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Molecular Genetics And Evolution > Week 4 > Flashcards

Week 4 Flashcards

1
Q

What is a population?

A

group of organisms of the same species living in the same geographical area

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2
Q

What is population genetics?

A

application of genetic principles to entire populations of organisms

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3
Q

What is an allele?

A

One of the alternative forms (different nucleotides) of a gene.

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4
Q

When we talk about alleles in population genetics, what are we mostly concerned with?

A

the frequencies of alleles in a population.

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5
Q

What do allele frequencies measure?

A
  • how common an allele is in a population
  • they can be calculated for each allele in a gene pool.
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6
Q

Where is genetic variation stored?

A
  • in a population’s gene pool.
  • made up of alleles and allele combinations form when organisms have offspring
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7
Q

What does genetic variation lead to?

A
  • Phenotypic variation
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8
Q

What is phenotypic variation necessary for?

A
  • natural selection.
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9
Q

What is the basis of evolution?

A
  • Changes in allele frequencies within or between populations
  • selection, mutation, genetic drift, gene flow
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10
Q

What are the four main processes that cause changes in allele frequencies (genetic variation)?

A
  • selection, mutation, genetic drift, gene flow.
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11
Q

What is the proximate mechanism for evolution?

A
  • allele frequency changes
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12
Q

What are the four main components of natural selection?

A
  • inheritance ( traits controlled by genes)
  • variation (genetic variation between individuals)
  • survival of the fittest (not all individuals mate)
  • differential survival and reproduction
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13
Q

What does natural selection occur in response to?

A
  • environmental pressures
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14
Q

Individuals do not evolve, ________ do

A
  • populations do.
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15
Q

What is evolution measured as?

A
  • change in relative proportions of heritable variations in a population over several generations.
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16
Q

Why is genetic variation important for evolution?

A
  • genetic variation leads to phenotypic variation, which is required for natural selection.
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17
Q

What does natural selection cause happen in a population?

A
  • different environmental pressures between populations so:
  • greater between-population genetic variation but
  • lower within-population genetic variation.
  • sometimes resulting in new species.
18
Q

What is a mutation?

A
  • a random change in the nucleotides of a gene.
19
Q

What is the ultimate source of genetic variation? How?

A
  • mutation
  • it increases genetic variation when it creates new alleles
20
Q

What are the types of mutation?

A
  • point mutations
21
Q

What are point mutations? When can it change a phenotype?

A
  • single base pair change in genome
  • in a coding region
22
Q

How can a point mutation be passed to offspring?

A
  • if it happens during gamete mutation it can be passed on to offspring
23
Q

What is genetic drift?

A
  • a change in allele frequencies caused by random sampling of alleles over generations.
  • completely random sampling.
  • some individuals not surviving randomly and loss of alleles.
  • random fluctuations
24
Q

Where does genetic drift act more quickly?

A
  • smaller populations
  • can reduce variation in these populations through the loss of alleles.
25
Q

What is fixation?

A
  • in genetic drift where an allele becomes the only allele because all others have been removed.
26
Q

Where does genetic drift usually happen?

A
  • founder effects (as well as bottlenecks)
  • reduced genetic variation from original population
  • a different sample of the genes in the original population.
27
Q

What is gene flow? When does this occur?

A
  • the transfer of alleles from one population to another
  • when individuals join new populations AND REPRODUCE
28
Q

What does high gene flow do?

A
  • keeps neighbouring populations similar and can maintain genetic variation within populations
29
Q

What does low gene flow do?

A
  • increases the chance that two populations will evolve into two different species and can lead to lower within-population genetic variation through inbreeding.
30
Q

If an individual is inbred:

A
  • has low heterozygosity
31
Q

If high heterozygosity?

A
  • high genetic variation.
32
Q

Genetic drift and low gene flow over time produce a march towards

A
  • homozygosity
33
Q

What is the Hardy-Weinberg equilibrium model? What does it explain?

A
  • a framework for understanding how populations evolve.
  • explains how Mendelian segregation influences allelic and genotypic frequencies in a population
34
Q

What does HWE describe? What are the 5 assumptions of hardy weinberg equilibrium?

A
  • populations that are not evolving
    1. no natural selection
    2. No mutation
    3. No migration (gene flow)
    4. Infinitely large population (to avoid genetic drift)
      Mating is random
35
Q

What does the HWE predict? What can we then do with those?

A
  • genotype frequencies in a population
  • compare those with actual frequencies from populations
  • used with simple mendelian inheritance (two alleles)
36
Q

Describe HWE equation:

A

p + q = 1
Then p2 + 2pq + q2 = 1

37
Q

If HWE assumptions are met, population will be in________

A
  • genetic equilibrium AKA hardy-weinberg equilibrium
38
Q

What are the two predictions of HWE?

A
  • allele frequencies do not change over generations
  • after on generation of random mating, genotypic frequencies will remain in the following proportions:
39
Q

How do you do HWE with two numbers (allele counts)?

A
  • first assign alleles
  • prepare a punnet square of allele combinations
  • we calculate the frequency of q2 because we know their alelle frequencies (both recessive - we don’t know this about p). Q2 = 12/(988+12) = 0.012
  • calculate the frequency of q of the recessive blue allele (y) so q = 0.11
  • we can minus that off 1 so p = 0.89
  • then apply the formula to get the genotype frequencies.
40
Q

Why do we use HWE?

A
  • it’s a good null hypothesis compared to values from a real population to describe statistically significant deviations from the equilibrium. If different, evolution is occuring
  • therefore either selection, mutation, or gene flow, or genetic drift is occuring to alter them.
  • these are occurring and violating the HW assumptions and constitutes a null model and is fundamental to the study of evolution.
41
Q
A

Molecular Genetics And Evolution (20 decks)

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