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Chapter 23 Flashcards

1
Q

When is evolution apparent?

A

in changes in a population over time, not individual animals

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2
Q

What is microevolution? (2)

A

change in allele frequencies in a population over generations

Evolution in its smallest scale

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3
Q

What are the three main mechanisms of microevolution?

A

natural selection

genetic drift

gene flow

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4
Q

How does natural selection differ from genetic drift and gene flow in regards to microevolution?

A

The only mechanism that consistently improves the match between organisms and the environment

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5
Q

What is genetic drift?

A

chance events that alter allele frequencies

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6
Q

What is gene flow?

A

transfer of alleles between population

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7
Q

What is genetic variation?

A

Differences among individuals in the composition of their genes or other DNA sequences

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8
Q

How does genetic variation differ with the amount of genes?

A

Single gene- either-or effect is produced (purple or white flowers)

two or more genes- produces a difference in gradations along a continuum

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9
Q

How is gene variation quantified?

A

the average percentage of loci that are heterozygous

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10
Q

How can gene variation be measured in the molecular level?

A

nucleotide variation

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11
Q

Why doesn’t nucleotide variation always result in phenotypic variability?

A

differences occur within introns

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12
Q

What are five sources of genetic variation?

A

Mutation

Gene duplication

Production of new alleles and genes

Sexual reproduction

Produced rapidly by organisms with short generation times

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13
Q

How does new alleles arise?

A

mutation, or change in nucleotide sequence

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14
Q

Can mutations be predicted?

A

Cannot be predicted how and which DNA will be altered

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15
Q

Where does mutations occur, and how can it be passed down?

A

The majority of mutations occur in somatic cells in animals

Only mutations in gametes can be passed to offspring

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16
Q

What is point mutation, and an example?

A

change in one base

Ex- sickle cell disease

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17
Q

How beneficial or harmful are mutations?

A

Most mutations are slightly harmful

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18
Q

What is heterozygote protection?

A

when heterozygous individuals mask harmful recessive alleles

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19
Q

What is neutral variation?

A

point mutations in introns

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20
Q

How does gene duplication occur? (3)

A

Error in mitosis

Slippage during DNA replication

Activities of transposable elements

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21
Q

When are gene duplications harmful?

A

Large duplications can be harmful

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22
Q

How can small amounts of gene duplication affect genetic variation?

A

Smaller duplication may persist over generations and allow mutations

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23
Q

How is gene duplication correlated with evolution, and an example?

A

Played a major role in evolution

human ancestors had only one gene to smell, now we have 350

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24
Q

How can prokaryotes evolve quickly?

A

Prokaryotes have lower average mutations but have such more generations that variations arise quickly

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25
Why is HIV so hard to cure?
HIV mutates even more quickly since it has short generation times and RNA genome, making Single-drug treatment is less effective
26
How does gene variation arise from sexual reproduction?
Gene variation results from combination of alleles from parents
27
Methods during sexual reproduction where gene variation arises (3)
Crossing over Independent assortment of chromosomes fertilization
28
What is a population, and how are they separated?
a group of individuals of the same species that live in the same area and interbreed to produce fertile offspring isolated from others geographically
29
what is a gene pool?
all copies of every type of allele at every locus in all members of the population
30
What does a gene pool characterize?
Characterizes a population’s genetic makeup
31
What is frequency proportion?
number of specific allele/number of all allele x 100%
32
What is a fixed allele?
an allele existing for a particular locus in a population- all individuals are homozygous for this allele
33
What is the Hardy-Weinberg equilibrium? (2)
a population that is not evolving Allele and genotype frequencies will remain constant from generation to generation- only if Mendelian segregation and recombination of alleles at work
34
What is the Hardy-Weinberg equation?
P2 (homozygous dominant) + 2pq (heterozygous) + q2 = 1
35
How does the Hardy-Weinberg equation signify equilibrium?
The actual population of homozygous dominant must equal p2 and so on for the population to be in equilibrium
36
What are the conditions for Hardy-Weinberg equilibrium? (5)
no mutation random mating no natural selection extremely large population size no gene flow
37
What happens if conditions of the Hardy-Weinberg equilibrium is not met?
evolution occurs
38
How does mutation allow evolution?
A gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated
39
How does non-random mating allow evolution?
If individuals mate within a subset population, such as inbreeding, random mixing of gametes does not occur, and genotype frequencies change
40
How does natural selection allow evolution?
Differences in survival and reproductive success of individuals carrying different genotypes can alter allele frequencies
41
How does a small population size allow evolution?
The smaller the population, the more likely allele frequencies will fluctuate by chance from one generation to the next- aka genetic drift
42
How does gene flow allow evolution?
Moving alleles into or out of populations, gene flow can alter allele frequencies
43
How is the Hardy-Weinberg Equation applied?
in medicine ex- Estimating % of the population carrying alleles for inherited diseases like PKU
44
What does not alter allele frequency? (2)
New mutations non-random mating
45
Why doesn't new mutations alter allele frequencies?
Mutations are rare, so change is small
46
Why doesn't non-random mating alter allele frequencies?
Non-random mating can alter frequencies of homo/heterozygous, but not allele frequencies in the gene pool
47
What is natural selection based on?
differential success in survival and reproduction
48
What is natural selection?
Individuals exhibit variations in charitable traits, and traits more suited to the environment often produce more offspring
49
What does natural selection result in?
alleles being passed in proportions that differ
50
What is adaptive evolution?
an evolution that results in a better match between organisms and their environment
51
What is genetic drift?
chance events causing allele frequencies to fluctuate unpredictably from one generation to the next
52
What is genetic drift common in?
small populations
53
What is an example of genetic drift?
white flowers being accidentally killed, leading to less white-flowered offspring
54
What increases chance of deviation from predicted results?
The smaller the number of events that occur
55
What is does small population lead to?
over/underrepresentation of an allele in the next generation
56
What two things can genetic drift cause?
allele frequencies to change at random harmful alleles to become fixed
57
What can genetic drift lead to?
loss of genetic variation within populations
58
What is the founder effect?
when few individuals become isolated from a larger population, a smaller group can establish a new population with a different gene pool
59
What does the founder effect account for?
a high frequency of certain inherited disorders in isolated human populations
60
What is the bottleneck effect?
a sudden change in environment, like a flood, drastically reducing the size of the population
61
What is gene flow?
transfer of alleles into or out of a population due to movement of fertile individuals or their gametes
62
What can gene flow result in?
two populations combining into a single population with a common gene pool
63
What can natural selection increase?
frequencies of alleles that provide reproductive advantage
64
What is relative fitness?
contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
65
What does relative fitness act on?
more directly on the phenotype than on the genotype
66
What does selection favor?
heritable phenotypic traits that provide higher reproductive success
67
What is directional selection?
when conditions favor individuals exhibiting one extreme of a phenotypic range
68
What is a directional selection frequency curve?
Shifts the population’s frequency curve of phenotypic character in one direction or the other
69
When is directional selection common, and an example?
Common when the environment changes or when members migrate to a new habitat Ex- Galapagos finches
70
What is disruptive selection?
when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
71
What is an example of disruptive selection?
two beak sizes in one species One for soft seeds, the other for hard seeds Medium-sized beaks are inefficient in feeding on both
72
What is stabilizing selection?
acts against both extreme phenotypes and favors intermediate variants
73
What does stabilizing selection reduce?
Reduces variation and tends to maintain the status quo of a phenotype
74
What is an example of stabilizing selection?
baby weight, with smaller and larger weights having higher mortality
75
How does adaptations arise?
gradually as natural selection increases frequencies of alleles that enhance survival and reproduction
76
What kind of process is adaptive evolution, and why?
Since the environment changes over time, adaptive evolution is a continuous dynamic process
77
How does genetic drift affect adaptive evolution?
can both increase and decrease beneficial allele frequency
78
How does genetic flow affect adaptive evolution?
introduce both advantageous and disadvantageous alleles
79
What is sexual selection?
natural selection which individuals with certain inherited characteristics are more likely than other individuals to obtain mates
80
What is sexual dimorphism, and examples (2)?
difference in secondary sexual characteristics between males and females of the same species Ex- size, color, ornamentation, behavior
81
What is intrasexual selection, and what is it common in?
selection within the same sex, competing directly for mates of the opposite sex Common in males
82
What is intersexual selection, and what is it common in?
individuals of one sex being choosy in selecting their mates from the opposite sex Often in female
83
Why did female preferences evolve? (2)
Female preferences for certain male characteristics may have evolved because the traits are correlated with good genes “Attractive” male traits may be related to overall health as well
84
Why can't natural selection cut all unfavorable alleles?
because recessive alleles are hidden in heterozygotes
85
What is balancing selection?
selection preserving variation at some loci, maintaining two or more forms in a population
86
What does balancing selection include?
Includes heterozygote advantage and frequency-dependent selection
87
What is heterozygote advantage?
when heterozygotes have greater fitness than either kind of homozygotes
88
How does natural selection correlate with heterozygote advantage?
Natural selection tends to maintain two or more alleles at certain loci
89
What is heterozygote advantage defined in?
terms of genotype
90
What kind of selection is heterozygote advantage?
Either a stabilizing or direction selection, depending on phenotype advantage
91
What is an example of heterozygote advantage?
sickle cell Heterozygotes are protected from the severe effects of malaria
92
What is frequency-dependent selection?
fitness of a phenotype depends on how common it is in the population
93
What is an example of frequency-dependent selection?
scale eating fish oscillate between right and left mouths in response to prey guarding against the specific side
94
How does natural selection operate?
on a “better than” basis
95
Four reasons why natural selection cannot fashion perfect organisms
Selection can act only on existing variation Evolution is limited by historical constraints Adaptations are often compromises Chance, natural selection, and the environment interact
96
How does natural selection act on existing variation?
Favors only the fittest phenotype currently in the population, which may not be the ideal trait
97
How is evolution limited by historical constraints?
Evolution only operates on traits an organism only has, working on existing structure
98
What is an example of adaptation compromise?
flexible limbs allow versatility, but make us prone to sprains, torn ligaments, and dislocation
99
How does chance and natural selection interact, and an example?
Chance events affect the evolution of the population Ex- storm can transport insects to an unfavorable environment
100
How does the environment and natural selection interact?
The environment at a location can change unpredictably from year to year

BI158 (16 decks)

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