# L17 Quantitative Genetics 2 Flashcards

1
Q

For complex quantitative traits

A
• degree of resemblance within families is a function of the genetic basis of the trait
• but the phenotypic value of the offspring is NOT exactly equal to the mean value of the parents
• the resemblance between relatives can be formally calculated under the additive quantitative genetics model
2
Q

Level of relatedness

A

level of relatedness between individuals is expected to lead to some trait similarity

3
Q

Genetic covariance

A

trait similarity between relatives is formally calculated in terms of genetic covariance

4
Q

Heritability

A

proportion of genetic variance compared to the total variance is called heritability

• makes strong assumptions: linear decomposition of effects (G and E) and no covariation/interaction among them
• strictly population specific, which means that any change in allele freq change its value
5
Q

Response to selection

A

knowing the level of heritability allows us to predict the response to selection of a population across generations

6
Q

Variance

A

variance of a variable is a measure of the deviation of the observed values from the expected mean
- genetic values being fixed, genetic variance is due to randomness of allele frequency

7
Q

Covariance

A

covariance of two variables is a measure of the joint variability of two variables e.g. how the two variables deviate jointly from their expected mean
- in genetics, the covariance between individuals for a trait is directly proportional to their level of relatedness

8
Q

Degree of identity

A

IBD - estimated from pedigree of individual

IBS - determined from sequence data

9
Q

Covariance between parent and offspring

A

See onenote

10
Q

Covariance between genetic effects

A

see onenote

11
Q

Covariance between sibs

A

see onenote

12
Q

covariance between any relatives

A

see onenote

13
Q

Partitioning the phenotype variance among and within families

A

see onenote

ANOVA

covariance between individuals of a family is by definition the variance among families

14
Q

A

ratio of genetic variance and the total phenotypic variance e.g. metric of how much trait variation is due to genetics

15
Q

Narrow-sense heritability

A

how much of the phenotype variance can be immediately transferred to the next generation

16
Q

Experimental designs to measure heritability

A
1. identical twins or clones = provides an estimate within one generation using ANOVA-type framework
2. comparisons between pairs of parent and offspring = provides an estimate over two generations using a regression framework
3. response to selection = provides an estimate over two generation with very little effort (only based on the means before, during and after selection)
17
Q

Pairs of monozygotic twins

A
• provides direct estimate of total genetic variance

- no decomposition into additive and dominance effects, thus of limited interest to breeders

18
Q

Midparent/offspring regression

A

see onenote

• covariance between offspring and parent provides direct estimate of heritability
• parents only directly transfer additive value to offspring. dominance effect calculation requires precise knowledge of IBD probability
• covariance of P/O is thus an estimate of additive variance, leading to an estimate of narrow sense heritability
19
Q

Response to selection

A

see onenote

20
Q

Breeder’s equation

A

predicts how a population will respond to selection under the hypothesis of linear selection

21
Q

The heritability of a trait depends on

A
• the genetic architecture of the trait (number of loci, genetic effect, additivity/dominance)
• freq. of genotype in a population