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Genetics > Chapter 27 > Flashcards

Chapter 27 Flashcards

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1
Q

What is population genetics?

A

extent of genetic variation within a group of individuals and changes in that variation over time (focus shifted away from individual and toward population of which the individual is a member)

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2
Q

What is the gene pool?

A

All alleles of every gene in a population (only individuals that reproduce contribute to gene pool of next generation)

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3
Q

What is the goal of population geneticists?

A

Make predictions about how generations change due to genetic variation within the gene pool

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4
Q

What is a population?

A

group of individuals of the same species that occupy the same region and can interbreed with each other

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5
Q

What are local populations?

A

smaller groups within a population, often separated by moderate geographic barriers (ex: deer in ohio different from deer in new massachusetts)

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6
Q

What are three ways a population may change?

A

size, geographic location, genetic composition

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7
Q

What is polymorphism?

A

refers to observation that many traits display variation within a population (ex: Hawaiin happy-face spider that differ in alleles that affect color and pattern)

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8
Q

How can a gene be described that commonly exists as 2 or more alleles in a population?

A

Polymorphic
(monomorphic gene exists predominantly as a single allele)

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9
Q

What is a single-nucleotide polymorphism (SNP)?

A

A change in single base pair in DNA, SNPs account for 90% of variation among people, may not lead to change in phenotype

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10
Q

What is an example of SNP?

A

Sickle cell disease caused by a deletion that eliminates function

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11
Q

What is the equation for allele frequency?

A

Allele Frequency = (Number of copies of an allele in a population) / (Total number of alleles for that gene in a population)

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12
Q

What is the equation for genotype frequency?

A

Genotype frequency = (Number of individuals with a particular genotype in a population) / (Total number of individuals in a population)

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13
Q

Are polymorphisms common or rare in natural populations?

A

very common

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14
Q

What is the Hardy-Weinberg equation?

A

simple mathematical expression that relates allele and genotype frequencies in a population, also called an equilibrium (no evolution/change)
p^2 + 2pq + q^2 = 1
(p is dominant and q is recessive)

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15
Q

A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D?

A

0.24

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16
Q

The allele frequency of C is 0.4 and that of c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes?

A

0.48

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17
Q

Which of the following is a factor that, by itself, does not promote widespread changes in allele or genotype frequencies?
a. new mutation
b. natural selection
c. genetic drift
d. migration
e. nonrandom mating

A

a. new mutation

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18
Q

What are the five conditions required to reach equilibrium?

A

no new mutations, no genetic drift (no change of frequencies due to chance alone), no migration, no natural selection, random mating

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19
Q

What is the null hypothesis in HW equilibrium?

A

No change/evolution

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20
Q

If null hypothesis is not rejected, you can accept the hypothesis that the population is __________.

A

in equilibrium

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21
Q

If the null hypothesis is rejected, the population is __________.

A

in disequilibrium

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22
Q

What is microevolution?

A

describes changes in a population’s gene pool from generation to generation, driven by: mutation, random genetic drift, migration, natural selection, nonrandom mating (everything opposite HW)

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23
Q

In the theory of natural selection, phenotypes may vary with regard to their _____________.

A

reproductive success

24
Q

What is fitness?

A

Measure of reproductive success in relative fitness values (ω), relative likelihood that a genotype will survive and contribute to gene pool of next generation

25
Q

For calculating fitness values, the gene with the highest reproductive ability (most offspring) is given a fitness value of _____.

A

1.0

26
Q

Does natural selection act on genotypes or phenotypes?

A

Phenotypes

27
Q

Directional selection

A

Favors survival of one extreme phenotype that is better adapted to an environmental condition (choosing one phenotype as more fit)

28
Q

Balancing selection

A

Favors maintenance of two or more alleles (heterozygote advantage)

29
Q

Disruptive (or diversifying) selection & example

A

Favors survival of two (or more) different phenotypes
Caused by fitness values for a given genotype that vary in different environments
Example: snail that lives in woods (brown color favored on soil, pink shell favored on leaf litter) and open fields (yellow color favored)

30
Q

Stabilizing selection & example

A

Favors survival of individuals with intermediate phenotypes
Tends to decrease genetic diversity
Example: laying eggs

31
Q

Mean fitness of the population & equation

A

Measure of how fit the whole population is
p^2wAA + 2pqwAa + q^2waa = w (with bar on top)
Divide both sides by mean fitness and the equation will be set equal to 1 (slide 29)

32
Q

Natural selection raises the _________ of the population from one generation to the next.

A

mean fitness

33
Q

What is the selection coefficient equation

A

measures the degree to which a genotype is selected against
s = 1 - w
w is fitness

34
Q

What is negative frequency-dependent selection?

A

type of balancing selection, rare individuals have a higher fitness than more common individuals; more likely to reproduce, selection always favors less numerous genotype

35
Q

Name and example of frequency-dependent selection

A

Rewardless flower - relative fitness of the less-common flower increases

36
Q

Genetic drift

A

random changes in allele frequencies due to random fluctuations, just chance based
Favors either loss or fixation of an allele
Less effect on large populations, rate depends on population size

37
Q

Expected number of new mutations (genetic drift) equation

A

Expected number of new mutations = 2Nu (if each individual has two copies of the gene of interest)
u = mutation rate
N = number of individuals in population
New mutation more likely to occur in large populations

38
Q

Probability of fixation of a newly arising allele due to genetic drift =

A

1/2N

39
Q

What are the effects on mutations and fixations due to value of N in genetic drift?

A

Large N: new mutation more likely but has greater chance of being eliminated due to random genetic drift
Small N: new mutations less likely but has greater chance of being fixed in pop.

40
Q

Equation for number of generations it takes for fixation

A

t (with line on top) = 4N
N is number of individuals in population assuming that males and females equally contribute

41
Q

Bottleneck effect

A

Natural disaster randomly eliminates individuals regardless of phenotype

42
Q

Founder effect

A

Small group of individuals separates from larger population and establishes colony in new location
2 important consequences:
founding population is expected to have less genetic variation than original pop., founding pop. will have allelic frequencies that may differ markedly from original pop. as matter of chance

43
Q

Gene flow

A

Transfer of alleles from donor pop. to recipient pop., changing its gene pool
Recipient pop. called conglomerate

44
Q

Equation for calculating change in allele frequency in conglomerate pop.

A

delta pc = m(pD - pR)
delta pc: change in allele frequency in conglomerate population
pD: allele frequency in donor pop.
pR: allele frequency in original recipient pop.
m: proportion of migrants in conglomerate pop.
m=(number of migrants in conglomerate pop.)/(total number of individuals in conglomerate population)
pc = pR +delta pc

45
Q

Bidirectional migration

A

Tends to reduce allele frequency differences between populations and can enhance genetic diversity within population

46
Q

Assortative mating (positive and negative)

A

Individuals don’t mate randomly
Positive - more likely to mate due to similar phenotypic characteristics
Negative - individuals with dissimilar phenotypes mate preferentially

47
Q

Inbreeding

A

mating between genetically-related individuals, decreases overall diversity, gene pool smaller

48
Q

Outbreeding

A

mating between genetically unrelated individuals

49
Q

Inbreeding/fixation coefficient (F)

A

Degree of relatedness in pedigree, probability that gene in inbred individual is homozygous due to its inheritance from common ancestor
F = sum of ((1/2)^n (1+FA))
n: number of individuals in inbreeding path (excluding inbred offspring)
FA: breeding coefficient of common ancestor

50
Q

Inbreeding example, frequencies of A and a are p and q

A

p^2 + fpq = frequency of AA
2pq(1-f) = frequency of Aa
q^2 + fpq = frequency of aa

51
Q

Inbreeding depression

A

Inbreeding in natural populations will lower overall fitness

52
Q

Ways to change genetic variation

A

syke
slide 75 has massive chart

53
Q

Out of beneficial, neutral, and deleterious mutations, which is most likely?

A

Neutral and deleterious far likelier

54
Q

Mutation rate

A

probability that a gene will be altered by new mutation
delta q = up
u: mutation rate of an allele into a different allele
q: allele frequency of new allele
p: allele frequency of current allele

55
Q

To calculate the change in allele frequency after any number of generations:

A

(1-u)^t = pt/p0
u: the mutation rate of the conversion of original allele to new allele
t: the number of generations
p0: the frequency of original allele in the starting generation
pt: the frequency of allele original allele after t generations

56
Q

Mutations are important fro evolution but has ______ impact in changes of allele frequency.

A

negligible

57
Q

check slide 49

A

Genetics (13 decks)

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