Module 13-15 Alteration of Genetic Equilibrium Flashcards

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1
Q

These are processes that cause a change in gene frequency magnitude and degree.

A

Systematic processes (Ex. Mutation, selection and migration)

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2
Q

These are processes that change the magnitude but not the direction

A

Dispersive Processes (Genetic Drift and nonpanmictic/nonrandom mating)

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3
Q

This is the ultimate source of genetic variation inclusive of all genetic changes.

A

Mutation

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4
Q

T/F Mutation occurs at a generally very low rate per generation.

A

T, 10^-5 or 10^-6 per generation in most loci of most organisms

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5
Q

Two types of mutation and differentiate

A

Non-recurrent: Rare, small chance of survival

Recurrent: Consequence of altering gene frequencies

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6
Q

If p0 is the initial frequency of gene A and it mutates continuously to a at a rate, and the reverse mutation does not occur, A after n generations becomes pn. How is pn calculated?

A

pn=po*(1-u)^n

where:
pn = freq of A after n generations
po = initial freq of A
u = rate of mutation
n = number of generations

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7
Q

Given initial A and a frequencies p and q, how will you calculate new frequencies with forward and backward mutations after 1 generation?

A

freq (A) = p1 = p + (vq) - (up)
freq (a) = q1 = q + (up) - (vq)

where:
u is the forwards rate
v is the reverse rate

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8
Q

How do you calculate for p and q at mutational equilibrium?

A

At mutational equilibrium, up=vq therefore

p = v/(u+v) and q = u/(u+v)

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9
Q

Using mutational equilibrium, how do you calculate the value of q after any specified generation time with both forward and backward mutation?

A

(u+v)n=ln((q-qe)/(qn-qe))

where:
q = initial q value
qe = q freq at mutational equilibrium
qn = q after n generations

Algebra go brrrr

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10
Q

Refers to fluctuations in allele frequency that occur by chance, particularly in small populations, as a result of random sampling among gametes.

A

Random Genetic Drift

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11
Q

Two Causes of Random Genetic Drift

A

Mendelian Segregation

Finite population size

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12
Q

How to calculate variance in allelic frequency among populations under random genetic drift? What about sampling error?

A

(sp)^2 = (pq)/2N

where:
N = total population size
p and q = allelic freqs of p and q
(sp)^2 = Variance

To get sampling error/standard dev, get square root of Variance.

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13
Q

The number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration

A

Effective Population Size

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14
Q

Causes of genetic drift (3)

A

Population size reduction by environmental factors

Founder Effect

Genetic Bottleneck

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15
Q

Occurs when a population is established by a small number of individuals resulting in significantly less genetic diversity

A

Founder Effect

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16
Q

Occurs when a population undergoes a drastic reduction in population size. Emphasis on drastic

A

Genetic Bottleneck

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17
Q

Four Main Aspects of Random Genetic Drift

A

▪direction is unpredictable

▪magnitude depends on population size

▪long-term effect is to reduce genetic variation within a population

▪causes populations to diverge

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18
Q

Composite of the forces that limit the reproductive success of a genotype

A

Selection

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19
Q

Comparative ability of a genotype to withstand selection

A

Fitness

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20
Q

The extent to which a genotype contributes to the offspring of the next generation relative to the other genotypes in a given environment

A

Adaptive Value (W)

Also known as fitness or Selective Value

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21
Q

This is the percentage reduction in fitness.

A

Selection Coefficient (s)

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22
Q

What is the relationship between Adaptive Value (W) and selection coefficient (s)?

A

W=1-s or s=1-W

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23
Q

In calculating the frequency of genotypes before and after selection, assuming Hardy-Weinberg proportions before selection, what are the steps?

A
  1. Get frequency before selection p^2, 2pq, and q^2
  2. Multiply by their respective selection coefficients to get their weighted contributions
  3. Sum all weighted contributions to get the weighted total
  4. Divide the weighted contributions by the weighted total to get the frequency after selection
24
Q

Calculation of Change in Frequency (Delta q) of Gene a when |s|= 1 (homozygous recessive is lethal) for Homozygous Recessive Genotype

A

Delta q = -q^2/(1+q)

Applicable when aa is lethal

25
Q

Calculation of Change in Frequency of a (Delta q) for a Gene with Varying Degrees of Deleterious Effects (0<s<1)

A

Delta q = ((-sq^2)(1-q))/(1-(q^2 * s))

Applicable when 0<s<1

For summarized formulas, just check slide 11 from module 14

26
Q

Calculation of Change in Frequency of A (Delta p) for a Gene with Varying Degrees of Deleterious Effects on the Dominant Allele. Let t be the selection coefficient for p

A

Delta p = (-tp(1-p)^2)/(1-tp(2-p))

For summarized formulas, just check slide 11 from module 14

27
Q

Calculation in Change in Frequency of Gene a (Delta q) in One Generation of Selection in which the Heterozygotes have Adaptive Value of 1 and the Homozygous Selected Against by t and s, respectively.

A

Delta q = (pq(pt-qs))/(1-(tp^2)-(sq^2)

For summarized formulas, just check slide 11 from module 14

28
Q

How to calculate for change in q (Delta q) with complete dominance (selection against a)?

A

Delta q = ((-sq^2)(1-q))/(1-sq^2)

Slide 15 on Module 14

29
Q

How to calculate for change in q (Delta q) with complete dominance (selection favoring a)?

A

Delta q = ((sq^2)(1-q))/((1-s) (1-q^2))

Slide 16 on Module 14

30
Q

Let A1 and A2 donate two alleles for 1 gene. How do you calculate for change in q (Delta q) with no dominance (selection against A2).

A

Delta q = (0.5*sq(1-q))/(1-sq)
Slide 17 on Module 14

31
Q

Let A1 and A2 donate two alleles for 1 gene. How do you calculate for change in q (Delta q) with no dominance (selection favoring A2).

A

Delta q = (0.5*sq(1-q))/(1-s+qs)
Slide 17 on Module 14

32
Q

How do you calculate for the allele frequency of q after n amount of generations assuming s=1 and there is no mutation?

A

qt = q/(1+tq)

Where:
q = initial q frequency
t = number of generations to change q to qt
qt = you, jk, its the final q allele frequency

Note: Only use when s=1 (Selection is against homozygous recessive, no mutation)

33
Q

At equilibrium the change due to mutation will be equal and opposite to the change due to selection (Delta q mutation = - Delta q selection)

At mutation/selection equilibrium, q can be calculated how?

A

qe=sqrt(u/s)

Where:
u = mutation rate
s = selection coefficient.

34
Q

What are the three types of selection and what do they select against/for

A

Stabilizing Selection - Selects against extremes, selects for intermediate phenotype

Directional Selection - Selects for a particular genotype

Disruptive Selection - Selects against the intermediate phenotype, selects for the extremes.

35
Q

What are the implications of stabilizing selection

A

Increased fitness of intermediate phenotype favors adaptation to existing environmental conditions but reduces phenotypic and genotypic diversity

36
Q

What are the implications of Disruptive selection

A

Increased fitness of extreme phenotypes results in higher phenotypic and genetic diversity resulting in a population with a bimodel distribution

37
Q

Can be thought of as two special kinds of natural selection, competition and preference

A

Sexual Selection

38
Q

Offers explanations for the evolution of large human brains and behaviors such as humor, music, and poetry that do not have obvious survival value

A

“mating-mind” hypothesis

39
Q

Technical term for altruistic behavior that has been shown, or is theoretically supposed, to be explained by kin selection or self sacrifice methods

A

Kin Altruism

Nepotism or favor towards own kin is needed for kin-selection to occur

40
Q

This is the mathematical explanation of kin selection. What is the name and formula?

A

Hamilton’s Rule

rB>C

Where:
r = Genetic relatedness of recipient to actor
B = Additional reproductive benefit gained by recipient
C = Reproductive cost to actor

41
Q

Also known as gene flow, this is the influx of genes from other populations leading to decreased genetic divergence and increased genetic variation between and within populations

A

Migration

42
Q

In a population of 600 natives with a q frequency of q_o=0.2, 400 immigrants with a q frequency of q_m=0.6 were assimilated. What is the frequency of q in the mixed population (q1) and the change in frequency?

A

Given:
400 immigrants, 600 natives
q_m = 0.6, q_o = 0.2

Required: q1 and Delta q

Solution:
Get m, the proportion of immigrants in the mixed.
Use the formula
q1 = mq_m+(1-m)q_o

m=400/(600+400)=0.4
q1 = 0.4(0.6)+(1-0.4)0.2
q1= 0.36

Delta q = q1-q_o = 0.36-0.2 = 0.16

43
Q

The value of q after n generations of migration is provided by the formula

A

q_n - q_m = (1-m)^n (q_o - q_m)

Algebra go brrr

44
Q

Percentage of alleles contributed by the migrants (or proportion of gene flow/admixture) can be calculated by this formula:

A

m = (q_o-q1)/(q_o-q_m)

45
Q

Matings between closely related individuals that leads to an increase in the proportion of homozygotes and a decrease in the proportion of heterozygotes

A

Inbreeding

46
Q

This is the avoidance of mating between related individuals

A

Outcrossing

47
Q

Result from increased homozygosity for heterozygous alleles and is associated with reduced fitness and lower survival rates among the offspring

A

Inbreeding Depression

48
Q

Measures the extent of inbreeding occurring in a population and the probability that two alleles of a given gene in an individual are derived from a common ancestral allele or are identical by descent.

A

Inbreeding Coefficient (F)

49
Q

if 2 alleles in an inbred individual are identical by descent, the genotype at the locus is said to be (a) otherwise it is said to be (b).

A

(a) Autozygous
(b) Allozygous

50
Q

When inbreeding occurs, the heterozygote frequency is _______ at each generation

A

halved

51
Q

At HWE, how do you solve for the inbreeding coefficient F?

A

F= 1- (Ho/He)
which can be further expanded to
F=1-(Ho/2pq) = (2pq-Ho)/2pq

52
Q

Genotype frequencies when inbreeding occurs can be calculated by

A

AA:p^2 (1-F) + pF or p^2 +pqF
Aa:2pq(1-F)
aa:q^2 (1-F) + qF or q^2 +pqF

53
Q

Xeroderma pigmentosum (XP) is an often-fatal skin cancer resulting from a recessive mutant allele that affects DNA repair. In the United States, the frequency of homozygous- recessive affected people is approx. 1 in 250,000.

What is the expected frequency of XP among the offspring of first-cousin matings?

A

Given: q^2 = 1/250000, First Cousins

Required: f(aa)

Solution:
First Cousins: F=1/16
q^2 = 0.000004->q=0.002
p=1-0.002=0.998

f(aa) = q^2 +pqF = 0.000004 + (0.998)(0.002)(1/16)

f(aa) = 0.000129

54
Q

Xeroderma pigmentosum (XP) is an often-fatal skin cancer resulting from a recessive mutant allele that affects DNA repair. In the United States, the frequency of homozygous- recessive affected people is approximately 1 in 250,000. It was found that frequency of XP among offspring of first-cousin matings was f(aa) = 0.000129

What is the ratio of XP among the offspring of first- cousin matings to that among the offspring of nonrelatives?

A

Given:
Inbred f(aa) = 0.000129
Outbred f(aa) = 0.000004

Required: inbred/outbred

Solution:
0.000129/0.000004 = 32

55
Q

Mating pattern in which similar phenotypes mate with one another more frequently than what is expected.

A

Assortative Mating (Homogamy)

A_ x A_ and aa x aa

56
Q

Mating Pattern where in dissimilar phenotypes mate with one another more frequently than what is to be expected

A

Disassortative Mating (Heterogamy)

A_ x aa