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1

how does natural selection act on individuals

each individual's combination of traits affects its survival and reproductive success compared to other individuals

2

____ are selected; ____ evolve

individuals; populations

3

microevolution

evolutionary change on its smallest scale; change in the genetic makeup of a population from generation to generation

4

darwin didn't have a satisfactory explanation for

how the heritable variations required for natural selection appear in populations or how organisms transmit these variations to their offspring

5

model proposed by gregor mendel

particular hypothesis of inheritance

stated that parents pass on discrete heritable units that retain their identities in offspring

6

darwin considered the raw material for natural selection to be

"quantitative" characters -- those characteristics in a population that vary along a continuum

7

mendel and other early geneticists worked only with

discrete "either-or" traits

8

geneticists later determined that

quantitative characters are influenced by multiple genetic loci and that the alleles at each of these loci follow Mendelian patterns of inheritance

9

population genetics

the study of how populations change genetically over time

10

population genetics gave rise to ____

modern synthesis

11

modern synthesis

a comprehensive theory of evolution that integrated ideas from many other fields

12

population

a localized group of individuals that are capable of interbreeding and producing fertile offspring

13

populations of the same species may be isolated from one another, thus exchanging genetic material only rarely. such isolation is common for populations

confined to different,. widely separated islands or lakes

14

individuals near the population center are more likely to breed with

members of their own population than other populations and thus on average are more closely related to one another than to members of other populations

15

gene pool

the aggregate of genes in a population at any one time

16

the gene pool consists of

all alleles at all gene loci in all individuals of the population

17

if only one allele exists at a particular locus in a population,

that allele is said to be FIXED in the gene pool, and all individuals are homozygous for that allele

18

if there are 2 or more alleles for a particular locus in a population,

individuals may be either homozygous or heterozygous

19

when there are 2 alleles at a particular locus, the convention is to

use p to represent the frequency of one allele and q to represent the frequency of the other allele

20

at loci that have more than 2 alleles,

the sum of all allele frequencies must still equal 1

21

hardy-weinberg theorem was derived in the year

1908

22

the hardy-weinberg theorem describes

the properties of gene pools that aren't evolving

23

the hardy-weinberg theorem states that

the frequencies of alleles and genotypes in a population's gene pool remain constant from generation to generation, provided that only mendelian segregation and recombination of alleles are at work

24

the hardy-weinberg theorem describes how

mendelian inheritance preserves genetic variation from one generation to the next in populations that aren't evolving

25

the hardy-weinberg theorem lays the groundwork for

undeerstading long-term evolutionary changes that darwin, lacking knowledge of genetics, couldn't have envisioned

26

the preservation of genetic variation provides the opportunity for

natural selection to act over many generations

27

the allele frequencies in all the gametes produced by the population

will be the same as in the original population

28

if the individuals in a population _______ and _______, this population will ______ and ________

donate gametes to the next generation at random and also mate at random;

have the same allele frequencies from one generation to the next, and its genotype frequencies can be predicted from the allele frequencies

29

a population's allele and genotype frequencies would remain constant if

a population were in hardy-weinberg equilibrium and its members continued to mate randomly generation after generation

30

a population ________ for its allele frequencies to remain constant

doesn't need to be in hardy-weinberg equilibrium

31

raw material of evolutionary change

genetic variation

32

conditions for hardy-weinberg equilibirum

1. extremely large population size
2. no gene flow
3. no mutations
4. random mating
5. no natural selection

33

genetic drift

chance fluctuations in allele frequencies from one generation to the next

34

the smaller the population, the greater

the role played by genetic drift

35

gene flow

transfer of alleles between populations; genetic additions to and/or subtractions from a population resulting from the movement of fertile individuals or gametes

36

gene flow can

alter allele frequencies

37

why do mutations modify the gene pool?

b/c they introduce or remove genes from chromosomes or change one allele into another

38

if individuals preferentially choose mates with certain genotypes,

random mixing of gametes doesn't occur

39

departure from the conditions for H-W equil. usually results in

evolution

40

while natural populations rarely if ever are in true H-W equil., in many populations

the rate of evolutionary change is so slow that these populations appear to be close to equilibrium

41

the hardy-weinberg equation can be used to

estimate the percentage of the population carrying the allele for an inherited disease

42

PKU

phenylketonuria, a metabolic disorder that results from homozygosity for a recessive allele. left untreated, it results in mental retardation and other problems

43

to use the H-W equation, we must assume that

we must also neglect

people don't choose their mates on the basis of whether or not they carry this a and don't generally mate w/ close relatives

any effects of gene flow from other populations, and differential survival and reproductive success among genotypes

44

which 2 processes produce the variation in gene pools that contributes to individual differences?

mutation and sexual recombination

45

____ and ____ originate only by mutations

new genes and new alleles

46

mutations

changes in the nucleotide sequence of DNA

47

most mutations occur in

somatic cells and are lost when the individual dies

48

only mutations in __________ can be passed to offspring, and _______

cell lines that produce gametes,

only a small fraction of these spread through populations

49

point mutation

change of one base in a gene

50

most point mutations are

probably harmless

51

why are most point mutations harmless?

much of the DNA in eukaryotic genomes doesn't code for protein products.

and because the genetic code is redundant, even point mutations in genes that code for protein may have little effect because they don't alter the protein's amino acid composition

52

changes in what type of DNA regions can have profound effects?

noncoding regions of DNA that regulate the expression of genes

53

what type of chromosomal mutations are almost certain to be harmful?

however, when such mutations ______, their effects on organisms may be neutral

chromosomal mutations that delete, disrupt, or rearrange many loci at once

leave genes intact

54

duplications of chromosome segments are

nearly always harmful

55

smaller pieces of DNA are often introduced into a genome through

the activity of transposable elements

56

if a duplicated segment doesn't have severe effects, it

can persist over generations, providing an expanded genome with new loci that may take on new functions by further mutations and subsequent selection

57

exons

coding portions of genes

58

new genes may also arise when

exons are shuffled within the genome

59

______ appear to have played a major role in evolution

beneficial increases in gene number

60

mutation rates

tend to be low in animals and plants, averaging about one mutation in every 100,000 per generation

61

mutations can rapidly generate genetic variation in

microorganisms and viruses with short generation spans

62

HIV has a generation span of

about 2 days

63

an RNA genome has

a much higher mutation rate than a typical DNA genome

64

in sexually reproducing populations, ____ is far more important than _____ on a generation-to-generation time scale in producing the variations that make adaptation possible

sexual recombination; mutation

65

nearly all phenotypic variations based on genetic differences result fro m

recombinational shuffling of the existing alleles in the gene pool

66

bacteria and many viruses can also undergo recombination, but

they do so less regularly than animals and plants and often in ways that allow them to cross species barriers

67

the ability of pathogens to ______, combined with their _______, makes them especially dangerous adversaries

evolve rapidly through extensive recombination; high mutation rates

68

although new mutations can modify allele frrequencies,

the change from one generation to the next is likely to be small

69

what does recombination do?

it reshuffles alleles but doesn't change their frequencies

70

effect of nonrandom mating

it can affect relative frequencies of homozygous and heterozygous genotypes but by itself usually has no effect on allele frequencies

71

the 3 major factors that alter allele frequencies annd cause most evolutionary change are

natural selection, genetic drift, and gene flow

72

result of natural selection in terms of alleles?

selection results in alleles being passed to the next generation in proportions different from their relative frequgencies in the present generation

73

over time, genetic drift tends to

reduce genetic variation through losses of alleles from the gene pool

74

2 situations that can increase the likelihood that genetic drift will have a large impact on a population are referred to as

the bottleneck effect and the founder effect

75

bottleneck effect

a sudden change in the environment (fire/flood) may drastically reduce population size. in effect, the survivors have passed thru a restrictive "bottleneck" and their gene pool may no longer be reflective of the original popoulation's gene pool

76

genetic drift may continue to have substantial effects on the gene pool for many generations until

the population is large enough that chance fluctuations have less effect

77

founder effect

when a few individuals become isolated from a larger population, this smaller group my establish a new population whose gene pool isn't reflective of the source population. these founders represent a distinct gene pool w/ different allele frequencies from those of the parent population

78

gene flow tends to

reduce differernces between populations

79

discrete characters often are determined by

a single gene locus with different alleles that produce distinct phenotypes

80

most heritable variation consists of

quantitative characters

81

heritable quantitative variation results from

the influence of 2 or more genes on a single phenotypic character

82

morphs

different forms that result when individuals differ in a discrete character

83

phenotypic polymorphism

a population is said to display phenotypic polymorphism for a character if two or more distinct morphs are each represented in high enough frequencies to be readily noticeable

84

genotypic polymorphism

the existence of 2 or more distinct alleles at a given locus in a population's gene pool

85

population geneticists measure the number of polymorphisms in a population by

determining the amount of heterozygosity at both the level of whole genes (gene variability) and the molecular level of DNA (nucleotide variability)

86

average heterozygosity

measured as the average percent of the loci in the genome that are heterozygous

87

nucleoitde variability is measured by

comparing the nucleotide sequences of DNA samples from 2 individuals and then averaging the data from many such comparisons

88

why does average heterozygosity tend to be greater than nucleotide variability

a gene can consist of thousands of bases of DNA. a difference at only one of these bases is sufficient to make 2 alleles of that gene dififerent and increase average heterozygosity

89

based on measurements of nucleotide variability, humans have

relatively little genetic variation compared to most species. 2 humans differ by only about 0.1% of their bases

90

geogrphic variation

differences between the gene pools of separate populations or population subgroups

91

most species exhibit _____ variation

geographic

92

cline

a graded change in a trait along a geographic axis

93

in some cases, a cline may represent

in other cases,

a graaded region of overlap where individuals or neighboring populations are interbreeding.

a gradation in some environmental variable may prorudce a cline

94

experimental studies of clines have confirmed that both __ and __ play a role in the geographic differences of phenotype

genetic variation; environment

95

fitness

the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

96

relative fitness

the contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus

97

natural selection acts on __, not __

phenotypes, not genotypes

98

the entity that is subjected to natural selection

the whole organism

99

the relative fitnes of a particular allele depends on

the entire genetic annd environmental context in which it is expressed

100

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

directional, disruptive, stabilizing selection

101

directional selection favors individuals that

deviate from the average

102

directional selection is most common when

a population's environment changes or when members of a population migrate to a new habitat with different environmental conditions than their former one

103

disruptive selection can be important in

the early stages of speciation

104

b/c most eukaryotes are diploid, a considerable amount of genetic variation is hidden from selection in the form of

recessive alleles

105

heterozygote protection maintains a huge pool of alleles that might not be favored under present conditions but

some of which could bring new benefits when the environment chages

106

balancing selection includes (2)

heterozygote advantage and frequency-dependent selection

107

balanced polymorphism

a situation in which two different versions of a gene are maintained in a population of organisms because individuals carrying both versions are better able to survive than those who have two copies of either version alone;

stable frequencies of 2 or more phenotypic forms in a population

108

balancing selection occurs when

natural selection maintains balanced polymorphism

109

heterozygote advantage

if individuals who are heterozygous at a particular gene locus have greater fitness than the homozygotes, natural selection will tend to maintain 2 or more alleles at that locus

110

frequency-dependent selection

in which the fitness of any 1 morph declines if it becomes too common in the population

111

neutral variation

differences that appear to confer no selective advantage

112

pseudogenes

genes that have become inactivated by mutations; where genetic "noise" is free to accumulate in all parts of the gene

113

sexual selection

natural selection for mating success. can result in sexual dimorphism

114

sexual dimorphism

marked differences between the sexes in secondary sexual characteristics, which aren't directly associated w/ reproduction (ex: differences in size, color, ornamentation)

115

intrasexual selection

selection within the same sex. direct competition among individuals of one sex for mates of the opposite sex. usually more obvious in males

116

intersexual selection

aka mate choice. in which individuals of one sex (usually females) are choosy in selecting their mates fro the other sex. in many cases, the female's choice depends on the showiness of the male's appearance/behhavior