Chapter 23 - The Evolution of Populations

Question 1

What mechanisms can cause the evolution of populations?

Answer 1

Natural selection, genetic drift, and gene flow

Question 2

Natural selection acts on individuals, but only ______ evolve

Answer 2

…populations…

Question 3

Microevolution?

Answer 3

the change in allele frequencies in a population over generations
–evolution @ its smallest scale

Question 4

3 mechanisms cause allele frequency change (microevolution)

Answer 4

–Natural selection (adaptation to environment)
–Genetic drift (chance events alter allele frequencies)
–Gene flow (migration/transfer of alleles btwn populations)

Question 5

Genetic variation?

Answer 5

Variation in heritable traits (a prerequisite for evolution by natural selection)

Question 6

Phenotype?

Answer 6

the product of inherited genotype & environmental influences

Question 7

Genetic variation originates when…

Answer 7

…new genes and alleles arise by mutation, gene duplication, or other processes

Question 8

New alleles arise by…

Answer 8

…mutation/change in the nucleotide sequence of DNA

Question 9

Mutations can be caused by…

Answer 9

…replication errors/exposure to certain types of radiation/chemicals

Question 10

Sex reproduction can produce genetic variation by recombining existing alleles via:

Answer 10

1. Crossing over
2. Independent assortment
3. Fertilization (random gamete combos)

Question 11

Crossing over?

Answer 11

Exchange of genetic material btwn homologous/similar chromosomes during meiosis

Question 12

Independent assortment?

Answer 12

Random distribution of chromosomes into gametes during meiosis

Question 13

Example of beneficial heterozygote protection:

Answer 13

cystic fibrosis

Question 14

Point mutations in noncoding regions usually cause…

Answer 14

…neutral variation (no selective advantage/disadvantage)

Question 15

Mutation rates are ____ in animals & plants

Answer 15

…low…

Question 16

RNA viruses have _____ mutation rates & short generations bc their genes lack repair mechanisms

Answer 16

…high…

Question 17

A locus is fixed if everyone is…

Answer 17

homozygous for the same allele

Question 18

If there are two or more alleles for a locus, diploid individuals may be…

Answer 18

homo/heterozygous

Question 19

Genotype frequency is ____ as allele frequency

Answer 19

NOT THE SAME THING

Question 20

The sum of alleles is always…

Answer 20

1 (100%)

Question 21

Allele frequency formula

Answer 21

p + q = 1

Question 22

Hardy-Weinberg Equation (what does it do?)

Answer 22

describes the expected genetic makeup for a population that ISN’T evolving (if it equals 1) at a particular locus.

Question 23

Hardy-Weinberg Equation

Answer 23

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

Question 24

Conditions for Hardy-Weinberg Equilibrium

Answer 24

1. No mutations (no new genes allowed)
2. Random mating (equal opportunity)
3. No natural selection (no favoritism)
4. Extremely large population size (genetic drift happens if too small)
5. No gene flow (no new genes allowed)

Question 25

3 major factors that alter allele frequences directly & bring abt the most evolutional change:

Answer 25

natural selection, genetic drift, & gene flow

Question 26

Genetic drift tends to...

Answer 26

...reduce genetic variation thru random loss of alleles

Question 27

(genetic drift) Founder effect?

Answer 27

Few become isolated from larger population

Question 28

(genetic drift) Bottleneck effect?

Answer 28

Drastic reduction in population size due to sudden environmental change (ex: natural disaster)

Question 29

Genetic drift general:

Answer 29

--significant in small populations --can cause allele frequencies to change at random --can lead to loss of genetic variation in group --can cause harmful alleles to be fixed

Question 30

Gene flow?

Answer 30

Movement of alleles among populations & tends to reduce variation among populations over time --affects adaptation to local environments

Question 31

Only ________ consistently inc the freq of alleles that provide reproductive advantage

Answer 31

...natural selection...

Question 32

3 ways natural selection can alter the freq distribution of heritable traits:

Answer 32

--Directional selection --Disruptive selection --Stabilizing selection

Question 33

Directional selection?

Answer 33

Favors individuals at one extreme end of phenotypic range

Question 34

Disruptive selection?

Answer 34

Favors individuals at both extremes of the phenotypic range

Question 35

Stabilizing selection?

Answer 35

favors intermediate variants & acts against extreme phenotypes

Question 36

Sexual dimorphism?

Answer 36

A difference in secondary sexual characteristics btwn sexes (ex: men & women have different features)

Question 37

INTRAsexual selection?

Answer 37

Direct competition among individuals of one sex (usually males) for mates of opposite sex

Question 38

INTERsexual selection/mate choice?

Answer 38

Individuals of one sex (usually females) are choosy in selecting mates --Female choice usually dependent on showiness of male's appearance/behavior --"good genes" hypothesis: females select males w/ traits related to genetic quality/overall health

Question 39

Heterozygote advantage

Answer 39

occurs when heterozygotes have higher fitness/reproductive success than homozygotes