Exam 2 Flashcards
The Key Equation
The equation relating the rate of genetic change resulting from selection to four factors.
The four factors of the key equation
Accuracy of selection, selection intensity, genetic variation, and generation interval
Rate of Genetic Change
Rate of change in the mean breeding value of a population. Also called the response to selection
True or false. Crossbreeding and Inbreeding are not transferable to offspring.
True
Accuracy of selection
A measure of the strength of the relationship between true breeding value and their predictions for a trait under selection
True or false. The higher the heritability the more accurate we are in selection.
True
Selection criterion
Information that selection decisions are based on. Also called predictions
What are some values that are apart of selection criterion?
EBV, EPD, phenotypic selection, and scientific guess
Selection intensity
A measure of how choosy breeders are in deciding which individuals are selected
If intensity is high assuming selection criterion are reasonably accurate…
parents should be a lot better than average, offspring should be extremely better than average, rate of change should be rapid
If intensity is low…
parents are about average, offspring will also be about average
Truncation selection
selection on the basis of a distinct division in the selection criterion above which individuals are kept and below which they are rejected. the more animals kept the lower the intensity
proportion saved
the number of individuals chosen to be parents as a proportion of the number of potential parents
effective proportion saved
in selection - a value that, when substituted for actual proportion saved reflects correct selection intensity
threshold traits
polygenic traits that are not continuous in their expression but exhibit categorical phenotypes. selection intensities tend to be small
true or false. the better the performance of a population in a threshold trait the smaller the selection intensity
true
true or false. The more thresholds you have the closer you are to a continuous trait
true
genetic variation
variability of breeding values within a population for a trait under selection
characteristics of a large genetic variation
selection is intense, selection criteria is reasonably accurate, the best animals are far superior to average, fast rate of genetic change
genetic interval
the amount of time required to replace one generation with the next
genetic trend
the change in the mean breeding value of a population over time
replacement rate
the rate at which newly selected individuals replace existing parents in a population
selection risk
the risk that true breeding values of replacements will be significantly poorer than expected
breeding value lag
over time the genetic trend in the offspring will be the same as the genetic trend of the sire, the amount of time that is required for this to happen is the breeding value lag
quanititative genetics
the branch of genetics concerned with influences on measurement of relationships among genetic prediction for and rate of change in traits that are or can be treated as quantitative
phenotypic value
measure of performance for a trait in an individual
genotypic value
effect of an individuals genes on its performance for a trait
enviromental effect
effect that external factors have on animal performance
population mean
the average phenotypic value of all individuals in a population
breeding value
the value of an individual as a genetic parent. important for selection
independent gene effect
the effect of a gene independent of the effect of the other gene at the same locus and the effects of genes at other loci
progeny difference
half an individuals breeding value - the expected difference between the mean performance of the individuals progeny and the mean performance of all progeny
gene combination value
the part of an individuals genotypic value that is due to the effects of gene combinations and therefore cannot be transferred from parents to offspring. cannot be passed to offspring. important for contribution to animal performance
gene combination value is not transferable to progeny, but has a great impact on individuals performance in
hybrid vigor and inbreeding depression
producing ability
the function of all factors that permanently affect an individuals performance potential. important for repeated traits
repeated trait
a trait for which individuals commonly have more than one performance record. ex. milk production, weaning wt, twining in sheep
what values are determined at conception
genotypic values, breeding values, and gene combination values
permanent enviromental effects
permanently impact the animals performance. combo of genetic and environment
temporary environmental effects
temporary impact on animals performance. purely environment
heritability
a measure of the strength of the relationship between performance and breeding values for a trait in a population
repeatability
a measure of the strength of the relationship between repeated records for a trait in a population
contemporary group
a group of animals that have experienced a similar environment with respect to the expression of a trait
trait ratio
an expression of a relative performance - the ratio of an individuals performance to the average performance of all animals in the individuals contemporary group
normal distibution
individual values tend to follow a set of distribution within a population. symmetric, bell shaped curve, vertical axis
mean
an arithmetic average
variation
differences among individuals within a population
standard deviation
an average deviation from the mean
flat curve =
large amount of variation
sharp steep curve =
less variation
68%
within one standard deviation
95%
within 2 standard deviation
99%
within 3 standard deviation
covariation
how two traits or values vary together in a population
positive covariation move in the…
same direction
negative covariation move in the…
opposite direction
what are the two aspects of covariation
direction and strength
correlation
a measure of the strength of the relationship between two variables
regression
the expected or average change in one variable per unity change in another
