Lecture 2: Quantitative Genetics 1

Question 1

Define ‘quantitative genetics’.

Answer 1

The study of the genetic and environmental components of traits that vary continuously.

Question 2

Define ‘qualitative traits’ and give examples.

Answer 2

Difference between phenotypes of two individuals can be explained by the difference in genotype at a small number of loci i.e. 1 or two e.g. blood groups, cat coat colour, colour vision.

Question 3

Define ‘quantitative traits’ and give examples.

Answer 3

Phenotypic difference between individuals is due to difference in genotype at a large number of loci e.g. weight, height.

Question 4

What is the phenotypic variance dependent on?

Answer 4

Phenotypic variance = genetic variance + environmental variance.

Question 5

What is genetic variance dependent on?

Answer 5

Genetic variance = additive genetic variance + dominance genetic variance + epistatic genetic variation.

Question 6

What are the problems with predicting the evolution of quantitative traits?

Answer 6

• Dominance
• epistasis
• environmental effects.

Question 7

Define ‘heritability’ and give its equation.

Answer 7

A measure of the degree of resemblance between relatives. H squared = additive genetic variance/ phenotypic variance. OR H squared = additive genetic variance/ (genetic variance + environmental variance).

Question 8

What is the ‘breeder’s equation’?

Answer 8

R = h(squared) x S
R = response to selection
h = heritability
S = selection differential.

Question 9

What is epistatic genetic variance?

Answer 9

Variation due to interactions among loci.

Question 10

Define ‘polygenetic inheritance’.

Answer 10

A trait is determined by a large number of different genes (resulting in high variation).

Question 11

What is the midparent?

Answer 11

The mean of the mother and father values.