Lecture 34 Flashcards Preview

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Flashcards in Lecture 34 Deck (21):
1

C-value (amount of DNA) paradox:

- The amount of DNA does not correlate with perceived complexity of position of the phylogenetic tree
- Complexity = number of ell types, metabolic complexity, behavioural complexity

2

What explained genome size variation?

- Gene duplication
- Satellites (often heterochromatic
- Relative rate of insertions and deletions
- Transposable elements
- Polyploidy (whole genome duplication)

3

Euploid:

- Having a complete complement of chromosomes

4

Aneuploid:

- Having an incomplete complement of chromosomes

5

Autopolyploidy:

- Whole genome is duplicated within a species
- (self duplication)
- Banana's, peanut, potato

6

Allopolyploidy:

- Genome duplication deriving from hybridisation between two parental species
- Eg) wheat, cotton, apples, sugar cane

7

The mechanics:

- Somatic doubling
- Polyspermy
- Gemetic non-reduction

8

Somatic doubling:

Mitotic double then failure of cell division

9

Polyspermy:

Multiple sperm fertilise the same egg

10

Gemetic non-reduction

- Failur of cell division during meiosis (2n gametes)
- Doesn't happen much in animals, but does in plants
- Can occur from sterile hybrids

11

How common is polyploidy?

- Very common in plants! (70% of angiosperms)
- 15% of speciation events in angiosperms
- Fairy common in fish (asexual reproduction), amphibians and insects
- Rare in mammals

12

What varieties and polyploidy:

- AA (einkorn) crossed with BB (goat grass)
- AABB (durum wheat, used for pasta) crossed with DD (goat grass)
- Bread wheat today is AABBDD
- Happened about half a million years ago

13

Red viscacha rat:

- 4N! it has double the amount of DNA of related species
- Genomic in situ hybridisation (label with fluorescent DNA and wash away, so only the fluorescent label is left where there is a good match)
- Showed that allopolyploidy is likely

14

What evidence is there for ancient polyploidy events?

- Evolutionary jumps in C-value
- Chromosome pairing patterns
- Gene number
- Gene arrangement
- Gene tree topology
- Age of gene duplication events (molecular clock)

15

Is yeast a peleo-polyploid?

- No evidence that duplicated gene blocks are duplicated again
- All blocks have the same centromere-telomere orientation (some should show an inversion if it were multiple-sub)
- Synonymous site divergence is about the same of all pairs of blocks (suggests duplication at the same time)

16

Vertebrate '2R' hypothesis:

- 2 rounds of poly-ploidy in the vertebrate lineage
- Based on evidence from C-value (amount of nuclear DNA), isozymes, and two pairs of duplicated genes on chromosome 11 and 12 delineating duplicated chromosomes
- This was confirmed

17

In order to determine if duplication events were close together using the molecular clock method we need:

- Enough species to cover before/after putative duplication events
- Enough genes to five statistical power
- Whole genomes are ideal

18

'2R' in the seed plants:

- Species tree for plants is well known, a gene tree is also well known
- There have been two whole genome duplication events, this was proved by comparing eudicots, monodictos and plotting them on a species tree

19

Possible selective advantages (some are also disadvantages) for polyploidy:

- Increased DNA content
- Increased heterozygosity (able to retain sufficient genet diversity even with small census size, potential for subfunctionalization and differential expression, higher mutation rate)

20

Possible costs of polyploidy:

- Chromosomal pairing errors and sex determination
- Developmental: orchestration of gene expression called a 'genomic shock', and timing of DNA replication, dosage compensation
- Physiological: higher DNA content requires more phosphorus
- Population: initially rare, loss due to drift. Competition with locally adapted progenitor species

21

How do benefits and costs compare evolutionarily?

- Recently formed polyploids have a higher extinction rate, lower speciation rates and lower diversification rates
- But polyploidy seems to be able to drive longer timer evolutionary success