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Biology 2 > Ch 23 The Evolution of Populations > Flashcards

Ch 23 The Evolution of Populations Flashcards

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1
Q

What is microevolution?

A

A change in allele frequencies in a population over generations.

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2
Q

Q: What are the three mechanisms that cause allele frequency change?

A

Natural selection
Genetic drift
Gene flow

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3
Q

Q: Which mechanism causes adaptive evolution?

A

A: Only natural selection.

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4
Q

Q: What does genetic variation refer to?

A

A: Changes in an organism’s genetic composition.

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5
Q

Q: What are discrete characters? Examples.
How is it determines?

A

Traits classified on an either-or basis. (Flower color)
Determined by a single locus with different alleles that produce distinct phenotypes

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6
Q

What are quantitative characters?

A

Traits that vary along a continuum within a population (e.g., plant height),
Usually due to polygenic inheritance

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7
Q

What is gene variability? How is it measured?

A

The variation of whole genes in a population, measured via Average Heterozygosity

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8
Q

Average Heterozygosity

A

the average percent of loci that are heterozygous

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9
Q

What is nucleotide variability?

A

Variation based on DNA sequence comparisons between two individuals, averaged across the population.

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10
Q

True/false: Gene variability exceeds nucleotide variability.

A

True

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11
Q

What is geographic variation?

A

Genetic differences between populations in different locations.

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12
Q

What is a cline?

A

A graded change in a trait along a geographic axis.

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13
Q

What causes the formation of new alleles?

A

Mutations in the nucleotide sequence of an organism’s DNA.

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14
Q

What mutations can be passed to offspring?

A

Only mutations in gametes.

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15
Q

What is a point mutation? Is it harmful?

A

A mutation that alters a single nucleotide, usually harmless but sometimes significant.

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16
Q

What are chromosomal mutations? Is it harmful?

A

Mutations that delete or rearrange many gene loci, often harmful.

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17
Q

What is gene duplication? What makes it an important source of?

A

duplicated gene segments persist and may develop new functions over time.
An important source of genetic variation

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18
Q

Why is gene duplication beneficial?

A

played a major role in evolutionary increase in gene number and diversity.

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19
Q

What is the average mutation rate per gene per generation in plants and animals?

A

About 1 mutation per 100,000 genes.

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20
Q

Why do prokaryotes accumulate mutations faster?

A

Due to their shorter generation times, even though their mutation rate is lower (10⁻¹¹ mutations per base pair per generation).

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21
Q

How do viruses generate rapid genetic variation?

A

Their short generation spans and higher mutation rates.

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22
Q

How does sexual reproduction contribute to genetic variation?

A

By producing unique combinations of alleles.

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23
Q

What are the three mechanisms of genetic shuffling in sexual reproduction?

A
  1. Crossing Over
  2. Independent Assortment of Chromosomes
  3. Fertilization
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24
Q

Why is genetic shuffling important for evolution?

A

It rearranges existing alleles into new combinations, providing the genetic variation necessary for evolution.

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25
What is a population in genetics?
A group of organisms of the same species in a given area that breed with one another.
26
What is a gene pool?
A common group of genes shared by the members of a population.
27
If only one allele exists at a locus. Is the the allele fixed? Will all individuals be homozygous?
Yes, yes
28
What happens to the individuals if 2 or more alleles exist?
individuals can be homozygous or heterozygous.
29
What is gene frequency (proportion)?
The number of times an allele appears in a population compared with other alleles of the same gene.
30
What is a species in genetics?
A group of similar-looking organisms that breed with one another and produce fertile offspring in the natural environment.
31
What does the Hardy-Weinberg Equation represent?
It describes a gene pool in evolutionary stasis, providing a baseline for genetic stability.
32
What are the two equations of Hardy-Weinberg?
p^2 + 2pq + q^6 = 1 𝑝 + 𝑞 = 1
33
What do the variables 𝑝 and 𝑞 represent?
𝑝: Frequency of the dominant allele 𝑞: Frequency of the recessive allele
34
What are the five conditions for Hardy-Weinberg equilibrium?
1. No mutations 2. Random mating 3. No natural selection (all genotypes have equal survival and reproductive success) 4. Extremely large population size 5. No gene flow (no migration in or out)
35
What does the Hardy-Weinberg theorem describe?
A non-evolving population where allele and genotype proportions remain constant.
36
Why is the Hardy-Weinberg theorem important?
1. It serves as a baseline for measuring evolutionary changes. 2. Provides a reference point for comparing allele frequencies across populations.
37
How does sexual reproduction affect genetic makeup in Hardy-Weinberg populations? (2 things)
1. Segregation and recombination of alleles during meiosis and fertilization do not alter the overall genetic composition. 2. With random mating, gene frequencies remain constant each generation.
38
What does the Hardy-Weinberg equation allow us to calculate?
Allelic frequencies in a gene pool if genotype frequencies are known.
39
What happens when a population is not in equilibrium?
1 or more evolutionary changes are occuring: Mutation (rare, with a small contribution to evolutionary change). Nonrandom mating (affects genotype frequencies, though changes are usually small).
40
What are the three main mechanisms that directly alter allele frequencies?
Natural Selection Genetic Drift Gene Flow
41
What is natural selection based on?
Differential reproductive success, where environmental conditions determine which individuals produce the most offspring.
42
What are the three conditions for natural selection to occur?
1. Variation must exist among individuals in a population. 2. Variation must result in differences in the number of offspring surviving. 3. Variation must be genetically inherited.
43
How does natural selection affect allele frequencies?
Individuals better suited to the environment pass on their alleles at different frequencies, changing the genetic makeup of the population.
44
What are examples of natural selection?
1. Selection to avoid predators. 2. Selection to match climatic conditions. 3. Selection for pesticide resistance.
45
What is genetic drift?
A sudden change in a population’s gene frequencies due to random events.
46
How does genetic drift differ between small and large populations?
Small populations: Gene frequencies change significantly from one generation to another due to sampling errors. Large populations: Genetic drift has a minimal effect, but specific situations can still alter allele frequencies.
47
What are the two main situations where genetic drift occurs?
1. Founder Effect: Rare alleles or combinations of alleles become enhanced when a few individuals are isolated from the original population. 2. Bottleneck Effect: A mass event reduces a population to a small number of individuals, which then repopulate (important in conservation biology for endangered species).
48
What are the four key points about genetic drift?
1. Significant in small populations. 2. Causes random changes in allele frequencies. 3. Leads to a loss of allelic variation. 4. Can cause harmful alleles to become fixed.
49
What is gene flow?
The transfer of alleles among populations due to the migration of fertile individuals or gametes.
50
Why is gene flow a powerful agent of change?
1. It homogenizes allele frequencies between populations. 2. It allows beneficial alleles to spread across populations. 3. It introduces new alleles, similar to mutation.
51
How does natural selection interact with gene flow?
Once gene flow introduces a new allele: Natural selection can increase its frequency (e.g., insecticide-resistance alleles in mosquitoes). Or decrease its frequency (e.g., copper-tolerance alleles in bent grass).
52
What is the only mechanism that consistently causes adaptive evolution?
Natural selection
53
What is relative fitness?
The contribution an individual makes to the gene pool of the next generation, relative to others.
54
What value is given to the most fit individuals?
A value of 1.
55
What factors combine to determine fitness?
1. Survival: How long the organism lives. 2. Mating success: How often it mates. 3. Number of offspring per mating that survive.
56
What are the three modes of selection?
Directional Selection Disruptive Selection Stabilizing Selection
57
What is directional selection? When is it common?
Favors one extreme of a trait. Common during environmental changes or migration to new habitats.
58
What is disruptive selection? When does it occur?
Favors both extremes of a trait. Occurs when intermediate phenotypes are less favored.
59
What is stabilizing selection?
Reduces phenotypic extremes. Favors intermediate variants.
60
How does natural selection drive adaptive evolution?
By increasing the frequency of alleles that enhance survival and reproduction, improving the match between species and environment.
61
Why is adaptive evolution a continuous process?
Because the environment changes, and natural selection adjusts to these changes over time
62
What is sexual selection?
individuals with certain traits are more likely to obtain mates
63
What is sexual dimorphism?
Differences in size, color, ornamentation, or behavior between sexes.
64
What are the two types of sexual selection?
Intrasexual Selection Intersexual Selection (Mate Choice)
65
Intrasexual selction
Competition within the same sex for mates. Example: Male-male competition or female dominance in ring-tailed lemurs.
66
Intersexual Selection (Mate Choice)
Individuals of one sex (usually females) select mates based on specific traits. Example: Showy plumage in male birds to attract females.
67
Why might female mate preferences evolve?
To select mates with traits indicating good health or strong genetic qualities, increasing offspring fitness.
68
What is neutral variation?
Differences in DNA that do not confer a selective advantage or disadvantage.
69
What 2 mechanisms preserve genetic variation?
Diploidy Balancing Selection
70
Diploidy
Recessive alleles are hidden in heterozygotes, allowing them to persist.
71
Balancing Selection
Maintains stable frequencies of multiple phenotypes.
72
What are the two types of balancing selection?
Heterozygote Advantage Frequency-Dependent Selection
73
Heterozygote Advantage
Heterozygotes have greater fitness than homozygotes. Example: Sickle-cell trait and malaria resistance.
74
Frequency-Dependent Selection:
Fitness of a phenotype depends on its frequency. Negative: Rare phenotypes are favored. Positive: Common phenotypes are favored.
75
What is oscillating selection?
Selection favors different phenotypes at different times, depending on environmental conditions.
76
Why can’t natural selection create perfect organisms?
1. Acts only on existing variations. 2. Evolution is constrained by history. 3. Adaptations are compromises. 4. Chance, natural selection, and the environment interact.

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