L21 Genetic Conflict

Question 1

A gene’s eye view of evolution

Answer 1

we can think of alleles as competing for a spot in the genome - alleles that make good zebras become more common

Question 2

Meiotic drive

Answer 2

see onenote

• aka “segregation distortion”

Question 3

Evolution of a meiotic drive that causes death 33% of the time

Answer 3

see onenote

the driver spread despite reducing fitness by 33%

Question 4

Meiotic drive makes sense from the gene’s eye view of evolution

Answer 4

see onenote

sacrifice some between-individual fitness but gain some within-individual fitness

“intra-genomic conflict”

Question 5

Famous meiotic drive genes

Answer 5

see onenote

• the gene “Segregation distorter (SD)” exists in natural populations of Drosophila melanogaster
• located on Chr 2
• essentially a poison gene linked to a resistance gene

In SD/WT males, SD-bearing sperm develop normally and WT sperm do not

Question 6

Meiotic drive relies on (and selects for) reduced recombination

Answer 6

see onenote

some of the most common (successful_ variants of the SD chromosome have picked up inversions - inverted regions generally do not recombine

Question 7

Famous meiotic drive genes 2

Answer 7

• meiotic driver “Sex ratio”
• on the X chromosome
• males carrying Sex Ratio produce 100% X bearing sperm and only produce daughters
• could wipe out entire species by eliminating males

Question 8

Gene conversion

Answer 8

• similar to meiotic drive
• driver breaks the other allele, which is then repaired using the driver as a template
• in heterozygotes, the driver deletes the other allele and replaces it with a copy of itself

Question 9

Synthetic gene drive systems created in the lab using CRISPR-Cas9

Answer 9

see onenote

Question 10

Sometime TEs are useful (part 1)

Answer 10

• silk protein Fibroin evolved via repeated duplication of repetitive DNA by a transposable element

Question 11

Sometime TEs are useful (part 2)

Answer 11

neuronal protein Arc is evolutionarily related to retrotrasponson Gag protein and forms virus-like capsid structures that can transfer mRNA between cells in the nervous system

Question 12

Adaptations against TEs

Answer 12

• RNAi

- P elements

Question 13

RNAi

Answer 13

• use dicer in a eukaryote cell
• used by scientists to knock-down gene expression

Dicer

• Helps control retrotransposition
• Dicer recognises dsRNA (tends to be found in virus) chops it up, memorises that specific sequence => when nucleus produces that mRNA, dicer chops it up and prevents the production of that protein

Question 14

P-elements

Answer 14

• maternal RNA silences the transposon

- wild females have evolved RNAi - they load their eggs with RNA that stops the transposon from replicating

Question 15

P-elements, an example of a co-evolutionary arms race

Answer 15

see onenote

Question 16

TEs - relatives of viruses?

Answer 16

• retroviruses

- the “escape hypothesis”

Question 17

“Tame” viruses living in parasitic wasp genomes

Answer 17

• many wasps have “polyDNA” viruses encoded in their genome
• virus can pop out and infect a caterpillar on request
• virus might have originated from wasp DNA (it has introns)
• alternatively, it might be a retrovirus that moved in and became a symbiont (it has similar DNA sequences to certain “wild” viruses)