Lecture 3 - Sources of vairiation

Question 1

Mutation

Answer 1

Any change in DNA of an organism

Mutations is the ultimate source of all heritable variation in evolution

Question 2

What mutations are heritable?

Answer 2

Only mutations in reproductive cells (germline)

Question 3

What leads to mutation?

Answer 3

Replication is an imperfect process

Random errors can lead to mutation

Environmental effects can influence the rate of mutation byt cannot determine which mutations occur

Question 4

What causes spontaneous mutations?

Answer 4

DNA polymerase infidelity (base substitutions, indels)

Chemical instability of purine and pyrimadine bases

Chromosomal abnormalities likely result from errors in repairing double strand breaks in DNA

Transposable elements

Question 5

Luria Delbruck experiment

Answer 5

Experiment that shows mutation is random

Pate bacteria with bacteriophage (T1) that lise bacteria and prevent them from growing

Bacteria have to mutate to form resistance agains the bacteriophage

If the process was not random you would expect to get the same number of colonies on your plates

If was random you would expect to get a large variation of number of colonies on each plate

Question 6

Accumulation experiments

Answer 6

Mutations are allowed to accumulate in inbred lines over many generations and the number of mutations that have accumulated at the end can be used to estimate the mutation rate

Question 7

How do you model evolution under mutation?

Answer 7

Assume all HW conditions hold, except now we allow mutation to occur

Make assumptions about the mutation process

Start with current allele frequency

Introduce new mutations according to the mutation process

Calculate allele frequency in the next generation

Ask question about evolutionary dynamics under the force of mutation alone

Question 8

p

Answer 8

The frequency of A1 in the next generation

Question 9

p’ or p1

Answer 9

The frequency of A1 in the next generation

Question 10

delta p

Answer 10

Change in the frequency of A1 over one generation

Question 11

p (with an upfacing >)

Answer 11

The equilibrium frequency of A1 (i.e. when there is no change in frequency of A1)

Question 12

What is the equation for p’

Answer 12

p’ = p(1-u) + q(v) (they are greek symbols)

in which u is the rate of mutation and v is constant overtime

Question 13

What is the equation for the change in p

Answer 13

deltap = -pu + v - pv

Question 14

How big is the mutation pressure on the change in allele frequency on the order of mutation rate?

Answer 14

It is very small

Question 15

What is the long-term outcome of a gene evolving under reversible mutation?

Answer 15

The ratio of the backward mutation rate from A2 to A1 over the total mutation rate determines the long term dynamics of the population

Question 16

What is the dynamics of a gene evolving under equal reversible mutation rates?

Answer 16

Will eventually reach an equilibrium state

If the rates are equal then the allele frequency will be o.5

Question 17

What dynamics of a gene evolving under unequal reversible mutation rates?

Answer 17

Will reach an equilibrium that does not have an allele frequency of 0.5

Question 18

What does reversible mutation lead to?

Answer 18

A stable evolutionary equilibrium to be met

Question 19

What is equilibrium frequency?

Answer 19

The ratio of backward mutation rate over the total mutation rate

Question 20

Where does recombination occur?

Answer 20

Between genes on:

non-homologous chromosomes as a result of segregation

Homologous chromosomes as a result of crossing over

Question 21

Recombination

Answer 21

Process in which your parents mixed your grandparent’s chromosome pairs together

Question 22

What is the equation for the number of different genotypes that can be produced by recombination?

Answer 22

(r(r+1))/2)^n

where n is the number of loci and r is the number of alleles at each locus