Lecture 13- Quantitative genetics

Question 1

what is the quantitative model

Answer 1

way of quantifying complex genetic changes
P = mu + G + E
where mu=population mean, G = genotypic effects, E = environmental effects

Question 2

what contributes to G

Answer 2

additive variance, dominance variance, epistatic variance in interaction between genes

Question 3

what contributes to E

Answer 3

pure environmental effects and interactions between genes and environment

Question 4

how can you mathematically describe heritability

Answer 4

ratio of genetic variance / total phenotypic variance- value between 0 and 1 as phenotypic variance is always higher

Question 5

3 different ways of looking at heritability

Answer 5

analysis of parent-offspring correlations (correlation between average parent and sibling values for a trait)
sib analysis- based on variation among half- and full-sib groups
twin pairs- taking genetically identical organisms from the same litter

Question 6

3 issues with heritability estimates

Answer 6

assumptions, such as that 50% of the genome will be shared in siblings, may not be entirely true
genetic change is not accounted for
developmental age can impact traits and their expression

Question 7

what is deltaP, equation

Answer 7

genetic gain- average change in phenotypic value due to selection
h2 * i * Vp (phenotypic variance) where h is heritability and i is selection intensity

Question 8

how can breeding value of an individual be estimated

Answer 8

h2 (heritability) and the phenotypic difference between the individual and the population mean

Question 9

2 issues with using these esitmates in selective breeding, and how they can be fixed

Answer 9

differences between population heritability over time etc- can recalculate h2 periodically, or recalculate the value when combining populations

changing environmental conditions, which can change the estimate of deltaP, can recalculate h2 in different environments or use different breeding populations

Question 10

selection differential S

Answer 10

can measure total selection acting directly and indirectly on a trait- larger it is, the higher the mean shift

Question 11

how can genetic correlations be calculated

Answer 11

using a selective index, can plug in multiple traits and assign weights to each depending on their genetic correlation- can then look at a single trait taking into account others

Question 12

what is QTL mapping

Answer 12

identification of regions which impact a complex trait by identifying the loci which are correlated with it using recombination- ‘quantitative trait locus’

Question 13

how does QTL work

Answer 13

looking at recombination to map the locations of a specific trait
need large 1k+ sample sizes, due to low recomb rates
can use linear regression to look at correlations between changes at loci and phenotype