AS 368 Exam 1 - Definitions

correlation

A measure of the relationship between two variables. the direction of the relationship

standard deviation (o)

measures the spread of the data, but in units that are more easily interpretable. square root of the variance. approximately 68% of observations should be within one standard deviation above and below the mean

broad-sense heritability

measures the strength of the relationship between phenotype and genotypic value. expressed as total genetic variance %

allele

different versions of the same gene

polygenic inheritance

most phenotypic traits are qualitative = phenotype exists in only two (pr possibly a few more) discrete, alternative forms

MPPA

most probable producing ability

P = u (mu) + G + E

basic genetic model for quantitative traits

additive (A)

both alleles contribute equally to the phenotype, follow mendelian inheritance

natural selection affects

both wild and domesticated species

breeding for recreational or companion animals

breeders select for end users

seedstock

breeding animals whose role is to be a parent or contribute to the next generation

distribution

normal distribution: the statistical distribution that appears graphically as a symmetric, bell-shaped curve. most quantitative traits have this

heterozygote

one-locus genotype containing functionally different genes

homozygote

one-locus genotype containing functionally identical genes

natural selection

organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success

no dominance

a form of dominance in which the expression of the heterozygote is exactly midway between the expressions of the homozygous genotypes

complete dominance

a form of dominance in which the expression of the heterozygote is identical to the expression of the homozygous dominant genotype

partial dominance

a form of dominance in which the expression of the heterozygote is intermediate to the expressions of the homozygous genotypes and more closely resembles the expression of the homozygous dominant genotype

populations

a group of organisms of the same species located in the same place and time

corrective mating

a mating designed to correct in their progeny faults of one or both parents

selection intensity

a measure of how "choosy" breeders are in deciding which individuals are selected

accuracy of selection

a measure of the strength of the relationship between true breeding values and their predictions for a trait under selection

EBV

estimated breeding value - based on information available at the time you make a selection decision

ETA

estimated transmitting ability

regression

estimates the expected change in an observation (Y) per unit change in a second observation (X) (slope of a line). used most commonly to predict breeding values, progeny differences, and producing abilities based on performance information

EPD

expected progeny difference

Mendel's Law of Independent Assortment

genes found on different chromosomes are sorted into sex cells independently of one another (during gamete formation, different pairs of alleles segregate independently of each other)

Genotype

genetic makeup of an individual

commercial producers

an animal breeder whose primary product is a commodity for public consumption

permanent environmental effect

an environmental effect that has a lasting effect on trait expression. will affect an animal's performance throughout that animal'f life

temporary environmental effect

an environmental effect that only affect trait expression for a brief period of time. are temporary and only cause a transient effect on an animal's performance

epistasis

an interaction among genes at different loci such that the expression of genes at one locus depends on the alleles present at one or more other loci. one gene locus masks the phenotype of another gene locus

Mendel's Law of Dominance

an interaction between genes at a single locus such that in heterozygotes one allele has more effect that the other

intermediate optimum

an intermediate level of performance that is optimal in terms of profitability and/or function

Phenotype

an observable category or measurable level of performance for a trait in an individual

population genetics

analyzes the amount and distribution of genetic variation in populations and the forces that control this variation

Trait

any observable or measurable characteristic of an individual (apperance or performance)

covariance

how traits vary together in a population. measured by covariance, correlation, and regression. the sum of the product of deviations of each individual value from their trait means, divided by the total number of observations

varience

comparing the variability of different traits and different values (P, BV) for a single trait

heritability

correlation between breeding values and phenotypic values for a trait in a population

heterozygousity

crossbreeding results from mating unrelated populations

Hardy-Weinberg equilibrium

if there are no forces to change gene and genotypic frequencies in a population, those frequencies won't change forces - selection, mutation, migration a population in equilibrium must be large and randomly mated

random drift

in small populations gene frequencies change by chance

homozygousity

inbreeding results from mating of related population

epistatic (E)

interaction between alleles; associated with different loci

chromosome

long strands of DNA and associated proteins

P

phenotypic value or performance of an individual animal for a trait

threshold traits

polygenic traits that exhibit categorical phenotypes

narrow-sense heritability

proportion of differences in performance for a trait that are attributable to differences in breeding value for that trait. expresses the percentage of genetic variance that is caused by additive gene action, Va

moderate (h^2 = 0.2-0.2)

related to "performance" or weighted traits

low (h^2 < 0.2)

related to fertility and survivability

high (h^2 > 0.4)

related to skeletal structure and carcass characteristics

artificial selection

replacement selection - selected individuals will contribute to the population culling - individuals will no longer contribute to the population

mating

selecting maes will be bred to selected females

individuals

selection acts upon the individual

sex-related inheritance

sex-linked - genes are inherited based on sex chromosome sex-limited - expression of a trait is limited to one sex sex-influenced - appear in both sexes, but is sex dependent

locus (loci)

specific location of a gene on a chromosome

gene

specific segments of DNA on a chromosome each animal has two copies of each gene, one from sire and dam

genetic variation

tends to be fairly fixed within a population. outbreeding can increase it somewhat, and inbreeding can have the opposite effect. selection in one direction over many generations will reduce genetic variation

G = BV+GCV

the additive genetic effect (or breeding value (BV)) and the gene combination value (GCV)

genetic intervals (L)

the amount of time required to replace 1 generation with the next

repeatability

the change in producing ability expected per unit change in phenotypic value. mathematically, the regression of producing ability on phenotypic value. it is the ratio of the variance of producing ability to the variance of phenotypic value

E

the environmental effect (nongenetic) on the individual's performance for the trait

progeny differences (PD)

the expected difference between the mean performance of the individual's progeny and the mean performance of all progeny

overdominance

the expression of the heterozygote is outside the range defined by the expressions of the homozygous genotypes and most closely resembles the expression of the homozygous dominant genotype

G

the genotypic value of the individual for the trait

breeding value (BV)

the sum of all the additive allele effects at all loci that affect a trait. can be transmitted from parent to offspring

Mendel's Law of Segregation

the two copies of a gene segregate from each other during transmission from parent to offspring (explains why we get half DNA from sire and half from dam)

simply-inherited trait

traits affected by a few genes

polygenic trait

traits affected by many genes

genetic drift

variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.

selection

which animals become parents, how many offspring they may produce, and how long they remain in the breeding population

gene combination value (GCV)

the part of an individual's genotypic value that is due to the effects of gene combinations (dominance and epistasis) and cannot, therefore, be transmitted from parent to offspring

producing ability (PA)

the performance potential of an individual for a repeated trait

u (mu)

the population mean or average phenotypic value for the trait for all animals in the population

random mating

absence of systematic mating scheme

factors affecting rate of genetic change

accuracy of selection, selection intensity, genetic variation, generation interval

prediction

accurate predictions come from large amounts of high quality data. can help us with selecting the best animals in a population at an early age. EBV, EPD, and MPPA

mean (u)

add up values from a population and divide by the total number of values. this determines the center or distribution

P = A + D + I + E

advanced genetic model for quantitative traits

environmental effect

The effect that external (nongenetic) factors have on animal performance

qualitative or categorical trait

a trait in which phenotypes are expressed in categories, "either or expression"

quantitative trait

a trait in which phenotypes show continuous (numerical) expression

dominance (D)

one allele is stronger and contributes to the phenotype interactions between alternative alleles at a specific locus

species

a set of populations that are reproductively isolated from other such population sets

variation (o)

differences among individuals within a population. source of genetic change