The branch of genetics concerned with influences on, measurement of, relationships among, genetic prediction for and rate of change in traits that are quantitative, or continuous, in nature (such as weight or height)
quantitative genetics
discrete traits controlled by a few alleles at one or a few loci and influenced little or none by the environment. traits such as coat color for which phenotypes can be classified into groups or classes.
qualitative traits
traits that have quantitative value, traits influenced by many alleles at several different loci that have a continuous expression and are effected by the environment
quantitative traits
a trait affected by many genes, no single gene having an override influence
polygenic trait
the ability of one allele to express its phenotype at the expense of the alternate allele; an interaction between genes at a single locus such that in heterozygotes one allele has more effect than the other.
Dominance
an interaction among genes at different loci such that expression of genes at one locus depends on alleles present at one or more other loci
epistasis
the effect that external (non genetic) factors have on animal performance
Environmental effect
an environmental effect that influences a single performance record of an individual, but does not permanently affect the individuals performance potential for a repeated trait
Temporary environmental effect
an environmental effect that permanently influences an individuals performance for a repeated trait
Permanent environmental effect
breeding effects that are consistently transmitted from parents transmitted from parents to progeny , the additive genetic worth of an animal relative to some base population, the worth of an individual as a (genetic) parent.
Breeding Value
predication of genetic value derived from the application of genetic theory and statistics to performance records; estimate of unknown breeding value.
Estimated breeding value
an estimate, or prediction, of how much better or poorer an individuals progeny will perform compared to the average of all individuals in the breed.
Expected progeny difference
a trait for which individuals commonly have more than one performance record
Repeated trait
the performance potential of an individual for a repeated trait, (milk production;wool production;racing ability)
Producing ability
any quantity that can take on different numerical values. all elements (except u) of the genetic model for quantitative traits - P, BV, E - are considered
Variable
a group of inter mating individuals; individuals that share a common gene pool. the term can refer to breed, an entire species, a single herd or flock, even a small group of animals within a herd or flock
population
The Basic Model
P=u+G+E p= phenotypic value u=the population mean G=genotypic value E=environmental effect
the value of a trait for an individual
genotypic trait
only effect that can be transmitted to the next generation; most important type of gene action controlling quantitative traits
Additive Gene effects
two genes effects that can not be transmitted to the next generation
dominance and epistasis
they reflect the value of each gene independent of the effects of other genes at the same loci and the effects of genes at other lcoi
independent gene effects
expected difference between mean performance of individuals progeny and mean performance of all progeny (assuming random mates)
Progeny Difference
is the part of an individuals genotypic value that is due to the effects of gene combinations and cannot, therefore, be transmitted from parent to offspring
Gene combination value
most common measure of variability in a population; used to describe how widely observations are distributed around the center of distribution
standard deviation
effect of a gene independent of the effects of the other gene at the same locus and effects of genes at other loci
independent gene effects
part of an individuals genotypic value due to effects of dominance and epistasis
gene combination value
performance potential of an individual for a trait that is measured more than once in its life
producing ability
half of individuals breeding value
progeny difference
type of gene action in which allele of a pair has an independent negative or positive effect on the phenotype, which is independent of gene effects at other loci
additive gene action
traits for which individuals commonly have more than one production record
repeated trait
basic genetic model for repeated trait
P=U+G+PE+TE
additive genetic merit of an individual as parent
breeding value
numerical measures associated with a sample
statistic
general term that describes how two traits or values vary in a population; correlation and regression are two specific measures of this
covariation
most useful measure of central tendancy
mean