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23 Flashcards

1
Q

how does natural selection act on individuals

A

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

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2
Q

____ are selected; ____ evolve

A

individuals; populations

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3
Q

microevolution

A

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

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4
Q

darwin didn’t have a satisfactory explanation for

A

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

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5
Q

model proposed by gregor mendel

A

particular hypothesis of inheritance

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

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6
Q

darwin considered the raw material for natural selection to be

A

“quantitative” characters – those characteristics in a population that vary along a continuum

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7
Q

mendel and other early geneticists worked only with

A

discrete “either-or” traits

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8
Q

geneticists later determined that

A

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

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9
Q

population genetics

A

the study of how populations change genetically over time

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10
Q

population genetics gave rise to ____

A

modern synthesis

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11
Q

modern synthesis

A

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

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12
Q

population

A

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

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13
Q

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

A

confined to different,. widely separated islands or lakes

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14
Q

individuals near the population center are more likely to breed with

A

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

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15
Q

gene pool

A

the aggregate of genes in a population at any one time

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16
Q

the gene pool consists of

A

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

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17
Q

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

A

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

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18
Q

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

A

individuals may be either homozygous or heterozygous

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19
Q

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

A

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

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20
Q

at loci that have more than 2 alleles,

A

the sum of all allele frequencies must still equal 1

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21
Q

hardy-weinberg theorem was derived in the year

A

1908

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22
Q

the hardy-weinberg theorem describes

A

the properties of gene pools that aren’t evolving

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23
Q

the hardy-weinberg theorem states that

A

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

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24
Q

the hardy-weinberg theorem describes how

A

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

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25
Q

the hardy-weinberg theorem lays the groundwork for

A

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

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26
Q

the preservation of genetic variation provides the opportunity for

A

natural selection to act over many generations

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27
Q

the allele frequencies in all the gametes produced by the population

A

will be the same as in the original population

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28
Q

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

A

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

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29
Q

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

A

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

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30
Q

a population ________ for its allele frequencies to remain constant

A

doesn’t need to be in hardy-weinberg equilibrium

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31
Q

raw material of evolutionary change

A

genetic variation

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32
Q

conditions for hardy-weinberg equilibirum

A
  1. extremely large population size
  2. no gene flow
  3. no mutations
  4. random mating
  5. no natural selection
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33
Q

genetic drift

A

chance fluctuations in allele frequencies from one generation to the next

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34
Q

the smaller the population, the greater

A

the role played by genetic drift

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35
Q

gene flow

A

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

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36
Q

gene flow can

A

alter allele frequencies

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37
Q

why do mutations modify the gene pool?

A

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

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38
Q

if individuals preferentially choose mates with certain genotypes,

A

random mixing of gametes doesn’t occur

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39
Q

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

A

evolution

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40
Q

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

A

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

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41
Q

the hardy-weinberg equation can be used to

A

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

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42
Q

PKU

A

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

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43
Q

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

we must also neglect

A

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

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44
Q

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

A

mutation and sexual recombination

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45
Q

____ and ____ originate only by mutations

A

new genes and new alleles

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46
Q

mutations

A

changes in the nucleotide sequence of DNA

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47
Q

most mutations occur in

A

somatic cells and are lost when the individual dies

48
Q

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

A

cell lines that produce gametes,

only a small fraction of these spread through populations

49
Q

point mutation

A

change of one base in a gene

50
Q

most point mutations are

A

probably harmless

51
Q

why are most point mutations harmless?

A

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
Q

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

A

noncoding regions of DNA that regulate the expression of genes

53
Q

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

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

A

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

leave genes intact

54
Q

duplications of chromosome segments are

A

nearly always harmful

55
Q

smaller pieces of DNA are often introduced into a genome through

A

the activity of transposable elements

56
Q

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

A

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

57
Q

exons

A

coding portions of genes

58
Q

new genes may also arise when

A

exons are shuffled within the genome

59
Q

______ appear to have played a major role in evolution

A

beneficial increases in gene number

60
Q

mutation rates

A

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

61
Q

mutations can rapidly generate genetic variation in

A

microorganisms and viruses with short generation spans

62
Q

HIV has a generation span of

A

about 2 days

63
Q

an RNA genome has

A

a much higher mutation rate than a typical DNA genome

64
Q

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

A

sexual recombination; mutation

65
Q

nearly all phenotypic variations based on genetic differences result fro m

A

recombinational shuffling of the existing alleles in the gene pool

66
Q

bacteria and many viruses can also undergo recombination, but

A

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

67
Q

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

A

evolve rapidly through extensive recombination; high mutation rates

68
Q

although new mutations can modify allele frrequencies,

A

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

69
Q

what does recombination do?

A

it reshuffles alleles but doesn’t change their frequencies

70
Q

effect of nonrandom mating

A

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

71
Q

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

A

natural selection, genetic drift, and gene flow

72
Q

result of natural selection in terms of alleles?

A

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

73
Q

over time, genetic drift tends to

A

reduce genetic variation through losses of alleles from the gene pool

74
Q

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

A

the bottleneck effect and the founder effect

75
Q

bottleneck effect

A

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
Q

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

A

the population is large enough that chance fluctuations have less effect

77
Q

founder effect

A

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
Q

gene flow tends to

A

reduce differernces between populations

79
Q

discrete characters often are determined by

A

a single gene locus with different alleles that produce distinct phenotypes

80
Q

most heritable variation consists of

A

quantitative characters

81
Q

heritable quantitative variation results from

A

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

82
Q

morphs

A

different forms that result when individuals differ in a discrete character

83
Q

phenotypic polymorphism

A

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
Q

genotypic polymorphism

A

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

85
Q

population geneticists measure the number of polymorphisms in a population by

A

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

86
Q

average heterozygosity

A

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

87
Q

nucleoitde variability is measured by

A

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

88
Q

why does average heterozygosity tend to be greater than nucleotide variability

A

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
Q

based on measurements of nucleotide variability, humans have

A

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

90
Q

geogrphic variation

A

differences between the gene pools of separate populations or population subgroups

91
Q

most species exhibit _____ variation

A

geographic

92
Q

cline

A

a graded change in a trait along a geographic axis

93
Q

in some cases, a cline may represent

in other cases,

A

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

a gradation in some environmental variable may prorudce a cline

94
Q

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

A

genetic variation; environment

95
Q

fitness

A

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

96
Q

relative fitness

A

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

97
Q

natural selection acts on __, not __

A

phenotypes, not genotypes

98
Q

the entity that is subjected to natural selection

A

the whole organism

99
Q

the relative fitnes of a particular allele depends on

A

the entire genetic annd environmental context in which it is expressed

100
Q

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

A

directional, disruptive, stabilizing selection

101
Q

directional selection favors individuals that

A

deviate from the average

102
Q

directional selection is most common when

A

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
Q

disruptive selection can be important in

A

the early stages of speciation

104
Q

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

A

recessive alleles

105
Q

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

A

some of which could bring new benefits when the environment chages

106
Q

balancing selection includes (2)

A

heterozygote advantage and frequency-dependent selection

107
Q

balanced polymorphism

A

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
Q

balancing selection occurs when

A

natural selection maintains balanced polymorphism

109
Q

heterozygote advantage

A

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
Q

frequency-dependent selection

A

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

111
Q

neutral variation

A

differences that appear to confer no selective advantage

112
Q

pseudogenes

A

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

113
Q

sexual selection

A

natural selection for mating success. can result in sexual dimorphism

114
Q

sexual dimorphism

A

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

115
Q

intrasexual selection

A

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

116
Q

intersexual selection

A

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

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