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BIOL 121 > 23 Evolutionary Processes > Flashcards

23 Evolutionary Processes Flashcards

1
Q

Natural selection

A

individuals with certain phenotypes (heritable traits) survive better and produce more offspring than individuals with other phenotypes; certain alleles associated with favored phenotypes increase in frequency

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2
Q

Genetic variation

A

(1) the number and relative frequency of alleles present in a particular population (2) the proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences

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3
Q

What are the four modes or patterns of natural selection?

A

directional selection, stabilizing selection, disruptive selection, balancing selection

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4
Q

Directional selection

A

mode of natural selection that favours one extreme phenotype with the result that the average phenotype of a population changes in one direction; generally reduces overall genetic variation

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5
Q

What do you call alleles that reach a frequency of 1 and alleles that reach a frequency of 0?

A

fixed and list

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6
Q

Purifying selection

A

selection that lowers the frequency of or even eliminates deleterious/disadvantageous alleles

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7
Q

Stabilizing selection

A

a mode of natural selection that favors phenotypes near the middle of the range of phenotypic variation; reduces overall genetic variation but no change in average value of a trait over time

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8
Q

Disruptive selection

A

mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation; increases overall genetic variation

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9
Q

How can disruptive selection lead to speciation?

A

If mating only occurred between those with identical extreme phenotypes, selection would result in two distinct populations and may eventually form two new species

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9
Q

Speciation

A

the formation of new species

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10
Q

Balancing selection

A

mode of natural selection where no single allele is favored over time and across locations, on average; an overall balance in terms of fitness and frequency is maintained

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11
Q

When does balancing selection occur?

A

(1) heterozygote advantage (2) the environment of a population varies over time so the alleles favored by natural selection also varies (3) frequency-dependent selection

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12
Q

Heterozygote advantage

A

pattern of natural selection that favors heterozygous individuals (fitness advantage) compared with homozygotes; a form of balancing selection

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13
Q

Frequency-dependent selection

A

pattern of selection where certain alleles are favored when they are rare; a form of balancing selection

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14
Q

Most fundamental attribute of natural selection

A

it increases fitness and leads to adaption

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15
Q

Genetic drift

A

any change in allele frequencies due to chance (i.e. blind luck or sampling error); causes allele frequencies to drift up and down randomly over time and can eventually lead to fixation or loss

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16
Q

Small-scale definition of evolution

A

a change in allele frequencies at a genetic locus in a population from one generation to the next

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17
Q

Three key points about genetic drift

A

(1) random with respect to fitness (2) most pronounced in small populations (3) can lead to the random loss or fixation of alleles over time

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18
Q

What are the two special cases of genetic drift?

A

founder effects and bottlenecks

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19
Q

Founder effect

A

change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (the group is not a representative sample of the source population)

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20
Q

Founder event

A

when a group of individuals immigrate to a new geographic area and establishes a new population

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21
Q

Genetic bottleneck

A

reduction in the diversity of alleles in a population resulting from a sudden reduction in the size of that population (population bottleneck) due to a random event

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22
Q

Gene flow

A

the movement of alleles between populations; occurs when individuals leave one population, join another, and breed

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23
Q

What is the outcome of gene flow?

A

Gene flow homogenizes (or equalizes) allele frequencies between the source population and the recipient population

24
Q

What increases genetic diversity? Where do entirely new alleles come from?

A

Mutation

25
Q

What ways can mutation occur?

A

Point mutations, chromosome-level mutations, lateral gene transfer

26
Q

Deleterious allele

A

an allele that reduces an individual’s fitness and tends to be eliminated by purifying selection

27
Q

Beneficial allele

A

an allele that allows individuals to produce more offspring and should increase in frequency in the population due to natural selection

28
Q

Neutral allele

A

an allele with no effect on fitness, which occurs when a point mutation is silent

29
Q

What is mutation’s role in evolution?

A

(1) It is the ultimate source of genetic variation (2) If it didn’t occur, evolution would eventually stop (3) Mutation alone is usually inconsequential in changing allele frequencies in a particular gene

30
Q

What are the three forms of non-random mating?

A

inbreeding, assortative mating, and sexual selection

31
Q

Inbreeding

A

mating between closely related individuals; increases homozygosity of a population and often leads to a decline in the average fitness via selection (inbreeding depression)

32
Q

Two fundamental points about inbreeding

A

(1) Inbreeding increases homozygosity (2) Inbreeding only changes genotype frequencies, not allele frequencies, so it is not an evolutionary mechanism

33
Q

Inbreeding depression

A

decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in a population due to inbreeding; results from the exposure of deleterious recessive alleles to selection

34
Q

What are the two causes of inbreeding depression?

A

(1) Many recessive alleles represent loss-of-function mutations (2) Many genes, especially those involved in fighting disease, are under intense selection for heterozygote advantage, a selection process that favors genetic diversity

35
Q

Assortative mating

A

mating that is nonrandom with respect to specific traits

36
Q

Positive assortment

A

individuals choose mates that share a particular phenotypic trait with them; like mates with like

37
Q

Negative assortment or Disassortative mating

A

individuals choose mates that differ in a specific phenotypic trait; opposites mate

38
Q

Big-picture definition of evolution

A

all organisms on earth are related by common ancestry and they have changed over time and continue to change via the major evolutionary forces

39
Q

Population Genetics

A

combines genetics and evolutionary biology to make predictions/inferences about populations

40
Q

Population

A

a group of interbreeding individuals from the same species, living in the same place at the same time

41
Q

Gene Pool

A

pool of all possible genes and their alleles in a population

42
Q

What assumptions are we aking when predicting offspring genotype frequencies using the HWE model?

A

(1) random fusion of gametes or random mating so sex doesn’t matter with respect to the gene (3) a very large population so there is no change to allele frequency if someone doesn’t contribute (4) no other changes to allele frequencies between generation or no evolution

43
Q

How do we know if a population is changing over time?

A

HWE gives us a baseline or null model that describes the scenario where the population is not changing over time, meaning no evolution is occurring

44
Q

What are the assumptions of the HWE model that can be violated by evolutionary mechanisms?

A

(1) No new alleles are generated (2) Population is so large that if someone doesn’t reproduce, it doesn’t affect allele frequencies much (3) No genotype is more successful than the others at surviving and reproducing (4) No new alleles are added by new individuals coming into the population (5) Gametes combine at random in the gene pool to create the next generation

45
Q

How can you tell if a population is in HWE?

A

A population with observed genotype frequencies that have the same or very similar expected genotype frequencies

46
Q

Hardy-Weinberg Equilibrium

A

A mathematical null model describing genotype frequencies in a population that is not evolving, that is when all gametes go into a single group (gene pool) and combine at random to form offspring

47
Q

IF the observed genotype frequencies are different from the expected genotype frequencies, does this mean the population has evolved?

A

It MAY have evolved IF the allele frequencies also changed and that difference persists into the next generation. We can say that it is not in HWE, meaning one of the assumptions is not met.

48
Q

How can you tell if a population is NOT in HWE?

A

A population with a 50% or more difference between at least one genotype’s observed frequency and expected frequency.

49
Q

Mutations are unpredictable (random) with respect to…

A

an individual’s environment, effect on the individual’s phenotype, effect on the individual’s fitness

50
Q

Fitness

A

how successful an individual is at passing alleles to offspring relative to other members of its population i.e. lifetime reproductive success

51
Q

What is the impact of mutations?

A

can have a negative, positive, or neutral effect (but very rarely beneficial) and usually minor but it depends on the location and the environmental context

52
Q

How can you determine the size of the effect of a mutation?

A

generally, the more base pairs affected by mutation, the larger the effect, the more likely it will be harmful

53
Q

Prerequisites of natural selection

A

(1) the trait has to have variation (2) the trait is heritable at least in part (3) fitness has to vary because of the trait

54
Q

Sexual selection

A

non-random variation in reproductive success due to variation in mating and/or fertilization success; occurs when individuals within a population differ in their ability to attract mates and favors individuals with heritable traits that enhance their ability to obtain mates

55
Q

Asymmetry of sex

A

female fitness is not usually limited by ability to find a mate while male fitness is limited by the number of females they can mate with; features that increase male fitness may decrease fitness of some females, vice versa

56
Q

Fitness of an individual vs. a trait vs. an allele

A

Individual: the number of offspring she/he produces in a lifetime; Trait: the number of individuals in the next generation with that trait; Allele: the number of copies of that allele that successfully make it into the next generation

57
Q

Adaption

A

a heritable trait that is associated with higher fitness in the current environment; trait is heritable, has a function, and affects fitness

BIOL 121 (9 decks)

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