15) Ploidy Flashcards

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1
Q

What is ploidy?

A

Some organisms have extra copies of some or all chromosomes

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2
Q

What is aneuploidy?

A

Some organic
Loss or gain of individual chromosomes or large chunks of them
Usually happens through chromosomal non-disjunction- Sister chromatids do not separate properly during Meiosis I or Meiosis II
Associated with developmental conditions

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3
Q

What are the different subdivisions of aneuploidy?

A

1) Monosomy= Loss of 1 individual chromosome e.g. Y chromosome or part of one chromosome
2) Trisonomy= Gain of one individual chromosome= Down’s syndrome
3) Tetrasomy, pentasomy and so on…gain of 2 or 3 etc individual chromosomes

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4
Q

Why are aneuploidies so damaging?

A

Humans in particular are very sensitive to genome loss= losses or gains of only 1-5% of genome can have hugely deleterious effects
Gene dosage: Gene expression is balanced across pair of homologous chromosomes= If chromosomes numbers aren’t quite right= Gene expression will be out of balance

Could be responsible for spontaneous abortions

Chromosomal disorders can be heritable= 5% of Down’s syndrome are inherited but 95% are spontaneous

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5
Q

What is polyploidy?

A

Organisms gain another copy of their entire genome (lots of chromosomes)
Whole genome is duplicated, common in plants

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6
Q

What is the problem with polyploidy?

A

Cannot get through meiosis- prophase I

Homologous chromosomes need to segregate correctly or gametes produced will not be viable

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7
Q

What is autopolyploidy?

A

Type of polyploidy where the multiple sets of genomes come from the same species or individual

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8
Q

What is the problem with autopolyploids?

A

Have too many homologous chromosomes= Instead of 2 chromosomes pairing up at meiosis, get multivalents= 3 chromosomes tripling up if they’re triploid etc..)

Creates jumble at spindle= Hard for cell to untangle and separate during meiosis

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9
Q

What is allopolyploidy?

A

Type of polyploidy where the extra genome comes from a different species

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10
Q

What is the problem with allopolyploidy?

A

Formation starts with 2 games from different species= Fuse –> forms hybrid zygote
Interspecific hybridisation happens in animals e.g. mules
BUT: Chromsomes form each parent aren’t similar enough to form homologous pairs at meiosis= Chromosome segregation into gametes end up being random

THEREFORE: Chances of getting a full set in any one gamete are pretty low
Can grow by mitosis but cannot produce gametes= Sterile

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11
Q

What can plants do to overcome the problem of allopolyploidy?

A

Somatic doubling
S-phse but without cell division afterwards= Hybrid tetraploid (2n x 2=4n) zygote
Now each chromosome has a homologue= Own copy produced during the somatic doubling= Zygote can grow up in a plant that can undergo meiosis= Produce gametes
Example: domestication of bread wheat
Incorrect mitosis where 2 chromosomes are replicated= can now find homologous chromosome

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12
Q

What are the advantages of polyploidy?

A

1) Allows genes to be brought in from closely related species through hybridisation= Broaden gene pool
2) Allows extremely rapid speciation (over course of one generation)= Allow plants to expand into other ecological niches
3) Gene expression is often related to amount of DNA in cell= Polyploid organisms can produce more gene product per cell= More productive e.g. wheat
4) More copies of a gene in cell= Allow some copies to change= raw material for evolution

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