Lecture 12 /13: Quantitative genetics

Question 1

The Breeders Equation

Answer 1

R = Delta Z = h^2 * S

• R = Response to selection
• Delta Z = Change in mean value of a trait over one generation (from parent generation to offspring generation)
• h^2 = Narrow sense heritability
• S = The Selection Differential, difference in mean trait value
  before and after selection (difference between ZR and ZP)

Question 2

narrow sense heritability

Answer 2

h^2 =Va / Vp

where:

Vp = phenotypic variance (variance of the examined trait)

Va = additive variance = Vp - Ve

Ve = environmental Variance

Question 3

Long term effects of genetic covariances (3)

Answer 3

Genetic covariances may slow evolutionary responses or cause traits to temporarily evolve away from the optimum values.

• Genetic covariations may influence evolution of long periods of
  time
• Mutations with large effects on the phenotype may cause
  changes in the G matrix.

Question 4

Fisher’s geometric model (4)

Answer 4

-Says that mutations will be beneficial when they are mostly of small effect

-Ie when they cause only a small change in the phenotype

-Assumes that populations are close to optimum phenotype

-Was very popular until the 1980’s until more and more experiment evidence against it accumulated

Question 5

QTL (4)

Answer 5

-Quantitative trait locus

-physical location on a chromosome that influences a quantitative trait

-Spans many nucleotides

-Contains 1 or more of the genes controlling the trait

Question 6

Genetic (QTL) mapping (3)

Answer 6

-Can use genetic linkage maps to estimate the position and number of QTL genes controlling quantitative traits as well as the size of their effect on phenotypes

-Looks for linkages between genetic makers and phenotypes

-Helps explain phenotypic variation through linked genes