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