Mutation and variation Flashcards
(33 cards)
Define a mutation.
Any heritable change to genomic DNA.
Are changes to whole chromosomes possible, or simply to single bases?
Both are possible.
Recessive mutations typically cause what?
A loss of function.
Dominant mutations typically cause what?
A gain of function.
What do conditional mutations depend on in order to be expressed?
The correct environment.
What will lethal mutations do?
Kill the bearer in the homozygous condition.
Are there any constraints on mutation?
No, anything can happen.
What are the 2 views of evolution with respect to mutation?
- Neo-Darwinist = gradual accumulation of advantageous mutations improve the fitness of an organism
- Catastrophist = macro-mutations occur in regulatory gene sequences causing a cascade of multiple changes on other genes.
In the Neo-Darwinist theory of evolution, what kind of magnitude does each mutation have?
A small effect on evolution.
Mutation rate can be studied in different ways. Give 3 examples.
- Per cell cycle
- Per generation
- Per chromosome
Describe the experiment in mice used to assess mutation rate in loci per generation based on visible phenotypes.
- The reference population are all females that are homozygous recessive for different coat colours
- Cross these to wild type males
- Progeny are expected to be heterozygous at the marker (coat colour) loci
- Any other visible phenotypes are assumed to be mutations.
Mutation rate at each locus is very low, so you would expect the affect of mutation on variation to be very small. Why is this not the case?
The number of mutations is summed across all the genes, meaning the input to variation is considerable.
Mutations are only ever advantageous, deleterious or lethal. True or false?
False - they can also be neutral.
Who performed the famous mutation experiment on drosophila in 1972?
Mukai.
What was the point of Mukai’s experiment in 1972?
He allowed the accumulation of slightly deleterious mutations over generations at multiple loci to assess their impact on fitness.
How many chromosomes did Mukai include in his experiment?
3 - two autosomal and the sex chromosomes in drosophila.
Mukai used balancer chromosomes in his tester stock. Why?
They cannot recombine due to multiple inversions. As a result the wild type chromosomes are conserved when he bred the tester stock to a population of interest.
How did Mukai know which flies had the balancer chromosome?
He marked them with mutant dominant alleles so the balancer flies could be visibly identified.
Give an example of a dominant marker Mukai used to identify his balancer flies?
Curly wing.
How did Mukai ensure that all his flies were heterozygous at the balancer locus?
The dominant markers he used were lethal in homozygous condition.
When Mukai bred his balancer stock to a wild type population, what did the F1 inherit? Why was this important?
A balancer chromosome from one parent and a wild-type from the other. These two cannot recombine so any mutations on the wild type chromosome are conserved and accumulate.
Mukai performed a back-cross between his F1 and more balancer stock. What were the 3 possible genotypes in the F2?
- Heterozygous
- Homozygous wild-type
- Homozygous balancer (dead)
What did Mukai find as mutations began to accumulate in his flies?
Viability decreased.
Why does Mukai’s experiment serve as support for Neo-Darwinist theory of evolution?
All the lines he created responded in a similar way, with a decrease in viability, because they had similar numbers of mutations. In catastrophist theory, we would expect to see some lines as mutation free and some riddled by mutation.
