CHAPTER 23: Evolution

Question 1

what is microevolution?

Answer 1

change in allele frequencies in a population over generations evolution at smallest scale, there’s little to no change.

Question 2

what is natural selection?

Answer 2

adaptation to environment

Question 3

what is genetic drift?

Answer 3

chance events after allele frequencies

Question 4

what is gene flow?

Answer 4

transfer of alleles between populations

Question 5

what are 3 mechanisms that cause allele frequency change and bring the most evolutionary change?

Answer 5

natural selection, genetic drift, and gene flow

Question 6

what do genetic drift and gene flow have in common ?

Answer 6

they increase or decrease frequency of beneficial alleles in a population

Question 6

what is genetic variation ?

Answer 6

variation in heritable traits, a prerequisite for evolution by natural selection

Question 6

at the gene level, genetic variation quantified?

Answer 6

by percentage of heterozygous loci in a population

Question 6

how does genetic variation originate?

Answer 6

when new genes arise from mutation, gene duplication, or other processes.

Question 7

at the molecular level, how is genetic variation quantified?

Answer 7

by comparing the nucleotide sequences of two or more individuals

Question 7

how can sexual reproduction produce genetic variation?

Answer 7

by recombining existing alleles

Question 8

how do new alleles arise?

Answer 8

by mutation

Question 9

what is mutation?

Answer 9

a change in the nucleotide sequence of DNA

Question 10

how can mutations be caused?

Answer 10

by replication errors or exposure to certain types of radiation or chemicals

Question 11

what is heterozygote protection ?

Answer 11

it maintains a pool of alleles that could be beneficial if the environment changes

Question 11

what is neutral variation?

Answer 11

a non harmful mutation with no selective advantage or disadvantage.

Question 11

when does natural variation occur?

Answer 11

occurs within genes due to redundancy in the genetic code.

Question 11

what is a key, potential source of genetic variation?

Answer 11

duplication of small segments of DNA, including gametes.

Question 12

what are the 3 mechanisms where new combinations of existing alleles can occur?

Answer 12

crossing over, independent assortment, and fertilization?

Question 13

what is crossing over?

Answer 13

exchange of genetic material between homologous chromosomes during meiosis

Question 14

what is independent assortment ?

Answer 14

random distribution of chromosomes into gametes during meiosis

Question 15

what is fertilization?

Answer 15

random combination of gametes

Question 16

what is the gene pool?

Answer 16

consist of all copies of every allele at every locus in all members of the population

Question 16

how is a locus fixed in a population?

Answer 16

if all individuals in a population are homozygous for the same allele.

Question 17

what is adaptive evolution ?

Answer 17

a process in which traits that enhance survival or reproduction increase in frequency over time.

Question 18

how does genetic drift reduce genetic variation?

Answer 18

through the random loss of alleles, allele frequencies change randomly

Question 19

what is the founder effect ?

Answer 19

when few individuals become isolated from larger population

Question 20

what is the bottleneck effect?

Answer 20

when there is a drastic reduction in population size due to a sudden change in the environment

Question 21

what happens to the resulting population's gene pool after the bottleneck effect?

Answer 21

it may or may not longer be reflective of the original population's gene pool. (loose genetic variation)

Question 21

what does gene flow do to populations?

Answer 21

tends to reduce variation

Question 21

how can alleles move through gene flow?

Answer 21

through there movement of fertile individuals or gametes

Question 22

what are 2 important things gene flow can do?

Answer 22

1. increase a population's fitness 2. affect adaptation to local environments

Question 23

what is the only mechanism that consistently causes adaptive evolution? why?

Answer 23

natural selection, it involves both chance (new genetic variations) and sorting (beneficial alleles are sorted by natural selection)

Question 23

what are 3 ways natural selection can alter the frequency distribution of heritable traits?

Answer 23

directional selection, disruptive selection, and stabilizing selection?

Question 23

what is directional selection?

Answer 23

it favors individuals at one extreme end of phenotypic range

Question 24

what is disruptive selection?

Answer 24

favors individuals at both extremes of the phenotypic range

Question 24

what is stabilizing selection?

Answer 24

favors intermediate variants and acts agasint extreme phenotypes

Question 24

what is sexual selection?

Answer 24

process where individuals with certain heritable traits are more likely to obtain mates than other individuals of the same sex

Question 24

what is sexual dimorphism?

Answer 24

difference in secondary sexual characteristics between the sexes

Question 25

what does sexual selection result in?

Answer 25

sexual dimorphism

Question 26

what are the two types of sexual selection?

Answer 26

intersexual and intersexual?

Question 26

intrasexual selection? and an example

Answer 26

within a sex. males compete for females

Question 27

what is intersexual selection? and an example

Answer 27

between sexes. usually showy colors

Question 27

what is balance selection?

Answer 27

preserves variation at some loci by maintaining stable frequencies of 2 or more phenotypes

Question 27

what is the good genes hypothesis?

Answer 27

proposes that females select males with traits that are related to their genetic quality or overall health.

Question 28

what 2 things does balance selection include?

Answer 28

frequency-dependent selection and heterozygote advantage

Question 29

what is frequency-dependent selection?

Answer 29

where the fitness of a phenotype depends on how common it is

Question 29

what is the heterozygote advantage?

Answer 29

occurs when heterozygotes have a higher fitness than both kinds of homozygotes

Question 30

what are the 4 reasons why natural selection cannot fashion perfect organisms?

Answer 30

1. can only act on existing variations 2. evolution is limited by historical constraints 3. adaptations are often compromises 4. chance, natural selection, and the environment interact

Question 30

what does the sickle cell allele do?

Answer 30

affects the structure and function of hemoglobin, reducing the oxygen carrying capacity of red blood cells