Quantitative Genetics - L22-24

Question 1

What causes continual variation in quantitative phenotypes

Answer 1

1. genetic variation
   - large number of loci - smooth distribution of phenotypes
2. Environmental factors
   - if genetically identical raised in lab - phenotypic variation roughly normally distributes

Question 2

Va = additive genetic variance

Answer 2

component of genetic variance due to additive effects at each locus

• the contribution at a particular locus depends on allele frequency
  Va = 2pq(a^2) - if at a single locus
  if all loci - Vg =Va

Question 3

Vd = Dominance variance

Answer 3

component of genetic variation due to interactions of alleles at a locus

• not inherited as alleles at a locus are broken up in the next generation

Question 4

Heritability

Answer 4

proportion of phenotypic variance passed onto next generation

• properties of a population not an individual
• predicts response to selection

Question 5

how to get h2 from a graph of offspring trait value agains mid-parent trait value

Answer 5

the slope - so the gradient of the correlation

Question 6

What does it mean if h2 is much greater than 0

Answer 6

additive genetic variation is present for the trait

Question 7

what is the response to selection - how is it calculated

Answer 7

difference between mean value of offpsring of selected individuals and the original population mean

R=h2 x s

Question 8

What variance does stabilising selection reduce

Answer 8

Va

Question 9

Vm = mutational variance

Answer 9

measures phenotypic variance of trait added by new mutations per generations

• estimated from response to selection of an inbred line

Question 10

How is quantitative genetic variation maintained in natural populations even though directional and stabilising selection act to reduce it

Answer 10

1. mutation
2. selection to maintain Va - disruptive selection, balancing selection at an individual loci, antagonistic selection that may involve multiple loci

Question 11

genetic correlation

Answer 11

when change at one locus is associated with change at another - it is possible to select for separation of this correlation but difficult

Question 12

phenotypic plasticity

Answer 12

different phenotypes expressed from same genotype in response to environmental variation

Question 13

Maternal effects - non-genetic inheritance

Answer 13

1. maternally-derived factors in eggs/uterus
2. maternal care
3. trans-generational epigenetic effects
   4, Cultural transmission of behaviour

Question 14

Paternal effects - non-genetic inheritance

Answer 14

1. paternally-derived factors in sperm
2. paternal care
3. trans-generational epigenetic effects
4. cultural transmission of behaviour

Question 15

Genomic imprinting

Answer 15

differential expression of alleles at a locus according to their parent-of-origin

Question 16

Adaptive consequences of non-genetic inheritance

Answer 16

• sometimes crucial to survival - song learning
• parent could fine-tune offspring pehnotype in relation to current environmenal conditions
• may be from conflict - parent offspring or mother father
• may be deleterious or neutral