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B3.0 > Genetic Mechanisms Of Morphological Change > Flashcards

Genetic Mechanisms Of Morphological Change Flashcards

1
Q

Genetic mechanisms of morphological change

A

Finding the mutations that matter

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2
Q

Key qs under genetic mechanisms of morphological change

A

1) how important are “gene duplication” mutations
2) where in genes do key mutations occur? Exon vs cis-reg
3) reproducibility? Does convergent evolution use the same mutations?
4) can we track a pathway of mutations?

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3
Q

Do extra genes facilitate evolution?

A
  • TG and WGD
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4
Q

TD

A
  • v.Common
  • 2v similar genes near each other in genome (pair wrongly @ meiosis)
  • crossover in/near gene generated gametes w/ 3 copies/ 1 copy
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5
Q

TD: can start from one gene

A
  • If there are TEs nearby
  • 1 gene becomes 2/0
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6
Q

WGD

A
  • evidence is in genome sequences
  • e.g. human C13
  • e.g. pufferfish C6&7
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7
Q

2R

A
  • at the base of the vertebrates
  • v. Important for structure of human genome
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8
Q

3R

A

At the base of the teleost fish

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9
Q

4R

A

In a few !

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10
Q

Seed plants

A

Ancestral polyploidy events

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11
Q

Possible consequences of gene duplication (can confound phylogenies)

A
  1. Nonfunctionalisation
  2. Subfunctionalisation
  3. Neofunctionalisation
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12
Q

Ortholog

A

Same gene, different sp.

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13
Q

Paralog

A

Different gene by duplication

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14
Q

Ortholog v paralog

A

Not always easy to work out due to
- gene loss
- gene conversion

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15
Q

Exon

A

Altered protein function

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16
Q

Cis-regulatory change

A

Altered time/place of expression

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17
Q

Methodology

A

1) breeding expts (aka trait mapping)
2) wild pops
3) domesticated sp.

18
Q

Sliding Hox gene expression

A
  • cis-regulatory elements near Hox clusters?
  • changes to an upstream TF
19
Q

Breeding experiments (aka trait mapping)

A
  • need a breedable species w/ variation
  • find a DNA variant inherited precisely w/ trait of interest
  • co-segregation
20
Q

Three-spiked sticklebacks (Gasterosteus aculeatus)

A
  • ancestrally marine
  • invaded freshwater when ice sheets retracted
  • each pop evolved adaptations to the new habitat
  • e.g. smaller spines
21
Q

F1 gen

A

Boring! Virtually all the same

22
Q

F2 gen

A

= 100s
- Some spiny, some not
- genotype by PCR/SNP arrays/sequencing
- co-inheritance of polymorphism and phenotype

23
Q

Small spines map to

A

the tip to of chromosome 7, next to Pitx1

24
Q

Pitx1 in 3-spine sticklebacks

A
  • known limb/fin developmental gene
  • coding sequence = identical
  • expression pattern = different
  • deletion removed enhancer region (independent across pops)
  • KO mice: smaller; asymmetrical: left leg not reduced as much (bias)
  • KO in fish: asymmetrical fins
25
Q

Pitx2

A
  • partially compensates Pitx1 KO
  • left expressed (R gene)
26
Q

Nine spined stickleback (Pungitius)

A
  • different Genus
  • also evolved some pops lacking pelvic spine
  • also moved into freshwater occasionally
  • is it the same gene?
27
Q

Three x nine-spine stickleback interspecific cross

A
  • mutations do not complement each other
  • infertile hybrid has no spiky fin
  • probably same locus
  • not a perfect test
28
Q

Manatees

A
  • mammals
  • Pelvic retention more L than R
29
Q

Investigating manatee F1 hybrids

A
  • comparing gene expt soon
  • cis-regulatory behaviour is parental
  • trans-regulatory (TFs), alleles change behaviour and cosegregate
30
Q

Protein annotation of manatees

A
  • compare many genomes for marine/freshwater
  • sequence
  • find correlating alleles
  • 17%: aa change
  • 41% regulatory (+42%?)
31
Q

Snowshoe hares

A
  • northern USA and Canada turn white @ winter moult photo period threshold; “winter white”
  • West coast; “winter brown”
  • phenotype spreading!
32
Q

Snowshoe hares

A
  • northern USA and Canada turn white @ winter moult photo period threshold; “winter white”
  • West coast; “winter brown”
  • phenotype spreading!
33
Q

Scan snowshoe hare genome

A
  • DNA variants close to Agouti gene co-segregate with unknown “winter brown” gene; likely to be Agouti allele
  • cis-reg change
  • jackrabbit origin
  • rare interbreeding
34
Q

Domesticated species

A

Look different due to artificial selection, but have v similar DNA

35
Q

Twin-tailed goldfish

A
  • 1000AD: domestication
  • 1596: 1st twin-tail phenotype
36
Q

Is there any zebrafish mutation causing

A

Tail twinning?
- yes, lethal!
- chordin: dorsal Bmp-antagonist in early embryo
- v. important

37
Q

Candidate gene approach (no trait mapping):

A
  • chordin: mutated in goldfish
  • clone and sequence chordin from lots of goldfish strain
38
Q

Candidate gene approach H

A
  • 2 copies (ChordinA, ChordinB)
  • 1 mutation: twin-tail
  • 2 mutations: lethal
39
Q

How to prove candidate gene approach H?

A

1) cross different genotypes in lab: perfect correlation!
2) rescue (inject -/- eggs w Chordin A); twin-tail

40
Q

Goldfish pathway

A

1) duplication
2) subfunctionalisation (cis-reg)
3) mutation

B3.0 (23 decks)

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