Exam 3 Flashcards
Population measure
Any measure applied to a population as opposed to an individual
Population parameter
A true population measure (as opposed to an estimated). Ex. Means, variances, and standard deviation; true correlations between traits
Sample statistic
An estimate of a populations parameter
Normal distribution
A statistical distribution that appears graphically as a symmetric, bell-shaped curve.
Mean
The arithmetic average
Variation
Differences among individuals within a population
Variance
(o^2)
A mathematical measure of variation
Standard deviation
(o)
A mathematical measure of variation that can be thought of as an average deviation from the mean. The square root of the variation
Variable
Any quantity that can take on different numerical values. All elements (except Mu) of the genetic model for quantitative traits are considered variables
Covariation
How two traits or values vary together in a population
Covariance
cov(X,Y)
The basic measure of covariation
Correlation coefficient
r
(x,y)
A measure of the strength of a relationship between two variables
Phenotypic correlation
r
(Px,Py)
A measure of the strength of the relationship between performance in one trait and performance in another trait
Genetic correlation
r
(BVx,BVy)
A measure of the strength of the relationship between breeding values for one trait and breeding values for another trait
Environmental correlation
r
(Ex,Ey)
A measure of the strength of the relationship between environmental effects on one trait and environmental effects on another trait
Regression coefficient
b
(y*x)
The expected or average change in one variable (Y) per unit change in another (X)
True value
An unknown, underlying attribute that affects animal performance. Examples include breeding value, progeny difference, gene combination value, producing ability, and environmental effects
Predicted value
A prediction of a true value. Ex EBV or BV; EPD or PD; MPPA or PA
Prediction equation
A mathematical equation used to calculate a predicted value based on phenotypic data
Heritability
h^2
A measure of the strength of the relationship between performance and breeding values for a trait in a population
Heritability in the broad sense
H^2
A measure of the strength of the relationship betel next performance (phenotypic values) and genotypic values for a trait in a population
Repeatability
r
A measure of the strength of the relationship between repeated records for a trait in a population
A measure of the strength of the relationship between single performance records and producing abilities for a trait in a population
Contemporary group
A group of animals that have experienced a similar environment with respect the expression of a trait. Typically perform in the same location, same sex, similar age, managed alike
Contemporary group effect
E
cg
An environmental effect common to all members of a contemporary group
Trait ratio
An expression of relative performance— the ratio of an individual’s performance to the average performance of all animals in the individual’s contemporary group
Key equation
The equation relating the rate of genetic change resulting from selection to four factors: accuracy of selection, selection intensity, genetic variation, and generation interval
Accuracy of selection
r. ^
(BV, BV)
A measure of the strength of the relationship between true breeding values and their predictions for a trait under selection
Selection intensity
(i)
A measure of how “choosy” breeders are in deciding which individuals are selected
The difference between the mean selection criterion of those individuals selected to be parents and the average selection criterion of all potential parents, expressed in standard deviation units
Genetic variation
o
(BV)
In the context of the key equation for genetic change, variability of breeding values within a population for a trait under selection
Generation interval
L
The amount of time required to replace on generation with the next
In a closed population, the average age f presents when their selected offspring are born
Rate of genetic change
Delta BV/t
The rate of change in the mean breeding values of a population caused by selection
Response to selection
The rate of change in the mean breeding value of a population caused by selection
Selection criterion
SC
An EBV, EPD, phenotypic value, or other piece of information forming the basis for selection decisions
Selection differential
The difference between the mean selection criterion of those individuals selected to be parents and the average selection criterion of all potential parents, expressed in units of the selection criterion
Truncation selection
Selection on the basis of a distinct division in the selection criterion (point of truncation) above which individuals are selected and below which they are rejected
Proportion saved
p
The number of individuals chosen to be parents as a proportion of the number of potential parents
Effective proportion saved
Pe
In selection— a value that, when substituted for actual proportion saved (p), reflects correct selection correct selection intensity
Closed population
A population that is closed to genetic material from the outside
Genetic trend
Change in the mean breeding value of a population over time
Phenotypic selection differential
S
The difference between the mean performance of those individuals selected to be parents and the average performance of all potential parents, expressed in units of the trait
Progeny test
A test used to help predict an individual’s breeding values involving multiple matings of that individual and evaluation of its offspring
Replacement rate
The rate at which newly selected individuals replace existing parents in a population
Selection risk
The risk that the true breeding values of replacements will be significantly poorer than expected
