers, BCAS may show a considerableadvantage
Background selection Marker-assisted
selection for the RP genomic regions, except for the target gene/QTL.
Backward
selection: Selection of
parent plants based on results from a progenytest
Bacterial
artificial chromosome (BAC): Pieces of plant DNA that have beencloned inside living bacteria;
they can be used as probes to detect complementaryDNA sequences within large
pieces of DNA via hybridisation techniques, or formarker-assisted
selection by faster selection of segregant-bearing genes for aparticular trait
and to develop future crop varieties faster
Bacteriophage. A virus that
uses bacteria as its host.
Balance. A condition that
refers to adjustment of genetic components in proportions thatgive satisfactory
development. It applies to individuals as well as populations.
Balanced design: An experimental design in which all
treatment combinationshave the same number of observations; there are various
different kinds of balance (variance balance, efficiency balance, etc.), none
of which are equivalent to thecombinatorialist’s pairwise balance, but become
equivalent to it if some extraconditions are satisfied (Eg. in binary
equireplicate uniform block designs)
Balanced
diallelic: The genotype
involving a multiple allelic locus in anautotetraploid where two different
alleles are represented an equal number oftimes (Eg. a1a1a2a2)
Balanced
incomplete block design (BIB): A design in which one constantvalue for the residual variance of
the difference between candidates for all pairs ofcandidates is indicated
Balanced lattice:
A special group
of balanced incomplete block; allowsincomplete blocks to be combined into one
or more separate complete replicates
Balanced lethals:
Recessive lethals
at different loci, so that each homologouschromosome carries at least one
lethal, and associated with inversions, so that norecombination occurs between
the homologous chromosomes
Balanced Polymorphism. Stable genetic
polymorphism maintained by natural selectionunder the condition of selective
superiority of the heterozygote over eitherhomozygotes (overdominance). Suppose
a population that contains three genotypes ata locus, that is, AA, Aa,
and aa. If the fitness of the heterozygote is greater thanhomozygotes,
the population eventually attains equilibrium with a balance proportionof both
homozygotes and heterozygotes. The equilibrium frequency of allele A =
[(WAa – Waa)/(WAa – WAA) + (WAa – Waa)], whereas, W represents the fitness
ofcorresponding genotypes. This frequency also equals to [(Saa)/(SAA + Saa)],
whereas,the letter S represents selection coefficient against the corresponding
homozygotes. Atthe equilibrium, if the population is slightly perturbed, it
will again return to theequlibrium.
Balanced
polymorphism: A genetic
polymorphism that is stable, and ismaintained in a population by natural
selection, because the heterozygotesfor particular alleles have a higher
adaptive fitness than either homozygote; it is referred to as overdominance, as
opposed to underdominance, where theheterozygotes have a lower fitness, giving
rise to unstable equilibrium
Balanced tertiary
trisomic (BTT): A specific
interchange trisomic spontaneouslyselected or experimentally designed in a way
that it is heterozygous (Aaa); itstrisomic progeny after selfing is
genetically similar to the parent; the dominantallele is present on the
translocated chromosome linked to the break point; BTTswere thought to be used
for hybrid seed production in barley; the American variety“Hembar” was the
first commercial hybrid barley
Balanced Tertiary Trisomic (Ramage 1965). A tertiary trisomic set up in such a waythat the dominant allele at a
locus is carried on a translocated extra chromosome andthe counterpart
recessive alleles on the two normal chromosomes. The system usinggenetic male
sterility was proposed during 1960s for producing hybrids in barley.With the
development of CMS system, it has lost its significance.
Balanced
Translocation: Occurs when two
chromosomes break and exchangeplaces leaving the same amount of genetic
material. An individual with a balancedtranslocation will be unaffected, but
children may be affected in a variety of ways.
Balancer. A chromosome
with multiple inversions, used to retain favourable allelecombinations in the
uninverted homologue.
Balancing Selection. Selection
favouring heterozygotes. This kind of selection, for themost part, maintains
more or less balanced polymorphism and thus sustains stableequilibrium in the
populations. It maintains diversity within the population. It mayalso show some
divergence between populations provided environment is differentenough between
them. The opposite process will, of course, produce unstable equilibria. Such
selection will cause homozygosity and divergence betweenpopulations.
Banding pattern: The linear pattern of deeply stained
bands and weaklystaining interbands that results from more or less defined
local differences in thedegree of DNA compactation along the chromosome
Banding: A special staining technique for
chromosomes, which results in alongitudinal differentiation (Eg. Giemsa
staining, which is a complex of stainsspecific for the phosphate groups of DNA)
Barcode identifier sequences Unique short
(4–8 nt long) nucleotide sequences that differ from each other for at least two
bases.
Barr Body. A densely
staining mass that represents an inactivated X-chromosome.
Barriers (to Wide Hybridisation). The sum total of all hindrances encountered whiletransferring genes from
wild relatives to the cultivated species. Pre-fertilizationbarriers include all
factors that hinder effective fertilization. These include failure ofpollen to
germinate, slow pollen tube growth, inability of pollen tube to reach downthe
style, arresting pollen tube in the style, ovary and ovule, and the like. These
can beovercome through manipulation of the chromosome number (of the parent
species),bridge cross technique, shortening style, use of recognition mentor
pollen, growthhormones, in vitro/vivo fertilization, protoplast
fusion, etc. Post-fertilization barriershinder or retard development of the
zygote and normal development of seed including25reproductive abnormalities in
hybrids (hybrid inviability and sterility) and latergenerationprogenies
(hybrid break-down).
Base Analogue. A chemical
whose molecular structure mimics that of a DNA base.Owing to mimicry, the
analogue may act as a mutagen through mispairing.
Base analogues: A purine or pyrimidine base that
differs slightly in structurefrom a normal base, but that because of its
similarity to that base may act as amutagen when incorporated into DNA (eg.,
uracil, 5-bromouracil, 5-fluorouracil,5-methylcytosin, 5-bromocytosin,
hypoxanthin)
Base calling: IN DNA/RNA sequencing, deduction of bases on
the basis of light color and intensity signals.
Base collection: A collection of germplasm that is kept
for long-term, secure conservation and is not to be used as a routine
distribution source; seeds are usually stored at sub zero temperatures and low
moisture content.
Base Collections. Accessions
that serve as a broad germplasm base for possible futureuse by plant breeders.
The base collections are maintained for long periods. This callsfor taking
special pains so as to avoid any genetic change likely to be brought inthrough
mutation and other mechanisms.
Base pair (bp): Two nitrogenous bases (adenine and
thymine or guanine andcytosine) held together by weak bonds. Two strands of DNA
are held together inthe shape of a double helix by the bonds between base
pairs.
Base population: The initial set of genotypes from
which selections will betaken to establish a breeding population, for example,
the wild forest; it is alsosometimes referred to in the same meaning as
recruitment population (in thefirst generation they are actually the same, and
it can be referred to as one of thepopulations in a stratified tiered
structure)
Base sequence
analysis: A method,
sometimes automated, for determining thebase sequence based on some sets of postulates
Basic Number. The number of
chromosomes in any one genome. It is also called themonoploid number. It is
usually designated by x. Allard (1960) has defined it as thenumber of
chromosomes in ancestral diploid ancestor of a polyploid.
Basic number: The haploid number of chromosomes in
diploid ancestors ofBatch culture: A cell suspension grown in liquid
medium of a set volume; inocula of successive subcultures are of similar size
and cultures contain about thesame cell mass at the end of each passage;
cultures commonly exhibit five distinctphases per passage (a lag phase follows
inoculation, then an exponential growthphase, a linear growth phase, a
deceleration phase, and finally a stationary phase)
Basmati Rice. Also called aromatic or scented rice. It emits typical aroma or
scent (bas=aroma) in fields, at harvest, in storage, during milling, cooking
and eating. It hasspecial grain quality, for example, intermediate amylose
content (21-25%), mediumgelatinization temperature (65-70°C), soft gel consistency,
high grain elongation oncooking, and a typical aroma (as in Basmati 370). The
aroma is due to a volatilecompound, known as 2-acetyl-1-pyrroline.
They are tall indica types with poor yield.Attempts have been made to
improve it, and now semi-dwarf types are available..
Bayes factor: The ratio of
the probability of getting the observed data when H1 is correct to that when Ho
is true.
BC1, BC2,… . Symbols used
to designate the first, second, etc. backcross generations.
B-chromosomes. Small plant
chromosomes of variable number between individuals of aspecies with no known direct
phenotypic role. These are also called supernumerary orextra chromosomes.
Randolf (1928,’46) reported their presence in maize and Longleynamed them B-chromosomes.
These are largely heterochromatic, and there is fairlyhigh distribution of
B-chromosomes in maize. Certain strains of Indian corn do notbear these
chromosomes, while in others they may go up to 25 or even more.
Bead Theory. The disproved
hypothesis that genes are arranged on the chromosome likebeads on a necklace,
indivisible into smaller units of mutation and recombination.
Beavis effect: The smaller is
the size of a mapping population, the smaller is the number of detected QTLs
for a trait and the larger are the estimates of their effects.
Bias. A consistent and false
departure of a statistic from its proper value.
Bimodal Curve. A curve with
two-mode distribution of a variable.
Bimodal Distribution. A statistical
distribution having two modes.
Bin mapping: In this approach,
the linkage map is divided into several relatively small segments called bins,
and the markers are mapped within individual bins.
Bin: In case of
linkage maps, a relatively small (typically 10–20 cM long) segment of a linkage
group that is flanked by fixed core, anchor, or framework marker loci. In case
of selective mapping, an interval in a linkage group within which a breakpoint
has not occurred in any individual included in the sample. In case of MAPMAN
tool, a specific area of metabolism, e.g., photosynthesis.
Binary image: A segmented
image.
Binary vector
system: A two-plasmid
system in Agrobacterium tumefaciens fortransferring into plant cells a
segment of T-DNA that carries cloned genes; oneplasmid contains the virulence
gene (responsible for transfer of the T-DNA), andanother plasmid contains the
T-DNA borders, the selectable marker, and the DNAto be transferred
Biochemical Genetics. A branch of
genetics dealing with the chemical nature of genesand their mode of action in
development and function.
Biochemical Markers. Biochemicals
such as proteins or enzymes used to identify aparticular biological structure
or function. They are limited in number, and specific totissues and
developmental-stages. However, they can be used reliably in the selectionof superior
genotypes. These are inexpensive, and can be generated on a large scale.
Biodiversity: The existence of a wide variety of
species (species diversity),other taxa of plants or other organisms in a
natural environment or habitat, orcommunities within a particular environment
(ecological diversity), or of geneticvariation within a species (genetic
diversity
Biofertilizers. A misnomer
that includes a variety of biological agents such as blue greenalgae, azolla,
rhizobium, azospirillum, and a host of green manure and green leafmanure crops
including the stem nodulating Sesbania rostrata.
Biofortification. Genetic
modification and bioprocessing for the improvement ofnutritional quality of
food. It is beneficial in developing countries compared to thedeveloped ones,
which have easy access to alternative means for meetingrequirements of mineral
nutrients and vitamins. Recent developments of golden rice,high iron rice, high
protein potatoes are but a few examples of genetic fortification.
Biofortification:
The process of
breeding food crops that are rich in bioavailablemicronutrients; these crops
fortify themselves that is, they load high levels ofminerals and vitamins in
their seeds and roots, which are then harvested and eatenby animals or humans;
through biofortification, breeders can provide farmerswith crop varieties that
naturally reduce anemia, cognitive impairment, and othernutritionally related
health problems, potentially for use in third-world countries
Bioinformatics tools: Computer
programs for acquisition and analysis of data, for detection of associations
and patterns, or for achieving other specific objectives.
Bioinformatics. A truly
inter-disciplinary subject that combines biology, mathematicsand computer
softwares. It involves the use of information technology in studyinglife
sciences: a combination of IT and biotechnology. All the information (results)
ofmolecular biology are based on experiments on the theory of trial and error.
Also, itrequires costly chemicals, time and wastage of labour. This wastage can
be avoidedwith bioinformatics because simulation of protein sequences using
mathematicalmodels in computers and studying them helps us save a lot of time,
and providesquicker and accurate results.
Bioinformatics. Use of computer programs for searching
and analysing electronic databases of DNA and protein sequences. This branch of
science is animportant component of molecular biology and genetics.
Bioinformatics: A broad term to describe
applications ofcomputer technology and information science to organize,
interpret, and predict biological structure and function. Bioinformatics is
usually applied in the context of analyzingDNA sequence data.
BioinformaticsDerived from the
terms “biology,” “information technology,” and “statistics”; it involves
development of statistical tools and techniques and computer software for
acquisition, storage, analysis, and visualization of biological information.
Biolistics. The process of introducing DNA into
plant cells by shooting DNAcoatedpellets into the cell using a compressed air
delivery system know as a genegun.
Biological Nitrogen Fixation. The fixation of atmospheric nitrogen in form of proteinby microorganisms
such as bacteria. Such bacteria contain nif genes, expression ofwhich
lead to the production of an enzyme, called nitrogenase. This enzyme
convertsfree nitrogen into ammonia, then to amino acid and ultimately to
protein.
Biological Yield. The total
yield of a plant material.
Biometrical Genetics. The
statistical description of similarity and differences betweengroups of
organisms for the characters showing continuous variation. It usesstatistical
parameters such as means, variances, covariances, and the like. It is thefusion
of two approaches, that is, genetical and biometrical to the understanding
ofcontinuous variation. The former gives us principles on which the analysis
must bebased; the latter shows the way in which to handle continuous variation.
Biometrical
genetics:
A branch of genetics which utilizes statistical concepts and procedures for the
study of genetical principles.
Biometry. Also called biometrics.
The branch of science that deals with statisticalanalysis of biological
observations.
Biometry: The science
which deals with application of statistical concepts and procedures to study
biological problems also called as Biometry.
Biopesticide. A pesticide of
biological origin. Among biopesticides, BT protein, which isproduced by a soil
borne bacterium, Bacillus thuringiensis, is the most important. InIndia,
its use was banned till 1991 because of the fear that spores of BT will
affectsilkworm. To circumvent this problem, non-sporulating strains of BT,
which are toxicto specific insects, have been developed at NRC for Plant
Biotechnology.Biopecticides have received special attention as: (a) these are
environment friendly,(b) these are not carcinogenic, and (c) they operate with
a high degree of insectspecificity.
Biophages. Organisms that
consume other living things.
Biopharming: The production of pharmaceuticals suchas edible vaccines and
antibodies in plants or domestic animals.
Biopharming: The use of genetically transformed
crop plantsand livestock animals to produce valuable compounds,
especiallypharmaceuticals. Also called pharming.
Bioremediation: The use of biological organisms to
renderhazardous wastes non-hazardous or less hazardous.
Biotechnology. A technology
involving living organisms and molecules as means ofproduction while using a
variety of techniques such as tissue culture, cloning, cellfusion, embryo
transfer, rDNA technology, and the like. It is seen as the mostpowerful
technology having the potential to pave the way for evergreen revolution.
Biotechnology: A set of biological techniques
developed through basic researchand now applied to research and product
development. In particular, the use by industry of recombinant DNA, cell fusion
and new bioprocessing techniques.
Biotic stressInfection by a
virus, fungus, nematode, or bacterium or infestation by an insect.
Biotype. A group of individuals
having same genetic constitution. The group may behomozygous or heterozygous.
The term is used more frequently by entomologists, andis analogous to the
physiological race of a pathogen. Biotypes of insect pests are lessfrequent
compared to physiological races of pathogens because: (a) insects’physiology
are complex, (b) pest resistance in host plants is often related to the
hostfindingbehaviour of insects, (c) most of the insects have more than one
hosts(polyphagous), and (d) asexual mode of reproduction is not so
well-developed as inpathogenic fungi. The frequency with which new biotypes of
insect pests is producedis directly related to the selection pressure exerted
by the resistant cultivar and modeof reproduction of insect pests. All the
above four phenomena tend to reduce selectionpressure by the insects
themselves. The techniques used to characterize differentpathotypes are also
applicable to distinguish different biotypes.
Biparental
inheritance: Plant zygotes
that show traits indicating chloroplastchromosomes from
Biparental Mating Design. A mating
design that is based on the evaluation of biparentalprogenies. Male and female
of a particular biparental mating is never used for thesecond biparental
mating. Thus (½)n progeny family is produced. In this design,genetic variance
is overestimated relative to environmental component of variation. Itis the
simplest method, and can be utilized in both self- and cross-pollinated crops.
Inaddition, a large number of BIPs can be included and compared. The
maindisadvantage of the method relates to its incapacity to provide for
detection ofepistasis.
Biparental Mating. A form of
mating between randomly selected two individualsusually in segregating
generations (such as F2, F3, etc). In such generations, eachindividual is
different from the other, and may be heterozygous for different genepairs;
thus, mating between them is expected to break undesirable linkage andprovides
favourable gene combinations. In clonally propagated crops (such as potatoand
sugar cane), F1 itself is a segregating generation as each parental individual
ishighly heterozygous. Thus, crossing between any two individuals either in
parentalgeneration or in F1 generation corresponds to biparental mating.
Biparental
populations: The progeny
derived after crossing two genotypesas male and female parents; such
populations include F2 genotypes generatedfrom F1 progeny, lines
generated after doubling the haploids (DHs, obtained fromF1 plants through
anther, egg cell or ovule culture or distant hybridisation), orrecombinant
inbred lines (RILs), which are derived by single seed descent for atleast five
or more generations by repeated selfing or sibling mating
Bisexual. Of organisms
having both male and female reproductive organs producingrespective gametes; of
flowers having both stamens and pistils inside them.
Bisexual: Species comprises individuals of both
sexes or a hermaphrotideorganism in which an individual plant possesses both
stamens and pistils in theflower
Bivalent
formation: The association
of two homologous chromosomes as aring or rod configuration depending on
chiasma formation
Bivalent. A pairing
configuration during the first meiotic division that consists of twocompletely
or partially homologous chromosomes. The number of bivalent permeiocyte equals
half of the somatic chromosome number of diploid species.
Bivalent: Two homologous chromosomes when they
are paired duringprophase-metaphase of the first meiotic division
Bivariate
statistics: Statistics that
describe the relationship between twovariables
BLAST (Basic Local Alignment
Search Tool): A
family of user-friendly sequence similarity search tools for identification of
database sequences homologous to the query or submitted nucleotide or protein
sequence. The most popular data-mining tool developed ever.
BLASTn: It compares
the query nucleotide sequence with a nucleotide sequence database.
BLASTp: It compares
the submitted protein sequence against a protein database.
BLASTx: It translates
the submitted nucleotide sequence into an amino acid sequence and compares the
latter with a protein database.
Blended variety: Multiline variety
Blending Inheritance. A discredited
model of inheritance suggesting that thecharacteristics of an individual
results from mixing of the essences(pangenes/gemmules) from its parents.
B-Line. The fertile
counterpart of A-line. It is also called maintainer of A-line. It has‘fertile’
cytoplasm; however, it does not have fertility restorer nuclear gene(s).
Thefertile cytoplasm enables it to produce fertile pollen and thus it is used
to maintain Aline.
Blocking. The process of
putting together experimental units as similar as possible in thesame group (referred
to as block). The number of block is equal to the number ofreplication. Thus,
all the treatments are included into each block separately andindependently.
Blocking facilitates measurement of variation among blocks and itsremoval
from experimental error.
Blotting: Transfer of
molecules from a gel onto a solid support. In Southern hybridization, transfer
of DNA fragments from the gel onto a solid support like a nitrocellulose filter
membrane.
Blunt ends: DNA fragments that are double-stranded
paired over the wholelength, usually produced by certain types of restriction
enzymes
Blunt-end
ligation: Ligation of DNA
with blunt ends requires higherconcentration of DNA ligase than sticky-end
ligation; it is inhibited by ATPconcentrations
BOAA. β-oxalyl amino α-alanine.
It has also been designated ODAP (β-oxalyl diaminopropionic acid). The
neurotoxin is found in the seeds of grass pea. Its continuedconsumption is
associated with a disease, called lathyrism (paralysis of lower limb).There are
certain cultivars (e.g., Ratan, Prateek, etc), which have negligible
BOAA(ODAP) content.
Boll. The fruiting body of
cotton. It consists of lint and seeds besides outer coverings.
Bollgard
insect-protected cotton: A genetically improved cotton that offersprotection against the
cotton bollworm; the bollworm can cause significant damageto a cotton crop and
require repeated applications of insecticides; Bollgard. cottoncontains an
insecticidal protein from a naturally occurring soil microorganism, Bacillus
thuringiensis, that gives cotton protection from bollworms both parents are
present and active
Bolting. Production of seed
stocks the first season in a biennial crop, as in sugar beet.
Bottleneck: A marked
reduction in the size of a population for one or more generations.
Bottleneck: A period when a population becomes
reduced to only a few individuals; a form of genetic drift that occurs when a
population is drasticallyreduced in size; some genes may be lost from the gene
pool as a result of chance
Breakage-reunion
hypothesis: The classical and
generally accepted model ofcrossing-over by physical breakage and crossways
reunion of broken chromatidsduring meiosis.
Breakdown of resistance:
The inability of
a plant to maintain resistance whenattacked by a pest biotype that has a gene
for virulence at every locus corresponding to a gene for resistance in the host
Breeder Seed. The seed or
vegetative propagating material produced by or under directcontrol of the plant
breeder or agency sponsoring a variety. It is used to producefoundation seed.
Breeder’s
collection: Working
collection
Breeder’s exemptionThe protected
variety can be freely used for scientific purposes and for creation of genetic
variability in plant breeding programs.
Breeder’s rights:
Varietal
protection; the legal rights of a breeder, owner, ordeveloper in controlling
seed production and marketing of crop varieties
Breeder’s seed: Seed or vegetative propagating material
increased by theoriginating or sponsoring plant breeder or institution; it
represents the truepedigree of the variety; it is used for the production of
genetically pure, foundation, registered, and certified seeds
Breeders’ Right. Breeders’/researchers’
interests. It implies exclusive authority of plantbreeders over what comes out
of their experimentation (plant variety, for example).And, protection for plant
breeders’ rights is called varietal protection. If plantbreeders’ rights are
safeguarded, farmers’ interests will ultimately be marred.However, the
Government of India is trying to protect the rights of both.
Breeding cycle: The shortest period between successive
generations fromgermination of a seed to reproduction of the progeny (i.e. the
seed-to-seed cycle)
Breeding line: A group of plants with similar traits
that have been selected for their special combination of traits from hybrid or
other populations; may bereleased or used for further breeding approaches. A
genetic group that has been selected and bred for its special combinations of
traits.
Breeding Nursery. A place for
rearing of breeding materials under a specific condition.
Breeding
population: A group of
individuals selected from a wild, experimental or crossing population for use
in a breeding program; usually phenotypicallyselected for desirable traits. In case of
genomic selection, the population subjected to GS.
Breeding Size. The number of
individuals in a population that are actually involved inreproduction in a
given generation.
Breeding System. A system
comprising all variables excluding mutation that affect thegenetic relationship
of uniting gametes in sexual reproduction. These variables areclassified into
two groups: (a) those, which affect the ability of particular parents tomate or
gametes to fuse, and (b) those, which affect the probability of mating
ofparents or of fusing of gametes. The first group of variables constitute the matingsystem.
The breeding system controls the extent of outbreeding through variousforms: exclusive
outbreeding, predominant selfing, and a mixture of selfing andcrossing.
Breeding system: The system by which a species
reproduces; more specifically the organisation of mating that determines the
degree of similarity and/ordifference between gametes effective in
fertilisation
Breeding Value. Performance of
a parent adjudged by the mean performance of itsprogenies following some
definite systems of mating. It is a more authentic index ofan individual’s true
genetic potential than its per se performance. It equals the sum ofthe
average effects of the genes contained in its genotype. The b.v. is closely
related toparent-offspring correlation and is nothing but general combining
ability effect ofeach parent in cross combinations. Since segregating generations
are not identical tosingle crosses (F1’s), b.v. is obtained from hybrid
progenies only. However, itamounts to half the deviations of its progeny mean
from the population mean whenthe genotype mates at random with other members of
the population.
Breeding value: The mean genotypic value or the
progeny of an individual expressed as a deviation from the population mean. Of an
individual/line, the expected phenotypic value of its progeny. The value of an individual as defined
by the mean value of its progeny, either on the basis of individual traits or a
selection index
Breeding. The controlled
evolution of plants and animals by humans with the goal ofproducing populations
that have superior agricultural and economic characteristics.
Breeding: The intentional development of new
forms or varieties of plants or animals by crossing, hybridisation, and
selection of offspring for desirablecharacteristics. The science and art of
manipulating the heredity ofan organism for a specific purpose.
Bridge cross: A method of bypassing an
incompatibility barrier betweentwo genotypes or species by using a third
genotype or species, which is partlycompatible with each of them, in an
intermediate cross
Bridge-breakage-fusion-bridge
cycle: A process that
can arise from theformation of dicentric chromosomes; daughter cells are formed
that differin their content of genetic material due to duplications and/or
deletions in thechromosomes
Bridging Cross (Sears 1956). A cross made to transfer alleles between two sexuallyisolated species by
first transferring them to an intermediate species that is sexuallycompatible
with both. It is also called Sears’ technique. He wanted to transferresistance
to leaf rust from Aegilops umbellulata (CC) to common wheat (AABBDD),but
found it difficult due to crossability barrier between these two species. He
firstmade a cross between A. umbellulata and T. dicoccoides (AABB).
The chromosome ofthe F1 was doubled. Thereafter, the doubled hybrid was crossed
to T. aestivum and theresulting F1 was backcrossed twice to T. aestivum.
He got a leaf-rust resistant plantthat carried an extra chromosome. Then
irradiated pollen from this plant was used topollinate T. aestivum.
He got a plant with leaf rust resistance as well as normalchromosome
complement. Apparently, the gene(s) for resistance was translocated toone of
the chromosomes (near kinetochore) of T. aestivum through a
process calledunidirectional insertional translocation. When bred to
homozygosity, the resistantplants were indistinguishable form parental ones
except for slightly later maturity. Inthe entire crossing programme, T. dicoccoides
acted as the bridge species.
Bridging-Host Hypothesis (Ward 1902). A discouraging hypothesis towards breedingfor disease resistance. It
assumed that breeding for resistance is futile because thepathogen can produce
new races in steps with the breeding of new varieties, and thusresistance would
decline in the new varieties as fast as they are produced. Thehypothesis made
two-fold impacts: (1) it discouraged many from attempting to breedfor
resistance, and (2) it necessitated further investigations to search for
themechanisms by which new pathogenic types would appear from the previous
ones.
Broad Genetic Base. Having high
genetic variability as in an open-pollinated variety.
Broad-sense
heritability: The ratio of
total genetic variance to phenotypicvariance; it is used to estimate the degree
of genetic control of a trait in a population and it is useful for predicting
response to clonal selection
Bt (Bacillus
thuringiensis): A naturally
occurring bacteriumthat produces a protein toxic to certain lepidopteran
insects.
Bt Crops. Genetically
engineered crops known to carry stably integrated and expressedBt genes (Cry
genes). Maize, rice, cotton and several other crops have beengenetically
modified with Bt genes. These genes lead them to produce delta
endotoxinprotein, which upon hydrolysis in alkaline environment of the mid-gut
releases deltaendotoxins. These toxins through several intermediate reactions
cause paralysis of thedigestive systems and lead to the death of the insect. A
cotton variety, Boll Guard,which is a product from a multinational company, is
known to carry such a gene (Cry1Ac). Apprehensions have been raised that
the widespread cultivation of such cropsmay cause intense selection pressure on
the insects, and Bt genes are likely to be fixedin the insect populations. Upon
fixation, such crops will become ineffective as insectcontrolagents. The second
apprehension relates to exposure of human populationscontinuously to such
Bt-proteins.
Bt crops: Crops that are genetically engineered
to carry a gene from the soilbacterium Bacillus thuringiensis (Bt). The
bacterium produces proteins that aretoxic to some pests but non-toxic to humans
and other mammals. Crops containingthe Bt gene are able to produce this toxin,
thereby providing protection for theplant. Bt corn and Bt cotton are examples
of commercially available Bt crops.
Bt Genes. Genes (from
the Gram Positive soil bacterium Bacillus thuringiensis)encoding
insecticidal crystal proteins (ICPs). ICPs are commonly designated “Cry”proteins,
and the genes encoding them are better known as “Cry” genes. Over
fiftysuch genes (Cry1Ac, Cry1C, Cry1B, Cry1D, and the like) have been
identified andsequenced. These are effective against caterpillars of Lepidopteran
insects. The genehas been incorporated in several crops including cotton.
The gene product is acrystalline protein, which remain in such plants in active
form. When the insectutilises such plants as its food, the crystalline protein
causes paralysis of mid-gut, andthe insect ultimately dies.
Bud Pollination. Placement of
mature pollen on immature stigmas. This may allowslow-growing incompatible
pollen tube to reach ovary in time so that fertilization mayoccur. The
rationale is that stigma accumulates inhibitory biochemical substancesonly if
it gets matured. As temperature also plays an imortant role in the
accumulationof such inhibitory biochemicals, pollinating at low temerature may
also accomplishthe same purpose.
Bud pollination: A procedure utilised in maintaining
self-incompatibleparent lines by self-pollination; hybrid seed production in
plant species havinga sporophytic self-incompatibility system is dependent upon
the production ofinbred lines homozygous for a self-incompatibility allele S
Bud Sport. A somatic
mutation expressed in a bud or branch of plants. Also called budmutation.
Bulbosum Technique (Kasha and Kao 1970). A technique to induce haploids bycrossing a species with Hordeum
bulbosum. Haploids of cultivated barley have beenproduced through this
technique. When diploid cultivated barley (H. vulgare) iscrossed with a
diploid wild relative (H. bulbosum), fertilization occurs; but during
theensuing somatic cell divisions, the chromosomes of the wild relative (H.
bulbosum)are preferentially eliminated from the zygote resulting in a
haploid embryo. (Thehaploidization process seems to be caused by a genetic
incompatibility betweenchromosomes of different species). Although originally
proposed for barley,pollination of bread wheat with H. bulbosum also
results in haploid plantletproduction.
Bulk breeding: The growing of genetically diverse
populations of self pollinated crops in a bulk
Bulk generation: In the breeding process, one or more
generations in whichplants of a genetically diverse population of autogamous
crops are grown in abulk plot with or without mass selection
Bulk Population Breeding. The growing of
genetically diverse population ofautogamous crops in a bulk plot for several
generations with or without massselection followed by individual plant
selection. During the period of bulking, naturalselection usually determines
the course of differentiation, and hence it is also calledevolutionary method
of plant breeding.
Bulk population
selection: Selection
procedure in self-pollinating crops; segregating populations are propagated as
bulks until segregation has virtuallyceased, at which time selection is
initiated
Bulked segregant
analysis (BSA): A
rapid mapping strategy suitable formonogenic qualitative traits; when DNA of a
certain number of plants is bulkedinto one pool, all alleles must be present;
two bulked pools of segregants, differingfor one trait, will differ only at the
locus harboring that trait
Bulked segregant analysis: Equal amounts
of DNA from 10 plants from each of the two most extreme phenotypic groups for
the target trait are bulked to create two bulks; DNAs from the two parents and
the two bulk DNAs are screened with a large number of markers to detect markers
putatively linked to the genes governing the target trait.
Bulked segregant RNA-Seq: A modification
of BSA; it uses RNA sequence data from the two phenotypic extreme bulks to
identify markers tightly linked to the gene responsible for the target trait.
%20(2).png)
0 Comments