Chapter 21: Evolution

Question 1

define evolution

Answer 1

any change in allele frequency, genotype frequency, OR both constitutes evolution

Question 2

how do new alleles appear?

Answer 2

ONLY through mutation –> mutation makes new genes

Question 3

what does gene recombination do?

Answer 3

shuffles mutations to produce new sequences

Question 4

define locus

Answer 4

location of a gene on a chromosome

Question 5

what is the formula to find allele frequency?

Answer 5

(# copies of an allele) / (total # of alleles in a population)

Question 6

what drives evolution?

Answer 6

natural selection

Question 7

what drives natural selection?

Answer 7

genetic variation

Question 8

define species

Answer 8

individuals that can exchange genetic material through interbreeding

Question 9

define gene pool

Answer 9

all of the alleles present in all individuals of a single species

Question 10

define population

Answer 10

interbreeding group of organisms of the same species living in the same geographical area

Question 11

what are the two sources of genetic variation?

Answer 11

mutation and recombination (in both cases, new alleles are formed)

Question 12

define mutation

Answer 12

generates NEW variations in genes (new alleles)

Question 13

define recombination

Answer 13

shuffles gene mutations to make new combinations of mutations

Question 14

what are the two places where mutations occur?

Answer 14

somatic (occur in body tissues)

germ-line (occur in reproductive cells and are passed on)

Question 15

what are the 3 types of mutations?

Answer 15

deleterious
neutral
advantageous

Question 16

define “adapted”

Answer 16

better able to survive and reproduce in a particular environment

Question 17

define allele frequency

Answer 17

rtes of occurrence of alleles in populations

Question 18

what does it mean when a population is “fixed” for an allele?

Answer 18

when a population only exhibits one allele at a particular gene (no other genetic option besides that one allele)

when allele frequency is 1

Question 19

what are 3 ways we can measure genotype and allele frequencies in populations?

Answer 19

observable traits
gel electrophoresis
DNA sequencing

Question 20

define phenotype

Answer 20

observable traits

-a product of the genotype and the environment

Question 21

define Hardy-Weinberg equilibrium

Answer 21

the situation in which evolution does not occur

Question 22

what are the requirements for the Hardy-Weinberg equilibrium? (5)

Answer 22

1. everyone has same chance of surviving/reproducing
2. no migration, must be a closed society
3. no mutations
4. must be a large enough population to avoid sampling errors
5. individuals must mate at random (no sexual preferences)

Question 23

define non-random mating

Answer 23

when individuals do not mate at random

• sexual preferences
• affects genotype frequencies, but not allele frequencies

Question 24

what are the results of natural selection?

Answer 24

increases the frequency of beneficial alleles, resulting in adaptation

change in allele frequencies from generation to generation according to the allele’s impact on survival/reproduction of the individuals that hold that allele

Question 25

define competitive advantage

Answer 25

a function of how well an organism is adapted to its environment

Question 26

what does it mean if an organism is more “fit”? define fitness

Answer 26

a measure of the extent to which an individual’s genotype is represented in the next generation
(more fit, able to reproduce and survive and pass on genotype to offspring)

Question 27

define a “discrete” trait

Answer 27

a trait that is either/or

(ex. yellow or green) no in between

Question 28

define a “continuous” trait

Answer 28

a variation that occurs across a spectrum

ex. height

Question 29

define positive selection

Answer 29

when natural selection increases the frequency of a beneficial allele

Question 30

define negative selection

Answer 30

when natural selection decreases the frequency of a deleterious allele

Question 31

define balancing selection

Answer 31

when natural selection acts to maintain two or more alleles in a population at intermediate frequencies

Question 32

heterozygote advantage

Answer 32

describes the case in which the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype.

(ex. people in Africa who carry one allele for sickle cell and one that is vulnerable to malaria. they do not develop the deadly sickle cell disease, but they are less likely to get malaria because they are heterozygous for that blood type)

Question 33

define stabilizing selection

Answer 33

selects against extremes in a population

Question 34

define directional selection

Answer 34

selects against one of two extremes in a population

Question 35

define disruptive selection

Answer 35

selects against the mean in a population (results in extremes)

Question 36

define artificial selection

Answer 36

a form of directional selection

-successful genotypes are carefully manipulated and reproduced by a breeder

Question 37

define sexual selection

Answer 37

promotes traits that increase an individual’s access to reproductive opportunities

Question 38

define migration

Answer 38

movement of individuals from one population to another, resulting in gene flow

Question 39

define gene flow

Answer 39

the movement of alleles from one population to another

Question 40

define genetic drift

Answer 40

the random change in allele frequencies from generation to generation

• leads to evolution
• does NOT lead to adaptation
• impact depends on population size

Question 41

what is a population “bottleneck”

Answer 41

when a population falls to just a few individuals

Question 42

define a “founder event”

Answer 42

when just a few individuals arrive to colonize an island and begin a new population (type of bottleneck)

Question 43

define “molecular clock”

Answer 43

the correlation between the time two species have been evolutionarily separated and the amount of genetic divergence between them

Question 44

define “pseudogene”

Answer 44

a gene that is no longer functional