Lecture 1- Genome evolution Flashcards
4 examples of genomic changes
chromosome fusion
segmental duplications
inversions
translocations
example of a group where chromosome fusion has occured
within muntjacks- gone from 7+sex chromosomes to 4, with x included in the 1st by fusion at the tails
example of sex chromosomes becoming ‘chained’
in platypuses- pairing of sex chromosomes with autosomes
possible explanation for the existence of the Y chromosome
combination of non-recombining regions- can be seen as the Y chromosome seems to get smaller across evolutionary time as non-recombining regions can’t effectively be involved in evolution
common patterns in gene loss
fairly rapid loss, then stabilisation is a common pattern
can sometimes see a reason for the gene loss- e.g. loss of vit C biosynthesis when bird diets got enough of it, tooth genes lost in turtles etc when they stopped being needed
example of magnitude of gene loss
177 genes lost between 2 Drosophila species- shows gene loss within a genus
5 ways genes can emerge
-exon shuffling
-gene duplication with divergence
-retrotransposition
-gene fusion and fission
-de novo origination, development of a coding region from a non-coding region
other process where exon shuffling is often important
protein evolution- allows shuffling of domains
how can alternative splicing create new function?
new splice form, is useful, selection pressure
skipping exons, alternative exon exclusion, alternative promoters, and alternative polyA signals can all lead to new splices
introns early theory
introns were an ancient invention, and have been gradually lost since ~RNA world
introns late
introns evolved in early eukaryoyes, and kept spreading
introns very late is also an idea, suggests they emerged approx LECA
why is it hard to know when introns emerged?
theyre very variable within modern organisms
2R hypothesis
suggests there was a whole genome duplication event in vertebrates- possibly 2- but this still seems to happen a lot more in angiosperms than animals
example of subfunctionalisation
colour vision- X duplication led to the development of an M-gene from the duplicated L gene, allowing better colour vision, which has a selective advantage in primates
C-value paradox
genome size lacks correlation with gene number in eukaryotes, and ‘complexity’ doesnt seem to be important either- obvs hard to measure though
