Microevolution III (Natural Selection)

Question 1

What does sorting mean in the context of natural selection?

Answer 1

Beneficial alleles are favored by natural selection, whereas deleterious ones are removed.

Question 2

Why is natural selection not random?

Answer 2

Natural selection consistently increases the frequencies of alleles that provide reproductive advantage, leading to adaptive evolution.

Question 3

What are adaptations?

Answer 3

Traits that have evolved through the mechanism of natural selection.

Question 4

When does adaptive evolution occur?

Answer 4

Adaptive evolution occurs as the match between an organism and its environment increases.

Question 5

Why is adaptive evolution a continuous process?

Answer 5

The environment can change, thus changing the traits that are favorable.

Question 6

What is the relationship between selection, phenotypes, and genotypes?

Answer 6

Selection “sees” and “favors” specific phenotypes, which results in changes of the frequencies of their corresponding genotypes.

Question 7

What is directional selection?

Answer 7

Natural selection that favors individuals at one end of the phenotypic range.

Question 8

What is disruptive selection?

Answer 8

Selection that favors individuals at both extremes of the phenotypic range.

Question 9

What is stabilizing selection?

Answer 9

Selection that favors intermediate variants and acts against extreme phenotypes.

Question 10

Over time, what change does directional selection cause?

Answer 10

It causes a change in the mean value of a character in a population that is either higher or lower than its current mean value, resulting in a shift in the plot of trait frequency.

Question 11

Over time, what change does disruptive selection cause?

Answer 11

Disruptive selection increases variation by favoring extreme phenotypic values, even if the mean of the distribution does not change.

Question 12

Over time, what change does stabilizing selection cause?

Answer 12

Stabilizing selection decreases variation and stabilizes the mean of a trait in population around a particular, usually optimal, value.

Question 13

What is fitness?

Answer 13

Fitness is the contribution an individual makes to the gene pool of the next generation.

Question 14

What is relative fitness?

Answer 14

Relative fitness is the contribution of a genotype to the next generation, compared with contributions of alternative genotypes for the same locus. The relative fitness W of the most fit genotype in a population is, by definition, W = 1.

Question 15

What is the selection coefficient (s)?

Answer 15

A measure of the relative intensity of selection against a given genotype. s = 1 - W

Question 16

What is W for the most fit genotype?

Answer 16

1.

Question 17

What is heterozygote advantage (overdominance)?

Answer 17

This occurs when the heterozygote has greater fitness than either homozygote, resulting in a balanced polymorphism.

Question 18

What is heterozygote disadvantage (underdominance)?

Answer 18

This occurs when the heterozygote has lower fitness than either homozygote.

Question 19

What preserves genetic variation in populations?

Answer 19

Much of the variation observed in natural populations is due to the combined action of mutation and genetic drift–definitely true for most variation at the level of the genotype and for some of the variation at the level of the phenotype.

Question 20

How does diploidy maintain genetic variation?

Answer 20

Diploidy maintains genetic variation in the form of recessive alleles hidden from selection in heterozygotes.

Question 21

What is sexual selection?

Answer 21

Natural selection for mating success, which often results in sexual dimorphism.

Question 22

What is sexual dimorphism?

Answer 22

Marked differences between the sexes in secondary sexual characteristics.

Question 23

What is intrasexual selection?

Answer 23

Direct competition among individuals of one sex (often males) for mates of the opposite sex.

Question 24

What is intersexual selection?

Answer 24

Often called mate choice, this occurs when individuals of one sex (usually females) are choosy in selecting their mates.

Question 25

What are the consequences of male showiness due to mate choice?

Answer 25

Male showiness can increase a male’s chance of attracting a female, but it can also decrease his chances of survival.

Question 26

What is the “good genes” hypothesis?

Answer 26

This hypothesis suggests that if a trait is related to male genetic quality or health, both the male trait and female preference for that trait should increase in frequency.