W6L2 Resemblance between relatives and heritability

Question 1

What is the purpose of quantitative trait variation

Answer 1

allows for a population of organisms a flexible response: environmental variation and changes in selection mechanism
#analysis of qualitative traits inheritance does not need molecular knowledge

Question 2

What is genetic covariance

Answer 2

• The level of relatedness between individuals is expected to lead to “some” trait similarity.
• This trait similarity between relatives is formally calculated in terms of genetic covariance.

Question 3

Heritability in quantitative genetic

Answer 3

The proportion of genetic variance compared to the total trait variance is called heritability.
- The heritability for a trait in a population can be measured measured within or across generations.

Question 4

Calculation of variance and covariation

Answer 4

Question 5

The degree of idendity

Answer 5

Two individual are identical by state (IBS) for a locus if they carry an identical allele for that locus.
Two IBS alleles are identical by descent (IBD) if the alleles were inherited from an identical (recent) ancestor without recombination.
-IBS is typically determined from sequence data
- IBD can be estimated from the pedigree/genealogy of the individuals

Question 6

The covariance value between genetic effect (additive and dominance)

Answer 6

Question 7

The covariance between siblings

Answer 7

Question 8

The covariant between relative

Answer 8

Question 9

The Covariation between parent and offspring

Answer 9

Question 10

From the modeling of the genetic effect

Answer 10

• We have developed a model of decomposition of the trait/phenotypic variance into genetic and environmental effects.
• The genetic effects were decomposed into additive and dominant components.
• The additive genetic value is the fraction of genetic value directly inherited by the offspring from one of the parent, irrespective of the other parent.
• The dominance genetic value depends on the probability of the two alleles to be IBD.

Question 11

Partitioning the phenotype variance among and within families

Answer 11

Question 12

Definition of heritability

Answer 12

Question 13

Problem with herebility calculation

Answer 13

makes strong assumptions: a linear decomposition of the effects (G and E) and no covariation/interaction among them.
- It is strictly population specific, which means that any change in allele frequency changes its value.

Question 14

Experimental designs to measure heritability

Answer 14

• Identical twins or clones : Provides an estimate within one generation using an ANOVA-type framework.
• Comparison between pairs of parent and offspring: Provides an estimate over two generations using a regression framework.
• Response to selection :Provides an estimate over two generation with very little effort (only based on the means before, during and after selection).

Question 15

Study with monozygotic twin

Answer 15

Easy to achieve in organisms that can be inbred of vegetatively propagated.
- Slightly rarer and very sought after in Human.
- It is the only design providing a direct estimate of the total genetic variance, making it the historic gold standard in medical genetics.
However, sharing a common environment breaks the assumption of no environmental covariance between individuals.
- No decomposition into additive + dominance effects, thus of limited interest to breeders.

Question 16

Midparent/offspring regression

Answer 16

The covariance between parent(s) and offspring (P/O) provides a direct estimate of heritability.
The parents only directly transfer their additive value to the offspring.
Dominance effect calculation requires a more precise knowledge of IBD probabilities.
- The covariance P/O is thus an estimate of the additive variance, leading to an estimate of narrow sense heritability

Question 17

The Response to selection

Answer 17