Genetics and Plant Breeding: Key Terms and Concepts

Allele

alternative form of a gene at a locus

Breeding

genetic modification of living organisms

Chromosome

structural unit in the nucleus that carries genes in a linear order

Correlation

statistical measure of the degree to which two characters vary together

Cultivar

cultivated variety of a plant

Dihybrid

progeny of cross between parents that differ for the alleles at two loci

Diploid

individual with two sets of basic genome (2x)

Dominance

interallelic interaction at a heterozygous locus when one allele partially or completely masks the expression of another allele

Environment

external conditions that influence expression of genes of an individual

Fertilization

fusion of an egg and sperm to form a zygote

Gamete

sex cell produced by the female and male reproductive organs

Gene

basic unit of inheritance which is a sequence of DNA nucleotides that codes for a functional product of RNA or a polypeptide

Genetic marker

allele used to identify a gene, chromosome segment, or a chromosome

Genome

basic set of chromosomes of an organism

Genotype

genetic makeup of an individual

Genotypic ratio

proportions of different genotypes in a population

Germplasm

total of the genotypes that constitute a species

Haploid

cell or individual with half (n) of the somatic chromosome number

Heritability

portion of the phenotypic variation among individuals that is due to genetic differences among them

Broad-sense heritability

estimated from the ratio of the total genetic variance to the phenotypic variance

Narrow-sense heritability

estimated from the ratio of the additive portion of genetic variance to the phenotypic variance

Heterosis

condition in which a hybrid exceeds the performance of its parents for one or more characters

Mid-Parent heterosis

represents performance of the hybrid that exceeds the average performance of the parents per se

High-Parent heterosis

occurs when the hybrid performance exceeds that of the best parent

Heterozygous

different alleles are present at a locus on homologous chromosomes in a diploid or polyploid individual

Homozygous

identical alleles are present at a locus on homologous chromosomes in a diploid or polyploid individual

Hybrid

progeny of mating between genetically different parents

Inbred line

line produced by inbreeding that is homozygous and homogeneous

Inbreeding

mating of individuals that are related by decent

Line

progeny of an individual plant

Linkage

condition in which genes located on the same chromosome are inherited together due to their close proximity

Locus

position occupied by a gene on a chromosome

Mean

average of a series of observations

Meiosis

process that occurs in the female and male reproductive organs by which the chromosome number in somatic sells (2n) is reduced by one half (n) in the haploid gametes

Mitosis

process by which the nucleus of a cell is divided into two genetically identical nuclei

Mutation

heritable variation in a gene or in chromosome structure

Pedigree

record of the ancestry of an individual

Phenotype

appearance of an individual or group of individuals

Phenotypic ratio

proportions of different phenotypes in a heterogeneous population

Pollination

transfer of pollen from the anther to the stigma of the pistil

Probability

likelihood that an event will or will not occur

Qualitative character

character for which the phenotypic variation among genotypes is not continuous and cannot be separated into discrete classes

Recessive

condition of an allele whose expression is masked in the presence of a dominant allele at the same locus on a homologous chromosome

Recombination

formation of new combinations of genes as a result of the independent assortment that occurs in a heterozygous individual during meiosis

Resistant

characteristic of a plant that is capable of suppressing or retarding development of a pathogen or other injurious factor

Segregation

separation of allelic pairs and their distribution to different cells during meiosis

Strain

a group of similar and related individuals

Variance

statistical measure of the mean squared deviation of individual measurements from the overall mean of the measurements

Variety

subdivision of a species for taxonomic classification. Used interchangeably with the term cultivar to denote a group of individuals that are distinct genetically from other groups of individuals in the species

Zygote

cell formed from the union of female and male gametes