terminologies 2

• genetic variation - differences in genetic makeup that exist among animals
• inbreeding - practice of mating closely related animals
• lethal gene - gene that causes the death of an animal, usually homozygous recessive
• linebreeding - mild form of inbreeding
• longevity - length of useful life
• penetrance - ability of gene's characteristic to develop under the conditions of a particular environment
• persistency - degree which character is maintained during longevity
• predicted transmitting ability (PTA) - two alleles that have different effects that are distinguishable in heterozygous individual
• progeny test - evaluation of an animal based on the performance and appearance of it's offspring
• alleles - different versions of the same gene
• codominant alleles - two alleles that have different effects but are both distinguishable in a heterozygous individual
• crossbreeding - crossing two different breeds
• dominant allele - one that determines the phenotype
• drift - change in allele frequence over time due to chance
• epistasis - one gene's expression prevents the expression of another
• fixation - loss of all alleles of a gene
• gene dropping - loss of alleles due to genetic drift
• genetic bottleneck - when population numbers are temporarily reduced to a level sufficient to maintain the diversity in that population
• genetic diversity - expressed in terms of percentage of genes that are polymorphic and/or heterozygous
• genome - total genetic makeup of an organism
• heterozygous - carrying two different alleles of a gene
• heterozygous advantage - a heterozygous genotype for a particular gene shows the highest relative fitness
• allele frequency - fraction of all the alleles of a gene in a population that are one type
• outcrossing - mating of two individuals of the same breed that are sufficiently related
• recombination - reciprocal exchange of portions of two homologous chromosomes during gamete formation
• heterozygous insufficiency - heterozygous genotype lacks sufficient gene product to have normal phenotype (equivalent to partial dominance)
• heterosis - crossing of two inbred lines yield progeny more healthy/vigorous than their parents (commonly used in plant breeding)
• linkage - how frequently two genes found on the same chromosome remain together during gamete (egg or sperm) formation