A Chromosome. Any member of the normal chromosome complement in
contrast to the B-chromosomes.
A Line. The
male-sterile parent line to produce hybrid seed. It is the seed-producing line,
always used as the female parent. It has ‘sterile’ cytoplasm and recessive
nuclear gene(s).
A line: The seed-bearing parent line used to
produce hybrid seed that is male sterile
A matrix: matrix contains the proportion of alleles that
are identical by descent for each pair of individuals in a sample.
A Posteriori. Derived by reasoning from observed facts (data).
A Priori. Based on hypothesis or theory rather than on
experiments or experience.
Ab initio gene prediction Gene prediction
by using specialized software for searching genome sequences for the presence
of genes.
Aberration: Variation of chromosome structure
caused by induced or spontaneous mutations; in
Abiotic stress an abiotic
environmental factor that produces an adverse effect on crop performance.
Abiotic Stress. Any kind of abnormal condition due to non-living
components of environment (high or low temperature and moisture, high salinity
or acidity in soil, for example) that adversely affects growth and reproduction
of crop plants. Breeding for abiotic stress is considered more difficult
because of: (a) complexity of conditions causing abiotic stresses, (b) complex
nature of abiotic resistance in a variety, (c) occurrence of one stress more
often in conjunction with the other, (d) low heritability of abiotic
resistance, and (e) variable intensity of such stress under field condition.
AB–QTL Method (Tanksley and Nelson 1996). (Advanced Backcross QTL Method)It is a method for simultaneous discovery and
transfer of valuable QTLs from unadapted germplasm into elite breeding lines.
It involves use of BC2/BC3 (or their self or testcross
progenies) for phenotyping and genotyping using molecular markers. Such
populations are non-random resulting from intense selection in BC1/BC2 and
allow to identify yield and yield component QTLs. Using this method, two wild QTL
alleles namely, Yld 1.1 and Yld 2.1 from O. rufipogon (using
‘RM5’ and ‘RG256’ markers, respectively) have been identified and introgressed
into cultivated hybrid rice. Each of the two has been shown to confer yield
advantage of more than 18% in the hybrid rice. It has been also used to
identify such genes in Lycopersicon prempenellifolium. One of the main
demerits of this method is that BC2/BC3 populations are effective for detecting
dominant and overdominant QTLs only; recessive QTLs go undetected.
Acaryotic. Referring to a cell without nucleus.
Acceptable cluster A group of two
or more entities, for which within cluster GD is less than the overall mean GD.
Accession: A distinct, uniquely identified
sample of seeds, plants, or other germplasm materials that is maintained as an
integral part of a germplasm collection.
Accessory
chromosome: A chromosome that
is present in addition to the normal chromosome complement i.e. B chromosome
Accessory Chromosomes. Sex chromosomes and other supernumerary chromosomes
such as B chromosomes.
Acclimatization. The ability of a population to recover and adapt to a
new climatic situation. The process of acclimatization is a population
phenomenon. Unfit genotypes of the population are eliminated and the frequency
of the ‘fit’ increases generation after generation. After a few generations,
the performance of a population is better once all the unadapted types get
eliminated. Thus, it is the result of genetic shift towards the adapted types.
The efficiency with which it takes place depends on: (a) genetic variance of
the population, (b) mode of reproduction and (in sexually reproducing plants)
pollination, and (c) the nature and intensity of environmental stresses. One
should note that it is not a breeding method; instead, it explains the process
by which new introductions gradually become adjusted and established as a
better performing population.
Acclimatization: Adaptation of an introduced variety to
the new environment
Accuracy of mapping the closeness
of the QTL position and effect size estimates obtained from a study to their
“true” values.
Acentric Chromosome. A chromosome without the centromere.
Acentric: Chromosome, chromosome segments, or
chromatids that show no centromere
Acetolactate
synthase (ALS): An enzyme essential
for amino acid production
Acrocentric Chromosome. A chromosome having the centromere located slightly
nearer to one end than the other.
Active Collections. Genetic resources maintained for immediate use by the
plant breeders. Such collections are for multiplication, regeneration,
evaluation, documentation, distribution, and use by breeders. These collections
have frequent usage and obviously need frequent multiplication. The storage
period is, therefore, short (1-2 years) or at best medium (3-4 years).
Active Resistance. A type of resistance reaction of the host plants
induced in response to the attack by a parasite. The formation of phytoalexins
(antifungal compounds) in some host plants in response to inoculation with
certain pathogens is an example of such resistance. It is known that seedlings
of cotton are susceptible to many a pest owing to the absence of gossypol;
but once infected by Verticillium, plants begin to synthesize gossypol
and seedlings become resistant. Normally, only mature plants have gossypol and
not the seedlings.
Active Site. The part of a protein that must be maintained in a
specific shape if the protein is to be functional; for example, in an enzyme,
the part to which the substrate binds.
Active Variability. Also called free variability; genetic variability that
is freely expressed as phenotypic differences between homozygotes and thus is
exposed to selection. This is immediate cause of response to selection, for
example, difference between AA and aa.
Ad hoc index A selection
index based on marker genotype and trait phenotype data from the same
population in which it will be used.
Adapatedness: The degree or capacity of an
individual to survive in a local environment and to transmit its genotype to
the next generation.
Adaptability. The ability of a genotype to adapt under given
environmental conditions; the potentiality for adaptation; flexibility or
capacity to change in adaptedness (fitness).
Adaptation. The process by which individuals (or parts of individuals),
populations or species change in form or function in such a way to better
survive under given environmental conditions. Also the result of the process.
Adaptedness. The degree of suitability (fitness) of an organism for
its environment, developed over time as a result of selection. Alleles which
are predominant in most of the cultivars and breeding stocks representing a
broad range of environments make significant contributions towards wide
adaptedness and high productivity in nearly all genetic backgrounds and in
nearly all environments. Alleles with intermediate-to-high frequencies in the
varieties and breeding stocks of some (but not all) eco-geographical regions,
on the other hand, make differing contributions to adaptedness and performance
in different eco-geographical regions and in different genetic backgrounds with
year-to-year variations. This class of alleles may enter into favourable
inter-locus interactions (epistasis) in diploids as well as polyploids.
Favourable epistasis (acting to assemble and sustain favourable multi-locus
genotypes) is indeed a major mechanism responsible for adaptedness (biological
fitness) in natural populations.
Addition line: A cell line or line of individuals
carrying chromosomes or chromosome arms in addition the normal standard
chromosome set
Additive Effect. The plus effect produced by the presence of each
additional gene on the phenotype. Either of the two genes may produce the same
effect, but the effects are additive if both genes are present. For example, in
barley, A or B produce medium awns, while together produce long awns and thus
giving an F2 ratio of 9A-B-(long awns): 6aaB-/A-bb (medium awns): 1aabb
(awnless).
Additive Gene Action. The way the linear quantitative effect (plus or minus)
associated with the substitution of one allele for the other at a given locus
is produced on the phenotype. This change occurs on the phenotypic scale of
measurement regardless of presence of genes at other loci. For example, 1. 1AABB
(7), 2AaBB (5), 1aaBB (3) → replacement of a by A leads to a change
of 2 units, 2. 1AABB (7), 2AABb (6), 1aabb (5) → replacement of b by B leads to a change
of 1 unit. The replacement effect is the same whether it occurs in a homozygote
or heterozygoteand is also constant regardless of the phase at other locus. It
is interesting to note that the mean values in these examples are 5 and 6,
respectively. So replacement of a for A is by two units and of b
for B by one unit; this is called the average effect of an
allele. Thus it can also be defined as the type of gene action in which the
change is associated with the average effect of substituting one allele for the
other at a given locus.
Additive gene
effect: The effect of
an allele expected after it has replaced another allele at a locus.
Additive genes: Gene interaction without dominance (if
allele), or without epistasis (if nonallele).
Additive Genetic Variance. That portion of genetic variance which describes
difference between homozygotes at any given locus. In the examples quoted under
additive gene action, the numerical values of additive variance
amounted to 2.0 and 0.5 unit2, respectively which were produced as a
consequence of additive effects of 2.0 and 1.0 units, respectively. Thus, one
can also define it as that portion of genetic variance which is produced by
additive gene action. As additive gene action itself is dependent upon the
average effect of substitution of one allele for the other, thus it can be
appropriately defined as that portion of the genetic variance which is
associated with the average effect of substituting one allele for another at
one, two, or more loci.
Additive
resistance: Resistance
governed by more than one gene, each of which can be expressed independently,
but which is reinforced by the expression of each of the additional genes
Additive variance
(VA): The proportion of
the genetic variance due to additive effects
Address sequence IN SNP
genotyping, the tag oligo for a given bead type.
Adenine. One of
the two purine bases that normally pairs with thymine in the DNA double helix.
Adenine: A nitrogenous base, one member of the
base pair A-T (adeninethymine).
Adenosine
diphosphate (ADP): High-energy
phosphoric ester (nucleotide) of the nucleoside adenosine that functions as the
principal energy-carrying compound in the living cell
Adenosine
triphosphate (ATP): High-energy
phosphoric ester (nucleotide) of the nucleoside adenosine that functions as the
principal energy-carrying compound in the living cell
Adenosine. The nucleoside containing adenine as its base.
Adjacent
segregation: A reciprocal
translocation heterozygote in which duringmeiosis the segregation of a
translocated and a normal chromosome happens together, giving unbalanced
gametes with duplications and deficiencies leadingto nonviable zygotes; adjacent
segregation is of two kinds depending on whether nonhomologous (adjacent-1) or
homologous (adjacent-2) centromeres segregate together; adjacent-1 segregation
is the usual type of adjacent segregation and adjacent-2 segregation is rare
Adjacent-1 Segregation. A kind of segregation in a translocation heterozygote
in which each of the structurally normal chromosomes moves to the opposite
poles along with one of the translocated ones. Meiotic products are duplicated
and deficient for different regions; therefore, gametes are non-functional.
Adjacent-1
segregation: Segregation of
nonhomologous centromeres during meiosis in a reciprocal translocation
heterozygote such that unbalanced gametes with duplications and deficiencies
are produced, as opposed to alternate segregation and adjacent-2 segregation
Adjacent-2 Segregation. Another kind of segregation possible in a
translocation heterozygote. In this case also, one normal and one translocated
chromosomes move to the same pole; but in such segregation, homologous
centromeres migrate to the same pole. Gametes are also inviable for the same
reason (as mentioned in the adjacent-1). Since Mendel’s second law still
applies to different paired centromeres, the possibility that the homologous
centromeres move to the same pole is almost negligible. Thus, this is a rare
event.
Adjacent-2
segregation: Segregation of
homologous centromeres during meiosis in a reciprocal translocation
heterozygote such that unbalanced gametes with duplications and deficiencies
are produced, as opposed to alternate segregation and adjacent-1 segregation
Admixture Gene flow
between genetically distinct populations of the same species.
A-DNA: The dehydrated form of right-handed
helical DNA obtained under non-physiological conditions
Adult Resistance. A type of plant resistance that is identified in
mature plants and is difficult to identify in seedlings.
Adult resistance:
Resistance not
expressed at the seedling stage; it increases with plant maturity (mature-plant
resistance or age resistance); generally attributed to horizontal resistance
Advanced intercross line
population
A population developed by intermating the individuals of F2 and subsequent
generations from a suitable cross.
Adventitious Embryony. A form of apomixis that leads to the production of
seeds without a sexual process.
Adventitious
embryony: A condition in a
seed in which the embryo arises from somatic rather than reproductive tissue;
the development of a diploid embryo from nucellary or integumentary tissue
(sporophyte tissue)
Aerobic Respiration. A process requiring O2 by which organisms generate
energy from ingested organic molecules.
Aerobic Rice. A new concept aimed at reducing water requirement in
rice production through developing a variety that can survive moderate drought.
Genetically engineered novel trehalose accumulation pathway in rice can
confer drought tolerance.
Aggressiveness. A measure of pathogenicity. It is used to describe the
capacity of a parasite to invade and grow in its host plant and to reproduce on
or in it. Aggressiveness and non-aggressiveness in the pathogen are the
counterparts of horizontal susceptibility and horizontal resistance in the
host, respectively. It maywell involve enzyme dose (dosage effect) and
switching on and off of enzyme action.
AFLP primer A primer having
the adapter sequence plus 1–3 arbitrary nucleotides at its 3' end.
Agricultural
Biotechnology: A range of tools,
including traditional breeding techniques, that alter living organisms, or
parts of organisms, to make or modify products; improve plants or animals; or
develop microorganisms for specific agricultural uses. Modern biotechnology
today includes the tools of genetic engineering.
Agricultural Output. A function of the kind and intensity of input use.
Agrobacterium rhizogenes: A species of Gram
-negative, rod-shaped soil bacteria, often harbouring large plasmids, called Ri
plasmids; it can cause a tumorous growth known as hairy
Agrobacterium tumefaciens: A bacterium that
causes crown gall disease in some plants; it infects a wound, and injects a
short stretch of DNA into some of the cells around the wound; the DNA comes
from a large plasmid the Ti (= tumorinduction) plasmid
Agrobacterium: A type of
soil-inhabiting bacteria that is capable of introducing DNA from plasmids in
the bacteria into the genome of plant cells. Often used in the genetic
transformation of plants.
Agrobacterium-mediated transformation: Agrobacterium is the generic name of soil bacterium
that frequently causes crown gall in many plant species; besides A. rhizogenes,
A. tumefaciens is one species that is most used in DNA transfer
by manipulating the Ti (tumor inducing) plasmid that is harbored by these
bacteria
Aids to Selection. Techniques used to enhance the efficiency of
selection. For example, the creation of epiphytotic condition helps determine
disease reaction among individuals of a segregating population in a
disease-free environment.
Albinism. A condition of absence or marked reduction of
pigments. Affected plants are characterized by the absence of chlorophyll in
the leaves. In humans, the affected persons have a very light skin in addition
to white hair and pink or red eye colour (because of the reflection of retinal
blood vessels). A recessive albino gene controls the condition.
Alien addition
line: A line (strain)
of plants with one or more extra chromosomes of an alien species
Alien chromosome
transfer: Cytogenetic
methods that facilitate the transfer of individual chromosomes from one species
to another
Alien chromosome:
A chromosome from
a more or less related species transferred to a crop plant
Alien gene
transfer: The transfer of
genes between species or genera by different means
Alien germplasm: Genes introduced from a wild relative
or nonadopted species
Alien species: An organism that has invaded or been
introduced by man and is growing in a new
Alien
substitution line: A line of plants
in which one or more alien chromosomes from a certain donor species replace one
or more chromosomes of recipient species
Alkylating Agent. A chemical agent that can add alkyl groups (e.g., -
CH3 or C2H5) to another molecule. Many mutagens act through alkylation. For
example, EMS (ethyl methane sulphonate) adds ethyl groups more specifically to
O6 position of guanine (in the DNA) and causes mutation through GC to AT
transition.
Allele Frequency. A measure of the commonness of an allele in a
population. The proportion in which an allele of a particular gene occurs in a
population is called allele or gene frequency.Allele. Also
called allelomorph. It is one of a pair or series of forms of a gene, which
arealternative in inheritance because they are situated at the same locus in
homologouschromosomes. It is a member of a specific gene pair. It may be
identical or dissimilar.If they are dissimilar, the use of alternative forms of
a gene is appropriate. One canexpress it by saying that there is a gene,
phonetically called a “see” gene, with allelesC and c. The
members with respect to this gene can be CC, Cc or cc.
Individualsrepresented by CC or cc are said to be containing
similar or identical alleles or genes.The term alleles or genes are used
interchangeably with respect to this gene pair only.Notice that although
different alleles of a gene pair can produce different effects, theyobviously
both affect the same character. Thus an allele, which may be any oneamong many
possible variant forms of a gene, results ultimately from mutation.
Allele frequency:
A measure of the
commonness of an allele in a population of alleles
Allele mining: An approach to access new and useful
genetic variation in crop plant collections; it focuses on the detection of
allelic variation in important genes and/or traits within a germplasm
collection
Allele: One of several alternate forms (DNA
sequences) that resides at the same locus on the chromosome and controls the
same phenotype (although with potentially differing effects).
Allele: One of the different forms of a gene
or DNA sequence that can exist at single locus.
Allele-specific oligo: In the case of Illumina Golden
Gate assay, two ASOs are used for each SNP locus; the 3' region of an ASO is
complementary to the sequence on the 3' side of the SNP locus, and its 3'
terminal base is complementary to one of the two alleles at the SNP locus.
Allele-specific PCR Selective
amplification of only one of the alleles at a SNP locus.
Allelopathy. A general term used for the secretion of chemical
messengers, whichprovide a competitive advantage for one species against
another in the association.Also called antibiosis.
Allelotyping Estimation of
the relative abundance of alleles of a SNP locus in a pool of DNA samples.
Allergen: A substance, usually a protein, that
can cause an allergy or allergic reaction in the body.
Allodiploid: Cells or individuals in which one or
more chromosome pairs are exchanged for one or more pairs from another species
Allogamy. Cross-fertilisation (allomixis).
Allogamy: Alternative term for
cross-pollination.
Allohaploid: A haploid cell or individual derived
from an allopolyploid and composed of two or more different chromosome sets
Alloheteroploid: Heteroploid individuals or cells whose
chromosomes derive from various genomes
Alloplasmic Line. The nucleo-cytoplasmic combination resulting after the
substitution ofthe genome of a species into the cytoplasm of an alien species.
The parental typehaving its own cytoplasm is called an euplasmic line.
Alloplasmic: An individual having the common nucleus,
but an alien cytoplasm (E.g. alloplasmic rye containing a wheat cytoplasm);
usually leads to meiotic disturbances and sterility
Alloploid (or
allopolyploid): An individual
with somatic cells that contain more than two sets of chromosomes, each of
which derives from a different species
Alloploidy. A situation wherein the individual contains
genetically different sets ofchromosomes, for example, from two or more
species. If two distinct species arehybridised, and the chromosome complement
of the resulting hybrid is doubled, theresult is the merging of the two species
into a new amphidiploid species. This isexemplified by N. digluta (2n=72),
which can be synthesized artificially by doublingthe chromosome complement of
interspecific hybrid between N. tabacum (2n=48)and N. glutinosa
(2n=24). Among various types of polyploidy, alloploidy has been themost
important in the ancestry of cultivated species. It provides a mechanism
fordirect speciation. A large portion of the cultivated species, possibly as
many as half(and 70% of the grasses), is alloploids. Induced alloploidy has
found an even smallerplace in practical breeding than autoploidy breeding.
Principles that govern thesuccess remain the same in both auto- and alloploidy
breeding (see polyploidy).However, induced alloploidy can be used to (a)
establish phylogeny of a polyploidspecies, (b) produce new plant genotypes, (c)
facilitate transfer of genes from relatedspecies, and (d) facilitate transfer
or substitution of individual chromosomes or pairsof chromosomes.
Allopolyploid. A polyploid that contains sets of dissimilar genomes
having been derivedfrom two or more distinct taxonomic species. As the genomes
are different, thepolyploid is also called hybrid polyploid. As it combines
complete chromosome setsfrom two or more species, it is sometimes called
amphidiploid. In general, alloploidscombine in more or less blending fashion
the characteristics of the species fromwhich they are derived. They have
generally increased vigour and have a high degreeof fertility and stability
compared to their diploid parents. The high degree of fertilityand stability of
the naturally occurring alloploids is because of regular bivalentformation at
meiosis. Since different genomes are highly divergent, thus pairingoccurs only
between homologous chromosomes belonging to identical genomes. Thusfor
practical purpose, there are only two chromosomes of each kind in the
alloploids.There are, however, many exceptions to this generalization. For
example, Ph genepresent in the long arm of 5B chromosome ensures
bivalent formation in bread wheat.
Allopolyploid: Plants with more than two sets of
chromosomes that originate from two or more parents; the sets contain at least
some nonhomologous chromosomes
Allosome: A chromosome deviating in size, form,
or behaviour from the other chromosomes autosomes), such as the sex chromosome
or B chromosome
Allosomes. Accessory chromosomes that differ from the rest
chromosomes (autosomes)in shape, size, and other attributes.
Allosteric
transition: A change from one
conformation of a protein to another conformation
Allosteric: An enzyme whose activity is altered
when its structure is distorted by an organic compound at a non-substrate site
Allosubstitution:
The replacement of a chromosome or chromosome arm by an alien chromosome or
chromosome arm
Allosyndesis. Pairing between chromosomes belonging to different genomes.
Allozymes. Allelic forms of enzyme loci that can be
distinguished by electrophoresis.
Allosyndesis: Chromosome pairing of completely or
partially homologous(homoeologous) chromosomes
Allotetraploid (syn amphidiploid): A
plant that is diploid for two genomes, each from a different species
Allozymes Variants of an
enzyme encoded by different alleles of the same gene.
Alternate Hypothesis. The conclusion drawn after rejection of the null
hypothesis (Ho).It is denoted by H1. If sample result fails to substantiate the
null hypothesis, it isconcluded that something else is true; this conclusion is
referred to as alternatehypothesis. (Also see null hypothesis).
Alternate Segregation. The passage of both normal chromosomes to one pole and
bothtranslocated chromosomes to the other pole in a translocation
heterozygote(reciprocal). As there is no net loss or gain of hereditary
materials, gametes are 100%functional.
Alternate
segregation: At meiosis in a
reciprocal translocation heterozygote, the segregation of both normal
chromosomes to one pole and both translocated chromosomes to the other pole,
giving genetically balanced gametes, or segregation of centromeres during
meiosis in a reciprocal translocation heterozygote such that genetically
balanced gametes are produced
Alternation of
generation: The alternation
of two or more generations, reproducing themselves in different ways (i.e., alternation
of gametophyte and sporophyte stages in the life cycle of a plant)
Alternation of Generations. The alternation of gametophytic and sporophytic stages
inthe life cycle of a plant.
Alternative
disjunction: The distribution
of interchange chromosomes at anaphase I of meiosis is determined by their
centromere orientation; in the case of alternative disjunction, chromosomes
located alternatively in the pairing configuration are distributed to the same
spindle pole
Alternative
splicing: Formation of diverse
mRNAs through differential splicing of the same RNA precursor; it may result in
proteins with different composition of amino acids, or it may involve just the
length of 3′ UTR; a reason for alternative/differential splicing is base
modification during RNA editing causing a change in slice sites
Aluminium Toxicity. A form of abiotic stress limiting crop production in
acid soils. Theproblem is particularly serious in strongly acid subsurface soil
horizons (pH<5.5) thatare difficult to lime. Aluminum (Al) toxicity
negatively affects growth of both rootand shoot. The root growth reduction may
stem from restricted absorption of waterand nutrients, and ultimately causes
yield reduction in such a problem soil. Undersuch a situation, use of tolerant
cultivars may be a satisfactory solution to thisproblem. Use of tolerant
genotypes and breeding of crops for Al tolerance is a reliableapproach to
enhance production on acidic soils. This requires a rapid and
effectivetechnique to discriminate between tolerant and sensitive genotypes.
There are severalscreening methods for Al tolerance such as solution, sand and
soil cultures, root regrowthand hematoxylin staining techniques, and field
screening. Selection ofseedlings in hydroponic assay has been used as a rapid
screening method to screen foraluminum tolerance in several crops. Hematoxylin
staining and root re-growthtechniques are also frequently used techniques
because they have produce consistentresults. In addition, the results obtained
with solution culture screening methodcorrelate positively with those obtained
using field screening, showing that thismethod could be representative of what
happens in the field. Hydroponic assayincluding hematoxylin staining has been
recommended to identify Al tolerantgenotypes in several crops. The reaction of
hematoxylin with Al–stressed roots hasbeen used by several researchers in
different crop species such as wheat, soybean,maize, peas, pigeonpea, and the
like.
Amaranthus Albumin Potato (Chakraborty et al. 2000).
A transgenic potato
containinga gene (AmA1) for a highly nutritive protein from Amaranthus
hypochondriacus. Thepotato so-obtained has 35-45% more protein, improved
protein quality (5-8 foldhigher essential amino acids) and tuber yield up to
3-3.5 fold with no evidence ofallergens.
Amber Codon. A triplet of bases (UAG) that stops translation
of genetic message from apart of DNA. It is also called chain (polypeptide)
terminating codon. The two otherstop codons are opal (UGA) and ochre
(UAA) ones.
Amber codon: Amber suppressor mutation that changes
anticodon of amino acid-carrying tRNA
Amber Suppressor. A mutant allele encoding a tRNA whose anticodon is
altered in sucha way that that the tRNA fails to stop translation (that is, it
inserts an amino acid) atthe site of an amber codon.Ameiosis. The
failure of or no meiosis. Meiosis is replaced by a mode of nuclear divisionthat
does not involve a reduction of the chromosome number.
Ameiosis: The failure of meiosis and its
replacement by nuclear division without reduction of the chromosome number
Ameiotic
parthenogenesis: Parthenogenesis
in which meiosis has been entirely suppressed amino acid, usually resulting in
an elongated protein
Amensalism. A kind of inter-species interaction in which one is
inhibited but the otherremains unaffected.
Amino Acid. A peptide; the basic building blocks of proteins (or
polypeptides). It ischaracterized by the presence of an amino group (-NH2) in
addition to a carboxylgroup (-COOH) and a side-chain (R). The side-chain (R),
which is bound to the alphacarbon, is different in each amino acid. Because of
the simultaneous presence ofacidic (carboxyl) and basic (amino) groups, amino
acids have both + and – chargesand are therefore amphoteric molecules or
zwitterions. Glycine is the simplest aminoacid. The two
sulphur-containing amino acids are cysteine and methionine, which aredeficient
in proteins of legumes. Cereal proteins have in general low lycine content
inthe protein.
Amino acid: A building block of proteins. Each
protein consists of a specific sequence of amino acids (with the sequence of
amino acids determined by the sequence of the underlying DNA). There are 20
types of amino acid molecules that make up proteins.
Amino acid: Any of a class of 20 molecules that
are combined to form proteins in living things. The sequence of amino acids in
a protein and hence protein function is determined by the genetic code
Aminoacyl-tRNA: A tRNA molecule covalently bound to an
amino acid viaan acyl bond between the carboxyl group of the amino acid
and the 3′-OH of the tRNA
Amitosis. Nuclear division by a process other than mitosis. In
this case, direct nucleardivision takes place.
Amitosis: Nuclear division by a process other
than mitosis
AMMI Model (Gauch and Zobel 1996). Additive Main Effects and MultiplicativeInteraction; a
statistical model for megaenvironment analysis. It is based on subdividinga
region into several relatively homogeneous megaenvironments andbreeding and
targeting adapted genotypes for each megaenvironment. AMMI analysisof regional
data can help in controlling errors and gaining accuracy. Results with
thismodel indicate that a small and feasible number of megaenvironments often
suffice toexploit useful interactions and increase yield by growing a specific
genotype in aspecific megaenvironment. AMMI analysis is helpful in assigning a
genotype to lowproductivity environments (which are prone to large errors,
minimize genotypicdifferences, and have less repeatability of genotypic
performance). Thus planting thewinning genotype in each megaenvironment
maximizes the yield; and planting thegenotype that wins in each megaenvironment
is helpful in assigning each area to theappropriate genotype recommendation.
Therefore, identifying megaenvironments andtargeting genotypes are interwoven and
interrelated.
Amphidiploid
(amphiploid): An alloploid
with the complete chromosome complements of two diploid species.
Amphidiploid (Clausen et al. 1945). An alloploid derived from combining entirechromosome
sets from two or more diploid species that are separated by barriers ofhybrid
sterility. Thus it contains distinct genomes in duplicate, that is, two copies
ofdifferent genomes (for example, AABB or AABBDD). It is more
stable meioticallythan autoploids owing to regular bivalent formation at
meiotic prophase. In general,polyploidy has the effect of broadening the
potential base of variation by increasingthe number of genes that can mutate.
Amphipathic. Of a molecule having both a hydrophilic and a
hydrophobic region.
Amplicon: The DNA segment
amplified by PCR.
Amplification. The production of many DNA copies from one master
region of DNA.
Amplification: An increase in the number of copies of
a specific DNA fragment; can be in vivo or in vitro.
Amplified fragment length
polymorphismIt
involves digestion of genomic DNA with two restriction enzymes, ligation of
appropriate adapters to the fragments, selective amplification of a much
smaller set of these fragments by using AFLP primers, and the separation of the
PCR products by denaturing polyacrylamide gel electrophoresis.
Amplified
fragment length polymorphisms (AFLPs): Polymorphic DNA fragments are amplified through PCR procedure;
their differences are used for genotype identification and linkage studies
Anaerobic glycolysis. Degradation of glucose into lactic acid in the absence
of oxygen,yielding two molecules of ATP.
Analysis of
variance (ANOVA): A statistical
method that allows the partitioning of the total variation observed in an
experiment among several statistically independent possible causes of the
variation; among such causes are treatment effects, grouping effects, and
experimental errors
Analysis of Variance. A statistical procedure of partitioning the total
variation intovarious components owing to contributing causes. The two main
objectives ofanalysis of variance are: (a) it helps in sorting out variance due
to different sources,and (b) it provides a basis for the test of significance.
Anaphase
separation: The disjunction
of the chromatids of each chromosome during mitosis and anaphase II of meiosis
or the separation of chromosomes in anaphase I of meiosis
Anaphase. An intermediate stage of nuclear division during which
chromosomes arepulled to the poles of the cell.
Anchored ISSR primer: In the case of
ISSR, the primer has a microsatellite sequence plus a short (usually, two
nucleotides long) arbitrary sequence either at its 3' or 5' end.
Androdioecious: Describes a species having male and
hermaphroditic flowers on separate individuals
Androecious. Of plants having only male flowers.
Androecium. The male reproductive organ of a plant; the stamens of
a flower takencollectively.
Androecium: A collection of stamens that form the
male reproductive organs of flowering plants
Androgenesis (Guha and Maheshwari 1966). In vitro genesis
of a plant from anthers ormicrospores. The resulting individual is a haploid.
The method was first used inDatura innoxia for the production of haploid
individuals.
Androgenesis: Development of a haploid embryo from a
male nucleus
Aneuhaploid: When the chromosome number deviates
from the haploid standard chromosome number of the species or individual
Aneuploid
reduction: Reduction of the
genetic variability by decreasing the chromosome number
Aneuploid. An individual whose somatic chromosome number (2n)
is not an exactmultiple of the basic number (x). Aneuploids arise when
normal gametes (n) arefertilised by abnormal ones (n+1, n-1,
etc.) and vice versa. Abnormal gametes mayresult due to non-disjunction during
meiosis. Asynaptic genes may cause formation ofunivalents that eventually
results in the formation of n+1 or n-1, gametes.
Somaticaneuploids occur as a result of mitotic non-disjunction or random
chromosome lossduring cell multiplication. Monoploids and triploids are another
source of aneuploids.Aneuploids are usually less vigorous and physiologically
less efficient than theirdiploid counterparts. This is because: (a) the balance
of chromosomes that isnecessary for a finely tuned cellular homeostasis,
carefully put together duringevolution, is grossly disturbed, and (b) any
deleterious recessive on the singleremaining chromosome becomes hemizygous and
may be expressed directly(monosomics, for example). Aneuploids (such as
nullisomics and monosomics) areordinarily viable in polyploids where homeologous
chromosomes appear to offsetmissing chromosome materials. Although
monosomics have been found in diploidlike maize, but there has been still a
debate on the diploid-like nature of this crop.Aneuploids such as
trisomics are usually not found in diploid species because theunbalance caused
by even a single extra chromosome is lethal. However, in a diploidspecies like
rice, where viable trisomics are found, trisomy usually exerts a profoundeffect
on morphology of the individuals. But in a “polyploid” species like breadwheat,
the degree of tolerance to repetitions of a particular chromosome(s) is so
greatthat even tetrasomics may be nearly indistinguishable from normal types.
In general,aneuploids are sterile (partly or even highly) and genetically
unstable. Owing tosterility, genetic instability and reduced physiological
efficiency, aneuploids havefound little if any direct use as marketing
varieties. However, some have been used inplant breeding for: (a) locating
genes on a particular chromosome, (b) transfer ofparticular chromosomes with
desirable genes from one variety to another, or evenfrom one species to
another, (c) mapping of genes on a chromosome, and (d)facilitating production
of hybrid varieties in barley (balanced tertiary trisomics during
Aneuploid: A cell or organism whose nuclei
possess a chromosome number that is greater or smaller by a certain number than
the normal chromosome number of that species; an aneuploid results from
nondisjunction of one or more pairs of homologous chromosome. An individual
with a chromosome number that is not the exact multiple of the basic number for
the species.
Aneuploidy. A situation wherein individuals or cells have
chromosome number, notexact multiple of the basic number (2n ± a few chromosomes).
Angstrom. A unit of length (usually wave length of radiation
energy such as X-ray).Numerically 1Å = 10-10m = 0.1nm (nanometer) = 0.0001m
(micrometer).
Anisoploid. A mixture of diploid, triploid, and tetraploid plants
obtained with seedharvested from a mixture of diploid and tetraploid plants.
Anlage. A
German word that appeared in Mendel’s original paper – Experiments in
planthybridisation – for the hereditary factor (now called the gene).
Annealing. Spontaneous alignment of two single DNA strands to
form a double helix.This property has been used to unravel a number of cellular
mysteries.
Annealing: Formation of double-stranded nucleic
acid from single stranded forms.
Annidation. See Ludwig theorem.
Anther culture: Culturing of anthers containing pollen
or of single pollen grains; the method is used for the production of haploid
plants, for the production of doubled haploids (which are homozygous) after
spontaneous or induced rediploidisation
Anther. The
pollen-bearing portion of the stamen.
Anther: The terminal portion of a stamen of a
flowering plant; the pollen sacs containing pollen are borne on the anther
Anthesis. The process of dehiscence of the anthers or the period of pollen distribution.
Antibiosis. Antagonistic association in which one
organism has an injurious effect onnormal growth and development of another. It
is a true mechanism of insectresistance. It includes all those factors or
characters of a resistant plant that causeadverse effects on the insect life
cycle when the insect uses it for food. Antibiosis is aspecific resistance;
however, it is not always monogenic. The main effects ofantibiosis are to
retard growth and decrease the rate of reproduction of individualinsects. Four
possible physiological explanations were suggested by Painter (1951) toaccount
for all those adverse effects on insects that stem from feeding on
differentresistant varieties: (a) the deleterious effects of specific chemicals
including toxins,(b) food materials present but for some reason not available
to the host, (c) the lack ofspecific food materials in the parts of plants
eaten by the insects, and (d) the presenceof repellents that prohibit the use
of host by the insects leading eventually the insectsto starve and die.
However, in this context, two points (b & d) may not account for theadverse
effects associated with antibiosis. Whenever, it is used as a mechanism
ofresistance (as in alfalfa against certain aphid species), intense selection
pressure isexerted upon the insect population. Consequently, new biotypes of
insects developvery rapidly especially if the insect is primary or obligate
feeder on one crop.
Antibiosis: The phenomenon whereby a natural
organic substance secreted by one organism has an injurious effect on normal
growth and development of another organism when the two organisms are brought
together
Antibody. A protein (immunoglobulin) molecule, produced by the
immune system thatrecognizes a particular substance (antigen) and binds to it.
Anticodon. A nucleotide triplet in a tRNA molecule that aligns
specifically with aparticular codon in mRNA under the influence of the
ribosome, and thus facilitatesinsertion of an appropriate amino acid into a
growing polypeptide chain.
Anticodon: A triplet sequence of nucleotides in
tRNA that during protein synthesis binds by base pairing to a complementary
sequence, the codon, in mRNA attached to a ribosome
Antigen. A
molecule (usually a foreign one) that is recognized by antibody(immunoglobulin)
molecules. Generally, multiple antibody molecules can recognize agiven antigen.
Antimutagen. Any agent reducing the rate of spontaneous and/or
induced mutation.Antimutagens may act either as protective agents or promote
the repair ofpremutational lesions (e.g. photo-reactivation). Mutagens and
antimutagens arecounteracting factors.
Antimutator gene:
Mutant genes that
decrease the mutation rates
Antiparallel
orientation: The normal
arrangement of the two strands of a DNA molecule, and of other nucleic-acid
duplexes (DNA–RNA, RNA–RNA), in which the two strands are oriented in opposite
directions so that the 5′-phosphate end of one strand is aligned with the
3′-hydroxyl end of the complementary strand
Antipodal cells: Three haploid nuclei that are formed
during megasporogenesisin plants; all are located opposite the micropylar end
of an ovule
Antisense DNA: Noncoding DNA of one of the
double-stranded DNA, asopposed to sense strand DNA, which is the coding DNA
(i.e., which is transcribed as mRNA)
Antisense gene: A gene construct placed in inverted
orientation relative to a promoter
Antisense RNA Technology. A technology that utilises antisense RNA to
silenceundesirable genes, and thus causes post-transcriptional down regulation
of the geneactivity. Antisense RNA complexes with mRNA, thus making it (mRNA)
unavailablefor translation. Using this technology, ripening of the fruit has
been delayed by down18regulation of the fruit-ripening genes. In other words,
it can extend the shelf life ofimmediate biological products.
Antisense RNA. The RNA that is synthesised using antisense strand of
a DNA segmentas the template. Its base sequences are complementary to the mRNA,
which isproduced naturally using sense strand of DNA as the template.
Antisense RNA: A complementary RNA sequence that
binds to a naturally occurring (sense) mRNA molecule; in this way it thus blocks
its translation
Antisense: The complementary strand of a coding
sequence(gene); often an expressed copy of an antisense sequence is transformed
into a cell or organism to shut off the expression of the corresponding gene.
Antixenosis (Kogan and Ortman 1978). Plant characters that cause differentialoviposition
and habitation by the insects on the host plants. Antixenosis means thatthe
plant is avoided because it is an undesirable host.
AP Sites. Apurinic or apyrimidinic sites resulting from the loss
of a purine or pyrimidineresidue from the DNA.
Apogamy. Development
of an individual from a gametophytic cell (such as synergids orantipodal cells)
other than the egg cell without fertilisation. Such individuals arehaploids.
Apomixis. A naturally occurring way of asexual reproduction
through seeds. In thismethod, reproductive organs or related structures take
part but seeds are producedwithout fertilization so that resulting seed is
vegetative in origin. Such individualscontain a genome derived entirely from
the female parent (gynogenetic clone). Itproduces progeny that are clones of
mother, thus allowing the fixation of favourablegenetic combination. It is
inherited as one or two dominant Mendelian traits locatedon a recombinationless
chromosome segment. It is typically facultative. Apomicts aremostly polyploids
or segmental polyploids, suggesting that ploidy levels could be akey component
of the apomixis. Increased ploidy levels cause failures of normalmeiosis;
plants have to resort to this means of reproduction in order to maintain
itsperpetuality. Further genomic asynchrony in the hybrids between two related
specieshaving different reproductive conduct and timing may also be a possible
cause ofapomixis. Both dominant and recessive control of apomixis has been
observed. It hasa great potential vis-à-vis fixation of hybrid vigour and is
expected to be one of theintense areas of future research; however, transfer of
apomict gene to cultivatedspecies such as maize, bajra, wheat, and the like has
not been successful thus far. Thepossibility that apomixis and sexuality are
not alternatives has made it difficult toinduce apomixis in sexual diploids.
The phenomenon of apomixis (apospory) hasbeen recorded as the notorious one
since it deprived Mendel of being recognizedduring his lifetime in the past.
Apomixis: Asexual reproduction in plants
through the formation of seeds without fertilization (agamospermy).
Apomixis: Asexual reproduction in plants without
fertilisation or meiosis
Apoptosis: Programmed cell death (PCD); a process
in which cellular DNA is degraded and the nucleus condensed; then cell is then
devoured by neighbouring cells or phagocytes.
Apospory: The development of a diploid embryo
sac in some plants by the somatic division of a
Apostatic Selection. Selection for rare genotypes.
Approach Crossing. A technique of artificial crossing that involves
bagging ofemasculated inflorescence with the inflorescence of pollen parent.
The shaking of thebag daily helps disseminate the pollen to the stigma of
emasculated flower. It usuallyresults in a higher percentage of seed setting
because fresh pollen is shed over a longperiod of several days. It has been
successfully used in wheat and can also be used insmall grain and forage
grasses.
Arbitrary primed PCRA single
arbitrary sequence primer of 18–32 nt is used for amplification; the first two
PCR cycles are carried out at low stringency.
Archesporium. A cell or group of cells formed by mitosis of the
micro- and megasporemother cells.Arrow. The inflorescence of sugar cane.
The branch length of the panicle (inflorescence)reduces towards the apex giving
it a distinct arrow shape.
Artificial
chromosome: A chromosome
experimentally created and constituted, in addition to genetically coding DNA
sequences, by ligating origin of replication, autonomous replicating sequences,
and telomeric and centromeric sequences
Artificial Neural Network (ANN). A network of nodes or inputs (like neurons) that
are processed in a non-linear fashion to provide a meaningful output. It may be
used to predict total food-grain production in a specific year on the basis of
certain inputs orvariables such as fertilizer consumption, rainfall and other
weather parameters.
Artificial
selection: Plant selection
by human or agronomic means; it is the practice of choosing individuals from a
population for reproduction, usually because these individuals possess one or
more desirable traits
Ascertainment bias: A systematic
bias generated in a dataset by the manner in which the data were collected.
Ascospore. A sexual spore from certain fungus species in which
spores are found in a sac(fruiting body) called an ascus.
Asexual Reproduction. A mode of reproduction that excludes involvement or
union ofgametes or sex cells, that is, reproduction by somatic cells, tissues,
or organs. Theensuing individuals resemble almost exactly their parent.
Asexually propagatedspecies in commercial practice reproduce by vegetative
means; genetic segregationand recombination do not occur in the successive
clonal generations. These speciesare highly heterozygous due to gradual
accumulation of naturally occurring mutations.They have higher levels of
sterility due to constant disuse of sex. The clones of suchspecies, previously
known to be resistant to pathogens (viruses and mycoplasma) andpests, soon
become susceptible due to either mutation of resistant genes or
subsequentchanges in biotype composition of these pests and pathogens. This
occurs becausegenetic filter through meiosis is precluded in successive vegetative
generations. Thisfactor, at the same time, also provides a clue why such
species evolve in nature moreslowly compared to sexually reproducing ones as
genetic variation through Mendeliansegregation and recombination is not
generated.
Asexual
reproduction: A propagation
without formation of zygotes by sexual organs and genetic recombination; in
plants, there are two types of asexual reproduction: vegetative propagation (by
stolons, rhizomes, tubers, tillers, bulbs, bulbils, or corms) and apomixis (by
vegetative proliferation or agamospermy). The reproduction process that does
not involve the union of gametes.
Association mapping population: A large random
sample from a natural population. a
germplasm core collection, a collection of breeding lines or a population
derived from a set of multiparent crosses and used for AM.
Association
mapping: A
population-based survey of molecular marker analysis in order to identify
trait-marker relationships based on linkage disequilibrium; the association
between a pair of linked markers is also called linkage disequilibrium (LD) or,
less frequently, gametic disequilibrium
Association of
Official Seed Certifying Agencies (AOSCA): Established in1919 in the United States; it
sets minimum standards for genetic purity and identity and recommends minimum
standards for seed quality; its goal is to standardise certification
regulations and procedures internationally so companies compete less than one
set of standards
Associative
transcriptomics The analysis of SNP genotype data generated from
RNA-Seq data to detect marker–trait associations.
Assortative
mating: Occurs if the
plants mating resembles each other, with regard to some traits
Assortment. Matching or grouping of a chromosome with other
non-homologouschromosomes during cell division.
Asynapsis. Failure of pairing of homologous chromosomes during
meiosis I.Atavism. The sudden appearance of an ancestral character in
the progeny. It may be dueto a mutation in an otherwise “inactive” gene or to a
change in the position of thatgene (owing to inversion or translocation) or
even deletion of the regulatory gene.
Asynapsis: Chromosomes of meiosis I in which
pairing either fails or is incomplete
ATP. Adenosine
triphosphate. It is usually
used for energy storage in the living systems.It is synthesized mainly in
mitochondria and chloroplasts. The energy from thebreakdown of ATP drives many
important reactions in the cell. There is no obviousreason why ATP is better
suited for energy storage than GTP, CTP or UTP. Amongthe organic bases, the
purine molecule, adenine is simply a pentamer of HCN and ismost readily
synthesised. It may be that the relative simplicity of the synthesis ofadenine
makes ATP better suited for energy storage than any other triphosphate of
Nbases.
Augmented Design (Federer 1956). An experimental design used to evaluate eitherlarger
number of test genotypes or genotypes with small quantity of seeds.Assessment
of larger no. of genotypes is not possible with the most frequently useddesign
(RCBD) due to problems of soil heterogeneity. Similarly, lower quantity ofseeds
of test genotypes poses problems in their replication. Augmented design hasbeen
suggested to obviate these problems. The three proposed augmented designs
are:(1) Augmented Completely Randomized Design, (2) Augmented
RandomizedComplete Block Design, and (3) Augmented Latin Square Design. The
first of these ismost frequently used when seeds of test genotypes are small in
quantity, whereas thesecond is most fit under condition of larger number of
test genotypes. It is worthmentioningthat what RCBD does by replicating the
whole entries, augmented designaccomplishes the same by replicating only the
checks and thus saving the space.
Autoallopolyploid:
Cells or
individuals whose genomes show characteristics of both auto- and alloploidy
Autofluorescence Fluorescence due to some endogenous molecule, e.g., chlorophyll in
plants.
Autogamy. Self-fertilization.
Autogamy: Obligatory self-fertilisation
Autogenous
control: The action of a
gene product that either inhibits (negativeautogenous control) or activates
(positive autogenous control) expression of its gene coding
Autonomous
apomixis: Agamic seed
formation that does not depend on pollination
Autonomous Controlling Element. A genetic element that seems to have both regulatorand
receptor functions combined in a single unit. It enters a gene and causes
unstablemutation.
Autonomous Phenotype. A genetic trait in multicellular organisms in which
onlygenotypically mutant cells exhibit the mutant phenotype. Conversely, anonautonomous
trait is one in which genotypically mutant cells cause other
cells,regardless of their genotype, to display a mutant phenotype.
Autoploid (or
autopolyploid): An individual
with more than two complete sets of the basic number of chromosomes for the
species.
Autoploid: A cell or individual with genomes
characteristic of the species itself
Autopolyploid. An individual containing multiple copies of the same
sets ofchromosomes (AAA, AAAA, AAAAA, etc). Autopolyploids have usually
large stomatalsize, cell size, increased vigour, large flowers and fruits,
large seed size and otherplant parts compared to their diploid counterparts.
However, these diagnostics are farfrom universal; many autoploids may be weak
and lacking in vigour. This may be dueto the existence of an optimum level
of polyploidy. In most groups, this level seems tobe achieved at fairly low
levels of ploidy; but in some groups, octaploids or evenhigher polyploids are
still vigorous types. Autopolyploids are invariably reduced infertility and produce
fewer seeds than their diploid counterparts due to several meioticcomplexities.
Autopolyploid: A polyploid organism that originates
by the multiplication of single genome of
Autopolyploidization:
The occurrence of
doublings of chromosome number by failure of chromosomes to divide equationally
in a mitosis following chromosome replication
Autoradiogram. A pattern of dark spots in a developed photographic
film or emulsion,in the technique of autoradiography.
Autoradiography. A technique in which radioactive structures take their
ownphotograph when placed next to a film or photographic emulsion and thus
helping inlocating the radioactive compound within the cell.
Autoradiography: A technique that uses X-ray film to
visualize radioactivelylabeled molecules or fragments of molecules; used in
analysing length and number of DNA fragments after they are separated by gel
electrophoresis.
Autoreduplication:
Biological
systems that generate the template for their own reproduction and duplicate
themselves
Autosome: Any chromosome in the cell nucleus
other than a sex chromosome
Autosomes. Chromosomes aside from sex chromosomes.
Autosyndesis. Pairing between chromosomes that belong to identical
genomes. (Also seeallosyndesis).
Autosyndesis: The pairing of complete or partial
homologues of chromosomes
Autotetraploid. A cell having four similar sets of chromosomes (AAAA)
or an organismcomposed of such cells. Autotetraploids seem to be agriculturally
more importantthan any other autoploids. Because four is an even number, they
can have a regularmeiosis, but this may not always be the case. In general,
meiotic process is muchmore complex than of diploids, which involve partition
of four chromatids, one toeach of the four gametes. In an autotetraploid, five
genotypes are possible at eachlocus compared to only three in diploids (at
two loci, the no. of possible genotypes fortetraploids and diploids are 52 and
32, respectively; would you like to formulate theno. of possible genotypes in
hexaploids at two loci?). The expected segregation andassortment in tetrasomic
inheritance is much complex. Factors affecting gameticoutput in tetraploids
are: (a) the regularity with which tetravalents (quadrivalents) areformed, and
(b) the randomness of disjunction from quadrivalents, which dependsprimarily on
the distance between the kinetochore and the locus in question. Thoughseveral
types of pairing possibilities exit in autotetraploids, but the bivalent
andquadrivalent formation tend to be more frequent. Examples of naturally-occurringtetraploids
are potatoes, coffee, perennial rye grass, alfalfa, sweet potatoes, pea
nuts,and the like.
Autotetraploid: An autopolyploid with four similar
genomes; if a given gene exists in two allelic forms A and a, then
five genotypic classes can be formed: AAAA (quadruplex), AAAa (triplex),
AAaa (duplex), Aaaa (simplex), and aaaa (nulliplex)
Autotrophic. A term
referring to cells which are able to synthesize their ownmacromolecules and
obtain their energy from simple nutrient molecules suchammonia, carbon dioxide,
etc.
Average Effect (of
a gene substitution). The difference between
average effects of thetwo genes involved in the substitution
Average Effect
(of a gene). Mean deviation from the population mean of
thoseindividuals, which received that gene from one parent, whereas the other
gene of thepair under consideration came at random from the population studied.
Average effect of
a gene: The change in
mean value of the population produced by combining a gene with a random sample
of gametes from the original population.
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