Natural Selection

Question 1

Gene flow

Answer 1

the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

Question 2

Sorting

Answer 2

beneficial alleles are favored by natural selection, whereas deleterious ones are removed

Question 3

Is natural selection random?

Answer 3

No

Question 4

adaptive evolution

Answer 4

species and populations evolve because natural selection consistently increases the frequencies of alleles that provide reproductive advantage
-occurs as the match between an organism and its environment increases

Question 5

Adaptations

Answer 5

traits that have evolved through the mechanism of natural selection

Question 6

What does natural selection increase the frequencies of?

Answer 6

alleles that enhance survival and reproduction

Question 7

Why is adaptive evolution a continuous process?

Answer 7

Because the environment can change

Question 8

What are the 3 modes of natural selection?

Answer 8

1. Directional
2. Disruptive
3. Stabilizing

Question 9

Directional selection

Answer 9

favors individuals at one end of the phenotypic range

Question 10

Disruptive selection

Answer 10

favors individuals at both extremes of the phenotypic range

Question 11

Stabilizing selection

Answer 11

favors intermediate variants and acts against extreme phenotypes

Question 12

How does directional selection change the average value of a trait?

Answer 12

Over time, directional selection 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
Example: 1977 drought, small seed to large seed environment, bird beaks increased in length

Question 13

How does disruptive selection increase variation in a trait?

Answer 13

Disruptive selection increases variation by favoring extreme phenotypic values, even if the mean of the distribution does not change
Ex: mandible width, wider mandibles can open tough shells of large seeds, slimmer mandibles are more adept at handling small seeds

Question 14

How does stabilizing selection reduce variation in a trait?

Answer 14

Stabilizing selection decreases variation and stabilizes the mean of a trait in a population around a particular, usually optimal, value
Ex: optimal gestational age is around 38-40 weeks

Question 15

Fitness

Answer 15

the contribution an individual makes to the gene pool of the next generation

Question 16

Relative fitness

Answer 16

The contribution of a genotype to the next generation, compared w/ contributions of alternative genotypes for the same locus

Question 17

Selection coefficient (s)

Answer 17

A measure of the relative intensity of selection against a given genotype (s = 1 - w)

Question 18

Heterozygote advantage (overdominance)

Answer 18

Heterozygote has greater fitness than either homozygote, results in a balanced polymorphism

Question 19

Heterozygote disadvantage (underdominance)

Answer 19

Heterozygote has lower fitness than either homozygote

Question 20

Peppered moth

Answer 20

-Industrial melanism
-Two morphs: typica (light, peppered, recessive) and carbonaria (dark, melanic, dominant)
-dramatic increases in frequency of carbonaria moth in polluted areas but not in non-polluted areas
-carbonaria form confers protection from bird predation in polluted areas
-As air pollution declines, typica form starts increasing in frequency again in once-polluted areas
-carbonaria form is now very rare across Britain
-strong differential bird predation against melanic peppered moths