L11 Polyploidy Flashcards

1
Q

C value paradox

A

the amount of DNA does not correlate with perceived complexity on the phylogenetic tree

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2
Q

Complexity

A

number of cell types
metabolic complexity
behavioural complexity

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3
Q

The fraction that is coding vs Intergenic changes

A
  • for prokaryotes and viruses, about 10% of the genome is intergenic
  • for animals and plants, less than 10% may encode for proteins
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4
Q

What explains genome size variation?

A
  1. Gene duplication
  2. blocks of duplication
  3. satellites
  4. relative rate of insertions and deletions
  5. Transposable elements; 40% of human genome is TE
  6. Polyploidy
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5
Q

Polyploid

A

Having more than two complete sets of chromosomes e.g. 3n, 4n,5n

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6
Q

Euploid

A

Having a complete complement of chromosomes

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7
Q

Aneuploid

A

Having an incomplete complement of chromosomes e.g. missing/having an extra chromosome, trisomy 21

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8
Q

Autopolyploidy

A

Duplication of the genome with a species e.g. potato, banana

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9
Q

Allopolyploidy

A

Genome duplication deriving from hybridisation between two parental species e.g. wheat, cotton

The gametes are 2n

Distinct from a diploid hybrid

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10
Q

Somatic doubling

A

mitotic doubling then failure of cell division- vegetative propagation in plants

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11
Q

Polyspermy

A

multiple sperm fertilising an egg - 1-3% of human conceptions (not viable)

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12
Q

Gametic non-reduction

A

See OneNote diagram

failure of cell division during meiosis producing 2n gametes - unreduced sperm uncommon in animals, common step in pathway to allopolyploidy in plants

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13
Q

How common is polyploidy?

A
  • very common in plants, 70% lineages of angiosperms and led to 15% angiosperm speciation events
  • fairly common in fish, amphibians, insects
  • rare in mammals
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14
Q

Red Vischacha rat

A

See OneNote

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15
Q

Wheat varieties

A

See OneNote

  • hexaploid
  • homeologues
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16
Q

Homeologues

A

Homologs derived from polyploidization event

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17
Q

Diploidization

A
  • most loci now behaving/segregating like diploids
18
Q

What evidence is there for ancient polyploidy events?

A

See OneNote

  • paleo-polyploidy
    1. evolutionary jumps in c-value e.g. red verschacha rat
    2. evolutionary jumps in chromosome number
    3. Chromosomal pairing- quadrivalents?
    4. Gene number
    5. Gene arrangement
    6. Gene tree topology
    7. Age of gene duplication events (molecular clock)
19
Q

C-value

A

C-value is the amount, in picograms, of DNA contained within a haploid nucleus (e.g. a gamete) or one half the amount in a diploid somatic cell of a eukaryotic organism.

20
Q

Ancient genome duplication

A

See OneNote

- gene loss after duplication

21
Q

Multiple sub-genomic duplications

A

See OneNote

  • not whole genome duplication
  • more than 2 copies of some genes
22
Q

Yeast - a paleo-polyploid?

A

See OneNote

23
Q

Vertebrate 2R hypothesis

A

See OneNote

  • Susumu Ohno proposed that there had been two rounds of polyploidy in the vertebrate lineage
  • C-value
  • Isozymes
  • Identified two pairs of duplicated genes on chromosome 11 and 12 delineating duplicated chromosomal segment

Found consistent data in mice homeobox

24
Q

Evidence for 2R hypothesis

A

See OneNote

25
2R in seed plants?
See OneNote - point of divergence should match - 2 distinct peaks
26
Proximate causation
- mechanistic explanation e.g. failure of gamete reduction
27
Ultimate causation
- the why question
28
Possible selective advantages
1. increased DNA content 2. increased heterozygosity 3. able to retain genetic diversity even with small census size 4. multiple gene copies 5. higher mutation rate(could also be a cost)
29
Increased DNA content
See OneNote | 4 points
30
Increased heterozygosity
See OneNote | 2 points
31
Able to retain genetic diversity even with small census size
See OneNote | 2 points
32
Multiple gene copies
- neofunctionalisation | - sub-functionalisation
33
Possible costs
1. chromosomal 2. developmental 3. physiological 4. population
34
Chromosomal costs
See OneNote | 2 points
35
Developmental costs
See OneNote | 3 points
36
Physiological costs
See OneNote | 1 point
37
Population costs
See OneNote | 3 points
38
Correlated with asexual reproduction
- in plants asexual reproduction may be a consequence of self-incompatibility systems breaking down - polyploid insects and reptiles probably arose from parthenogenic animals
39
Parthenogenesis
reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants.
40
Asexual reproduction
Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes
41
Reconciling costs and benefits
``` Recently formed polyploids have: 1. higher extinction rate than diploids 2. lower speciation rate 3. lower diversification rate YET polyploidy appears associated with major evolutionary diversification events ```