CH23 II

Question 1

What is the consequence of natural selection?

Answer 1

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

Question 2

What are the two forms of genetic drift?

Answer 2

Founder effect and bottleneck effect

Question 3

Describe

Founder effect

Answer 3

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

Question 4

Describe

Bottleneck effect

Answer 4

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

Question 5

What are some other characteristics of genetic drift?

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Define

Relative fitness

Answer 8

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

Question 9

What does natural selection act on?

Answer 9

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

Question 10

Define

Absolute fitness

Answer 10

Number of offspring that inviduals with a certain trait have

Question 11

What are the types of natural selection?

Answer 11

Directional, disruptive and stabilizing

Question 12

Define

Directional selection

Answer 12

Conditions favor a phenotype extreme

Question 13

Define

Disruptive selection

Answer 13

Conditions favor both phenotype extremes

Question 14

Define

Stabilizing selection

Answer 14

Conditions act against both extremes; favors intermediates

Question 15

Define

Sexual selection

Answer 15

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

Question 16

What does sexual selection lead to?

Answer 16

It leads to sexual dimorphism

Question 17

Define

Sexual dimorphism

Answer 17

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

Question 18

What are the types of sexual selection?

Answer 18

Intrasexual selection and intersexual selection

Question 19

Define

Intrasexual selection

Answer 19

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

Question 20

Define

Intersexual selection

Answer 20

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

Question 21

Define

Balancing selection

Answer 21

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

Question 22

Describe

Heterozygote advantage

Answer 22

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

Question 23

Describe

Frequency-dependent selection

Answer 23

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

Question 24

Why is natural selection unable to create perfect organisms?

Answer 24

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