Lecture 14- Huge plant genomes and polyploidy Flashcards
what is chromosome reshaping
post-duplication, chromosomes can reorganise to form a larger single chromosome rather than the 2 separate ones
examples of how you can use information on WGD
can track divergence to this point- e.g. can identify ancestral states of eudicots and monocots through tracing back WGD events
what is another factor which can contribute to the expansion of plant genome sizes
retrotransposons and duplication of repeated sequences
type 1 vs 2 retrotransposons (basic mechanism)
type 1- copy-paste
type 2- cut-paste
names of some plant LTR retrotransposons
Ty1 and 3
monocots- estimate of how much genome can be made up of retrotransposons
65%
estimate of retrotransposon % in conifers
85%
relationship between genome size and repetitiveness
variable at small sizes, slight positive correlation, medium-sized genomes are often almost entirely repeats, at larger sizes, repetitive fraction starts to drop
tldr there is some correlation, but it gets a bit weird
auto- vs allopolyploidy
auto- multiple chromosome sets derived from a single taxon, no disjunction
allo- multiple chromosomes derived from multiple taxa
timelines of polyploidy- how long does fixation take/when do dead ends start to arrive
5-100my to fixation (roughly)
10my to extinction if the polyploidy is a dead end
example of polyploidy development
wheat- hybridisatiob between 2 diploids to form tetraploid, then tetra+diploid to produce hexaploid plants, very little reshaping in this case
diploidisation
loss of a chromosome through reorganisation
example of how population level changes can lead to changes in genome size
suppression of TEs due to selection can bring down genome size
less effective selection can lead to larger genomes, as more becomes fixed- e.g. smaller pops
