Lecture 27

Question 1

Define fitness

Answer 1

Relative reproductive success of a genotype compared to other genotypes in the population; fitness ranges from 0-1

Question 2

How do you calculate fitness?

Answer 2

Take the average number of offspring produced by a genotype and divide it by the mean number of offspring produced by the most prolific genotype

Question 3

Define the selection coefficient and how to calculate it

Answer 3

Relative intensity of selection against a genotype; selection coefficient = 1-fitness for a particular genotype

Question 4

Define directional selection

Answer 4

Selection in which one allele or trait is favored over another

Question 5

Define overdominance (heterozygote advantage)

Answer 5

Heterozygotes are favored over homozygotes and have a reproductive advantage which maintains both alleles in the population

Question 6

Define underdominance (heterozygote disadvantage)

Answer 6

Heterozygotes have a lower fitness than both homozygotes, which leads to an unstable equilibrium

Question 7

What effect does mutations have on allelic frequencies in the short and long-term?

Answer 7

Short: change in allelic frequencies

Long: equilibrium reached between forward and reverse mutations

Question 8

What effect does migration have on allelic frequencies in the short and long-term?

Answer 8

Short: change in allelic frequencies

Long: equilibrium reached when allelic frequencies of source and recipient population are equal

Question 9

What effect does genetic drift have on allelic frequencies in the short and long-term?

Answer 9

Short: change in allelic frequencies

Long: fixation of one allele

Question 10

What effect does natural selection have on allelic frequencies in the short and long-term?

Answer 10

Short: change in allelic frequencies

Long: directional selection; fixation of one allele; overdominant selection = equilibrium reached
underdominant selection = unstable equilibrium

Question 11

Define evolution

Answer 11

Genetic change in a group of organisms (change in gene frequency in a population over time)

Question 12

What is the concept of a phylogenetic tree?

Answer 12

Graphical representation of the evolutionary relationships among a group of organisms

Question 13

Describe the molecular clock and rates of evolution

Answer 13

Molecular clock: rate at which a protein evolves is roughly constant over time; therefore, the amount of change that a protein has undergone can be used as a clock

Question 14

What is the biological species concept?

Answer 14

Group of organisms whose members are capable of interbreeding with one another but are reproductively isolated from the members of other species; Ernst Mayr, 1942

Question 15

Define anagenesis and cladogenesis evolution

Answer 15

Anagenesis: evolution taking place in a single group (lineage) with the passage of time

Cladogenesis: splitting of one lineage into two; new species arise

Question 16

What is the neutral-mutation hypothesis?

Answer 16

Individuals with different molecular variants have equal fitness at realistic population size

Question 17

What is the balance hypothesis?

Answer 17

Genetic variation in natural populations is maintained by selection that favors variation

Question 18

Which statement is true of the neutral-mutation hypothesis?

a. All proteins are functionless
b. Natural selection plays no role in evolution
c. Most molecular variants are functionally equivalent
d. All of the above

Answer 18

C. Most molecular variants are functionally equivalent

Question 19

What are the prezygotic reproductive isolating mechanisms?

Answer 19

Ecological, behavioral, temporal, mechanical, gametic

Question 20

What are the postzygotic reproductive isolating mechanisms?

Answer 20

Hybrid invalidity, hybrid sterility, hybrid breakdown

Question 21

Define disruptive selection

Answer 21

Extremes (homozygous AA;aa) are favored

Question 22

Define stabilizing selection

Answer 22

Increase in the number of heterozygotes, compared to normal distribution, in a population because they have an advantage