CH23 II Flashcards

1
Q

What is the consequence of natural selection?

A

The favoring of some alleles over others causes adaptive evolution, organisms well adapted to their environment

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2
Q

What are the two forms of genetic drift?

A

Founder effect and bottleneck effect

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3
Q

Describe

Founder effect

A

Individuals become isolated indiscriminately from a large population and establish a new population with a different gene pool

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4
Q

Describe

Bottleneck effect

A

Sudden change in environment that drastically reduces population size. Low levels of genetic variation for generations are to be expected as a consequence.

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5
Q

What are some other characteristics of genetic drift?

A
  • It is most significant in small populations
  • It is unpredictable
  • Leads to loss of genetic variation
  • Can cause harmful alleles to become fixed
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6
Q

What does gene flow do, in terms of genetic variation?

A

It reduces genetic differences between populations, if not erase them. Can be good or bad.

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7
Q

Out of the mechanisms that alter allele frequencies the most, which one is responsible for adaptive evolution?

A

Natural selection. It is actually the only one that consistently causes adaptive evolution

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8
Q

Define

Relative fitness

A

The contribution an individual makes to the gene pool of the next generation relative to other individuals’ contribution

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9
Q

What does natural selection act on?

A

It acts on phenotype directly and indirectly, the genotype. This is why recessive traits are hard to select against.

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10
Q

Define

Absolute fitness

A

Number of offspring that inviduals with a certain trait have

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11
Q

What are the types of natural selection?

A

Directional, disruptive and stabilizing

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12
Q

Define

Directional selection

A

Conditions favor a phenotype extreme

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13
Q

Define

Disruptive selection

A

Conditions favor both phenotype extremes

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14
Q

Define

Stabilizing selection

A

Conditions act against both extremes; favors intermediates

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15
Q

Define

Sexual selection

A

Form of selection in which individuals with certain inherited characteristics are more likely to obtain mates

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16
Q

What does sexual selection lead to?

A

It leads to sexual dimorphism

17
Q

Define

Sexual dimorphism

A

Differences between the two sexes in secondary sexual characteristics (size, colour, ornamentation, behavior)

18
Q

What are the types of sexual selection?

A

Intrasexual selection and intersexual selection

19
Q

Define

Intrasexual selection

A

Competitions between one sex (usually males) for mates of the other sex

20
Q

Define

Intersexual selection

A

Individuals of one sex (usually females) are choosy in selecting their mates from the other sex (based on dimorphism).
ex: bright plumage makes a male more visible to predators but if it helps it reproduce, the pros outweigh the cons

21
Q

Define

Balancing selection

A

Type of selection that preserves at least two genes at a certain locus

22
Q

Describe

Heterozygote advantage

A

Individuals who are heterozygous at a particular locus have a greater fitness than both homozygotes. Could be a stabilizing, directional selection force, depending on genotype-phenotype relationship. Ex: heterozygotes for B polypeptide coding gene (sickle-cell anemia) are protected against malaria

23
Q

Describe

Frequency-dependent selection

A

The fitness of a given phenotype depends on how frequent or infrequent it is in the population

24
Q

Why is natural selection unable to create perfect organisms?

A
  1. New alleles cannot be created out of nothing, must be a variant of the fittest phenotype
  2. Complex structures (ex: wings) cannot be created out of nothing
  3. Adaptations are often compromises (humans have agility but little structural reinforcement)
  4. Chance events can affect the evolutionary course, what was “adapted” at one point might not be the next year