Evolution of the genome

Question 1

Evolution occurred through

Answer 1

genetic recombination (double strand break), gene conversion (heteroduplex joint repaired by excision of mismatch and then repair leading to extra allele), gene duplication and tandem repeats, transposable elements, split genes. DNA is dynamic and evolution will always occur

Question 2

tandem repeats

Answer 2

Moderately repetitive DNA consists of a number of types of repeated sequence. clusters At the lower end of the repeat scale come genes which occur as clusters of multiple repeats. These are genes whose products are required in unusually large quantities. Unequal crossover between sister chromosomes can see them expanded or contracted. very high mutation rights, because of the same sequence they easily misalign. A point mutation can give the replication machinery a chance to realign the strands and give rise to repeats with a mutation.

Question 3

gene duplication

Answer 3

The duplication of a gene results in an additional copy that is free from selective pressure. One kind of view is that this allows the new copy of the gene to mutate without deleterious consequence to the organism. This freedom from consequences allows for the mutation of novel genes that could potentially increase the fitness of the organism or code for a new function Another view is that both copies are equally free to accumulate degenerative mutations, so long as any defects are complemented by the other copy. This leads to a neutral “subfunctionalization” in which the functionality of the original gene is distributed among the two copies.

Question 4

Globin gene family

Answer 4

evolution of a second chain in globin by at 500m duplication followed by a mutation (alpha to beta), 350m transposition of alpha to chromosome 16, 200m point mutation leading to adult and foetal beta on 11, multiple duplications and mutations to form the gene family today of epsilon, gammaG gammaA, delta and beta

Question 5

Split genes

Answer 5

Genes with non coding (introns) and coding regions (exons). Give opportunity for evolution because introns are large and so there is better chance for recombination within and so reshuffling of exons. E.coli and yeast dont have this system so divide fast but lose major way of evolution

Question 6

Site specific recombination

Answer 6

chromosome of mobile genetic element added to the target chromsome. Can be scheduled as in bacteriophage where target and donor are cut with stick ends at regions of homology. Or can be more haphazard as with transposons where donor is blunt ends and target is sticky ends.

Question 7

Transposable elements

Answer 7

10% of our genome. 50% of all spontaneous mutation is them in drosophilia. can catalyse sequence changes once it is inserted into sequence. These may be incomplete excision, precise excision leaving duplicate target site, excision with extra target site inverted and excision with deletion. Transposons with similar IR could flank an exon and transposase may excise it because it recognises these repeats and reinsert it into another gene.

Question 8

Transposition in drosophilia

Answer 8

TE followed by local rearrangement disrupts white eye gene and leads to red/white eye mutants

Question 9

Transposition in antirrinhum

Answer 9

TE inserted disrupting pal gene and making two colours. Excision deletes 10 bases and adds four changing colour to mutant

Question 10

Maize transposition

Answer 10

discussed earlier. disrupts kernal colour

Question 11

Transposition burst

Answer 11

when all TE happen at once, usually they are quiescent. However under stress they all jump out ie drought. Maybe one seed will produce mutation that will allow it to survive