Lecture 8 'Unraveling the genomic basis of speciation'

Question 1

What is a species?

Answer 1

Same species can interbreed
Their offspring can reproduce
However, this definition is not applicable to all organism. An exception are bacteria.
Hybrids are baby’s of two different species which are not fertal.

Question 2

Reproductive isolation = Barrier + Evolutionary processes

Answer 2

Barrier:
- Allopatric speciation (geographical barrier)
- Sympatric speciation: Prezygotic barriers (day/night-habbitat isolation) & postzygotic barriers (infertility, physical limitations)
Evolutionary processes:
- Natrual selection
- Sexual selection
- Gene flow
- Change in population size
- Mutation

–> Isolation by itself is not a mechaism for evolutionary changes in species

Question 3

Hotspot paradox

Answer 3

The “hotspot paradox” predicts that recombination hotspots will be rapidly eliminated from populations in situations where there are strong cis-acting sequence determinants of hotspot activity
the directionality of the DSB repair process suggests that recombination hotspots should self-destruct, yet
recombination levels remain constant.

Question 4

two major things to produce healthy offspring

Answer 4

Meiosis and homologous recombination

Question 5

What underlies rapid hotspot turnover?

Answer 5

PRDM9 genes, they have a KRAB domain, SSXRD domain, PR/SET domain and a zinc finger domain. Regulation place of hotspot for recombination is regulated by the gene PRDM9.
The zinc finger domain in the PRDM9 is highly polymorphic, diversity in array size and in the identity. The diversity of PRDM9’s ZNF-array could solve the hotspot paradox.

Question 6

Role of PRDM9 in DSB repair

Answer 6

PRDM9 determines meiotic DSB localization, it binds on a place in the genome where it recognize the sequence, it opens the chromatin and it recruits the DSB machinery.

Question 7

Role of PRDM9 in speciation

Answer 7

Heterozygosity of PRDM9 as a cause of genetic incompatibility, PRDM9’s ZNF variation leads to hybrid sterility. Heterozygosity results in asymmetric binding of PRDM9.

Question 8

why is the hypothesis that KRAB-ZNFs are involved in hotspot regulation?

Answer 8

Because TE are a source of genomic instability. and they are ticking a lot of boxes on the recombination hotspot wish list:
- Hotspots must be common and widely dispersed across the genome
- hotspots must avoid genes
- Hotspots cannot have a function that is essential for cell viability