Quantitative Genetics

Question 1

What is a difference between population genetics and quantitative genetics

Answer 1

Population genetics: discontinuous traits

Quantitative genetics: no discrete classes ie continuous distribution of phenotypes

Question 2

Examples of quantitative traits

Answer 2

Length and weight
Behaviour
Fecundity
In fact, most LH traits
Most fitness traits 
Colour pattern of guppies

Question 3

What is the equation for phenotypic variation

Answer 3

Phenotypic variation = Genetic variation + Environmental variation
Vp = Vg + Ve

Question 4

What are quantitative traits controlled by

Answer 4

multiple genes (i.e. polygenic)

Question 5

what is the equation showing the relationship between no. of genes and no. of genotypes

Answer 5

N genes =3^N genotypes

Question 6

Why are the metric effects of alleles not always easy to add up

Answer 6

If there is a dominant allele ie the phenotypic effect of a is masked by A

Question 7

What are the issues with the studying quantitative variation with molecular markers?

Answer 7

Markers do not reflect environmental variation
They only poorly reflect non-additive variation
Markers are single locus, most traits multi-locus

Question 8

What is broad sense heritability

Answer 8

Ratio of total genetic variance : phenotypic variance

H2 = VG/VP

Question 9

(heritability) why can not all genetic variation be selected

Answer 9

because of dominance and epistatic variance

Question 10

What is narrow sense heritability

Answer 10

Ratio of additive genetic variance : phenotypic variance

h2 = VA/VP

Question 11

What does h^2 determine

Answer 11

determines how well population can adapt

Question 12

What are the important points to remember when talking about heritability (h^2) and populations

Answer 12

The heritability estimate is specific to the population and environment you are analysing
The estimate is a population, not an individual parameter

Question 13

What does h^2 no indicate

Answer 13

Heritability does not indicate the degree to which a trait is genetic
Rather, it measures the proportion of the phenotypic variance of a trait that is the result of genetic factors

Question 14

What does T stand for

Answer 14

T is mean phenotypic value of the population

Question 15

What does Ts stand for

Answer 15

Ts is the mean value of the selected parents

Question 16

What does S stand for

Answer 16

S is called the selection differential

Question 17

What is the symbol for the ‘response to selection’

Answer 17

R

Question 18

What is R and it’s equation

Answer 18

R is the difference in mean phenotype of the parental and offspring generation
R=T’-T

Question 19

What is the equation for adaptive response

Answer 19

Adaptive response = strength of selection (S) x heritability (h^2

Question 20

How can a really uncommon recessive allele can contribute to a selective response

Answer 20

It it increases in frequency
After a population bottleneck
Founder event
Inbreeding

Question 21

What hides a populations phenotypic variation, and how can it be released

Answer 21

dominance and epistatic variance, which can be released through bottle necks by increasing the chance of recessive alleles being displayed

Question 22

If heritability of a selected trait is 0, what is selective response e.g large body size

Answer 22

0, even if only large organisms get to reproduce, there size is completely dependent on environmental variation, therefore there will be no change in size in their offspring