Signatures Of Selection

Question 1

Truncation

Answer 1

Only individuals in a population larger than a certain threshold can reproduce

Question 2

Negative selection

Answer 2

The most desirable trait remains and is dominant over the less desirable (bell curve graph)

Question 3

Positive selection

Answer 3

One trait increases in frequency as is desired

Skewed graph

Question 4

Balancing selection

Answer 4

There is equal frequency across all traits in a population

Question 5

What does a positive tajimas D result suggest?

Answer 5

Balancing selection or a bottleneck (more pairwise differences than segregating sites)

Question 6

What does a negative tajimas D result suggest?

Answer 6

Positive selection within the population (more segregating sites than pairwise differences)

Question 7

Types of quantitive traits

Answer 7

1. Continuous e.g. height
2. Meristic: phenotypes in discrete classes e.g. number of petals on flower
3. Discrete: trait either present or not

Question 8

What’s a liability value?

Answer 8

Traits that are threshold dependent
- need accumulation of genetic and environmental traits
- threshold same for individs but if relative have it then your chances of passing threshold higher
E.g. diabetes

Question 9

Phenotypic variation equation

Answer 9

Var (P) = Var (G) + Var (E)

Question 10

Broad sense heritability

Answer 10

H2 = Var(g)/Var(p)

- influence of genes on phenotypic trait

Question 11

Narrow sense heritability

Answer 11

h2= Var(a)/Var(p)

- how additive genes have influenced the phenotype

Question 12

The selection differential equation (truncation)

Answer 12

S = us - u
Us: the mean of the desire phenotype pop
U = the mean of the whole population

Question 13

The selection response equation (truncation)

Answer 13

R = u’ - u
U’ = the mean phenotype of the offspring 
u = the mean of the whole population.

Question 14

The realised heritability (truncation)

Answer 14

• h2 = R/S

Question 15

How to tell if the environment is the only driver in phenotype change between two environments (on a chart)

Answer 15

The change is the same across all genes

All lines change in the same way

Question 16

How to tell if there is a genotype x environment interaction changing phenotypes between states(on a chart)

Answer 16

The lines (genes) cross each other

Question 17

How to tell if there is conditional neutrality between states on phenotypes

Answer 17

Some of the genes appear to change between states but one or more dont change at all.

Question 18

How to map loci with recombinant inbred lines

Answer 18

Cross breed 2 parents with differing phenotypes = F1 intermediate
Let F1 self = F2
Let F2 inbreed
After many generations you can see all traits and choose the ones you want to select for
Make molecular markers to see what genes are the same for all chosen individs

Question 19

Describe interval mapping

Answer 19

Lander and Botstein (1989)
Uses estimated genetic map for the location of QTLs
Intervals are defined by ordered pairs of markers e.g. SNPs
Stats are used to test if a QTL is likely to be in an internal
Results displayed as LOD (logarithm of odds) scores
- high LOD suggests that the loci is present in that interval
No interactions between QTLs considered

Question 20

What is association mapping?

Answer 20

• alleles that cause disease phenotypes should be v low frequency in a pop
• however after a mutation recombination maintains linkage disequilibrium… the older the mutation the tighter the region
• cross parents with different 2 phenotypes
• see % of progeny that have mixed phenotypes (one from each parent)
  That % = map units and centimorgans for distance on chromosome from each other

Question 21

Describe landscape genomics

Answer 21

Sample individs on grid over a landscape and their genotypes for markers
Record the environment variables e.g. temp
Observe any correlations between environment and their markers to see if its a response to the environment

Question 22

Us

Answer 22

The mean of the desired phenotype in OG population (mean of cut off range)

Question 23

u

Answer 23

The mean of the whole OG population

Question 24

U’

Answer 24

The mean of the offspring population