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BIOL1010/1011 > Evolution: Lecture 3 > Flashcards

Evolution: Lecture 3 Flashcards

1
Q

What is an allele?

A

An allele is an individual variant of a gene at some locus.

ex. R or r

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2
Q

What is a genotype?

A

A genotype is an individual’s combination of two alleles at a locus (for diploid species)

ex. Rr

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3
Q

What is a population?

A

A localized (typically geographically clustered) group of interbreeding and interacting species.

  • They are more likely to breed with their own population rather than those from other populations.
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4
Q

Each species is made up of?

A

One or more populations that can interbreed when they meet.

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5
Q

Populations evolve?

A

Populations are what evolve over generations, experiencing changes.

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6
Q

What is a gene pool?

A

The gene pool is the total genetic variability in populations, including all alleles at all gene loci in all individuals.

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7
Q

What are fixed alleles?

A

Fixed alleles occur when the whole population is homozygous at a locus for the same allele.

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8
Q

What are polymorphic loci?

A

When there are 2 or more alleles in a population, each being present in the population at some frequency.

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9
Q

Where are polymorphic loci found?

A

The standard sexual population contains mostly polymorphic loci.

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10
Q

How many polymorphic loci do most populations have?

A

Most populations have thousands of polymorphic loci.

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11
Q

Where do we see variation?

A

We see genetic variation at polymorphic loci, which is where natural selection comes in and acts on it.

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12
Q

Source of Genetic Variation?

A

New alleles arise by mutation in existing alleles. A single mutation can result in a new allele.

  • New allele creates variation
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13
Q

Mutations occurring in a particular environment?

A

Most mutations don’t meaningfully affect fitness - neutral variation in respect to natural selection (called neutral alleles)

Some reduce fitness: harmful alleles
(a.k.a. ‘deleterious’ mutations/alleles)

A very few increase fitness: beneficial alleles

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14
Q

Microevolution?

A

Microevolution is the change in the frequencies of alleles over generations

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15
Q

Extreme evolutionary change?

A

At the extreme, ‘change’ can mean the fixation of an allele, or the loss (extinction) of an allele.

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16
Q

Example of having 1 locus with 2 alleles?

A

Incomplete Dominance in a flower population.

Red: 320 RR
Pink: 160 RW
White: 20 WW

n = 500

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17
Q

Genotypic frequency?

A

Number of observed / total number

Ex. RR - 320/500 = 0.64

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18
Q

Allele frequencies?

A

Total R and r / total number times 2

Total R is number of homozygous individuals X 2 plus number of heterozygous individuals.

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19
Q

Allele frequencies: p and q?

A

p + q = 1
p is one allele frequency
q is the other allele’s frequency

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20
Q

p?

A

p = frequency of RR + frequency of RW/2

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21
Q

q?

A

q = frequency of WW + frequency of RW/2

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22
Q

H-W Principle uses?

A

Calculating genotype and phenotype frequencies and can be done by using census data of a population

23
Q

What is the Hardy-Weinberg Principle?

A

Describes expected relationships between allele and genotype frequencies in an idealized population when there is no evolution.

24
Q

When is H-W applicable?

A

Occurs under certain assumptions, including random mating.

25
Q

Model of random mating?

A

We can model random mating by taking two random alleles out of the population pool and sticking them together to create a combination of alleles.

26
Q

Hardy-Weinberg equation?

A

For two alleles, it is as follows:

p^2 + 2pq + q^2 = 1

  • p^2 and q^2 are the expected frequencies of the two homozygote genotypes
  • 2pq is the expected frequency of heterozygotes
27
Q

What does the Hardy-Weinberg equation let us do?

A

Lets us estimate the proportion of a population that are carrier of a recessive genetic disorder.

28
Q

Uses of the H-W principle?

A

We can estimate the allele and genotype frequencies. Example: finding the prevalence of carriers (heterozygotes) of recessive genetic disorders.

29
Q

Cystic Fibrosis - Allele and Genotype frequencies?

A

Cystic fibrosis is a single-locus recessive disorder, which affects 1 in 2500 people of European descent
(i.e. frequency is 1/2500 = 0.0004)

30
Q

What is the estimated frequency of
carriers (i.e. heterozygotes) in the European population? 1 in 2500 have the disorder, 0.0004.

A

q2 is frequency of disorder genotype = 0.0004
q (frequency of disorder allele) = √0.0004 = 0.02

p (frequency of normal allele) = 1 - q
p = 1 - 0.02 = 0.98

Frequency of heterozygote genotype = 2pq
= 2 x 0.98 x 0.02 = 0.0392
So an estimated ~4% (1 in 25) are carriers

31
Q

Other uses of Hardy-Weinberg principle?

A

Populations with genotype frequencies that conform to the equation are said to be in Hardy-Weinberg equilibrium at that locus.

We can look at population genotype frequencies to see if they are actually in Hardy-Weinberg equilibrium.

32
Q

Is this population in Hardy-Weinberg equilibrium?

1000 individuals:

400 RR
200 RW
400 WW

A

ACTUAL frequencies of genotypes:
{RR} = 400/1000 = 0.4
{RW} = 200/1000 = 0.2
{WW} = 400/1000 = 0.4

ACTUAL frequencies of alleles:
p = {RR} + {RW}/2 = 0.4 + 0.1 = 0.5 q = 1 - p = 0.5

Hardy-Weinberg equation: p2 + 2pq + q2 = 1

EXPECTED genotype frequencies (when p = 0.5 & q = 0.5):
{RR} = p2 = 0.52 = 0.25
{RW} = 2pq = 2 x 0.5 x 0.5 = 0.5
{WW} = q2 = 0.52 = 0.25

33
Q

What are the assumptions of the Hardy-Weinberg principle?

A

1) No net mutations
2) Random mating
3) No natural selection
4) Very large (infinite) population size
5) No migration

34
Q

What happens if there is a violation of one of these assumptions?

A

Violation of any of these assumptions usually signals evolutionary change.

35
Q

What are the three causes of microevolution?

A

Natural selection
Gene flow
Genetic drift

36
Q

Natural selection violates?

A

No natural selection

37
Q

Gene flow violates?

A

No migration

38
Q

Genetic drift violates?

A

Very large (infinite) population size

39
Q

Natural selection is the only?

A

Of these causes of microevolution, only natural selection results in adaptive evolution. That is, it is the only thing that causes greater suitability for the environment.

40
Q

What is gene flow?

A

Migration, where an individual moves from one population to another (population of the same species) or interbreeds with a member of another population.

41
Q

Gene flow is also?

A

Dispersal of gametes (e.g. pollen) or migration

  • Gene flow from population with different allele frequencies causes a change in allele frequencies, causing evolutionary change
  • Gene flow can introduce new alleles to a population
42
Q

Assumption: very large population?

A

Frequencies of alleles should not change if it is a large population.

43
Q

What is Random Genetic Drift?

A

A fluctuation from one generation to the next in the frequency of alleles within one population.

44
Q

Random Genetic Drift?

A

‘Sampling error’: random changes in allele frequencies over generations

  • Can lead to fixation (or extinction) of alleles in the population with the absence of natural selection
45
Q

Rate of drift depends on?

A

The rate of drift strongly depends on the size of the population. It can be ignored in very large populations but can be detected in smaller populations in just a few generations.

  • The time taken to have an allele go extinct or become fixed.
46
Q

Genetic drift is random:

A

A neutral allele at frequency 0.5 is equally likely to eventually be fixed or to go extinct, as it is equally far away from both.

[In theory, chance of eventual fixation of a neutral allele is the same as its frequency]

47
Q

What is a genetic bottleneck?

A

Breeding population is very small for a time
– Genetic drift powerful: allele frequencies change, many alleles fixed or go extinct.

48
Q

Genetic bottleneck diversity?

A

Lower genetic diversity overall, even if population later expands in numbers as it won’t recover well

49
Q

Can rare alleles frequencies change?

A

Some rare alleles can increase in frequency
= high frequencies of harmful alleles possible (even fixation of slightly harmful alleles)

50
Q

Founder effect in progress?

A

A few individuals found a new population from the ancestral population. A new population grows, and the gene pool of new population reflects the small sample of alleles present in the founders population.

51
Q

What is the founder effect?

A

Some previously rare alleles end up being much more common in the new population

e.g. High prevalence of particular genetic diseases in isolated human populations

52
Q

Greater Prairie Chickens of Illinois?

A

Went through a genetic bottleneck effect.

  • There was a lower genetic variability than larger populations
  • They had much reduced reproductive success: fitness lowered by accumulated harmful alleles.
53
Q

Endangered Populations/species?

A
  • Genetic diversity (gene pool) can be increased by adding individuals from other populations
  • Captive breeding programs manage matings to preserve remaining genetic diversity

BIOL1010/1011 (22 decks)

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