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Evolutionary Genetics and Genomics > Lecture 34 > Flashcards

Lecture 34 Flashcards

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Biology 101 flashcards
1
Q

C-value (amount of DNA) paradox:

A
  • 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
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2
Q

What explained genome size variation?

A
  • Gene duplication
  • Satellites (often heterochromatic
  • Relative rate of insertions and deletions
  • Transposable elements
  • Polyploidy (whole genome duplication)
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3
Q

Euploid:

A
  • Having a complete complement of chromosomes
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4
Q

Aneuploid:

A
  • Having an incomplete complement of chromosomes
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5
Q

Autopolyploidy:

A
  • Whole genome is duplicated within a species
  • (self duplication)
  • Banana’s, peanut, potato
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6
Q

Allopolyploidy:

A
  • Genome duplication deriving from hybridisation between two parental species
  • Eg) wheat, cotton, apples, sugar cane
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7
Q

The mechanics:

A
  • Somatic doubling
  • Polyspermy
  • Gemetic non-reduction
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8
Q

Somatic doubling:

A

Mitotic double then failure of cell division

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9
Q

Polyspermy:

A

Multiple sperm fertilise the same egg

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10
Q

Gemetic non-reduction

A
  • Failur of cell division during meiosis (2n gametes)
  • Doesn’t happen much in animals, but does in plants
  • Can occur from sterile hybrids
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11
Q

How common is polyploidy?

A
  • 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
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12
Q

What varieties and polyploidy:

A
  • 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
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13
Q

Red viscacha rat:

A
  • 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
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14
Q

What evidence is there for ancient polyploidy events?

A
  • Evolutionary jumps in C-value
  • Chromosome pairing patterns
  • Gene number
  • Gene arrangement
  • Gene tree topology
  • Age of gene duplication events (molecular clock)
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15
Q

Is yeast a peleo-polyploid?

A
  • 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)
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16
Q

Vertebrate ‘2R’ hypothesis:

A
  • 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
Q

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

A
  • Enough species to cover before/after putative duplication events
  • Enough genes to five statistical power
  • Whole genomes are ideal
18
Q

‘2R’ in the seed plants:

A
  • 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
Q

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

A
  • 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
Q

Possible costs of polyploidy:

A
  • 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
Q

How do benefits and costs compare evolutionarily?

A
  • 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

Evolutionary Genetics and Genomics (34 decks)

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