Chapter 23

Question 1

Where do all new variations come from?

Answer 1

Mutations

Question 2

Can a mutation affect the genetic frequency of a whole population?

Answer 2

Not generally, no

Question 3

Gene flow

Answer 3

movement of genes from one population to another

Question 4

Immigration

Answer 4

members of a population move to a new location.

Question 5

Emigration

Answer 5

members of an established population leave

Question 6

What do both immigration and emigration cause?

Answer 6

Rapid and large scale changes to genetic frequencies

Question 7

Assortative Mating

Answer 7

a tendency of individuals to mate with phenotypically similar individuals

Question 8

What is the effect of Assortative mating?

Answer 8

frequency of homozygous individuals rise; less diversity in resulting population

Question 9

Dissassortive Mating

Answer 9

also called “outcrossing”, is a deliberate attempt to mate with phenotypically dissimilar individuals

Question 10

What is the effect of disassortative mating?

Answer 10

makes the frequency of heterozygote rise, and increases diversity

Question 11

Genetic Drift

Answer 11

All random events that can affect gene frequency in a SMALL POPULATION

Question 12

Bottleneck effect

Answer 12

makes a large population small by some random event wherein fitness did not help survival (randomly selected genes remaining)

Question 13

Founders Effect

Answer 13

Small group of pioneers (random selection), grows to large population that has the same genetic frequency as the founders

Question 14

Selection

Answer 14

the name given to the effect that environmental forces (resource availability, etc) have on WHICH members of a population survive

Question 15

Is selection random?

Answer 15

No, selection is SYSTEMIC (those who survive have the trait that will help them survive, and that trait is favored)

Question 16

Disruptive selection

Answer 16

Favors extremes (AA + aa)

Question 17

Directional Selection

Answer 17

Favors one extreme over another (Aa+ AA)

Question 18

Stabilizing selection

Answer 18

Favors heterozygote

Question 19

How does sickle cell anemia represent stabilizing selection?

Answer 19

One homozygote doesn’t show it, one homozygote kills the host, the hétérozygote that carries sickle cell benefits

Question 20

Why do variations persist?

Answer 20

The environment keeps changing; different traits are favored for different reasons

Question 21

What is the Hardy Weinberg assumption?

Answer 21

gene frequencies in a population will remain the same over time

Question 22

What are the conditions necessary for hardy-weinberg?

Answer 22

Populations must be large, random mating is occurring, no selection, no mutations, and no migration.

Question 23

What is the hardy-weinberg equation?

Answer 23

p^2 + 2pq + q^2 = 1

Question 24

If the recessive gene in it’s homozygous condition became lethal, what would happen to the frequency of p & q in four generations?

Answer 24

p increases, q decreases (but not to 0, because it can be carried and not expressed)

Question 25

If the dominant phenotype suddenly became fatal at birth, what would happen to the frequency of p and q in four generations?

Answer 25

decrease to p=0, increase to q = 1, since the gene can’t be carried without being expressed