Hardy-Weinberg Calculations Flashcards

1
Q

Hardy-Weinberg Law

A

genotypes are distributed in proportion to frequencies of individual alleles in a population and remain constant from generation to generation so long as the population is in equilibrium

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2
Q

Allele frequencies

2, 3, and 4 alleles

A

2: p + q = 1
3: p + q + r = 1
4: p + q + r + s = 1

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3
Q

Genotype frequencies (2, 3, and 4 alleles)

A

2: p^2 + 2pq + q^2 = 1
3: p^2 + q^2 + r^2 + 2pq + 2pr + 2qr = 1
4: p^2 + q^2 + r^2 + s^2 + 2pq + 2pr + 2ps + 2qr + 2qs + 2rs = 1

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4
Q

HW in AD conditions

A
  • frequency of mutant gene (q) = 1/2 incidence of disease (2pq)
  • p^2 often lethal, so p approximates 0
  • if incidence of disease is 1 in 10,000 (2pq), frequency of disease allele is 1 in 20,000
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5
Q

HW in AR conditions

A
  • frequency of disease allele (q) is the square root of disease incidence (q^2)
  • p approximates 1
  • carrier frequency = 2q
  • if incidence of disease is 1 in 2500, q = 1 in 50 and 2pq = 1 in 25
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6
Q

HW in XLR conditions

A
  • because males are hemizygous, incidence of disease = q
  • p approximates 1
  • because females have two X’s, p^2 + 2pq + q^2 can be used
  • if incidence of disease in 1 in 40, q = 1 in 40; carrier frequency in females is 1 in 20 and expected number of affected females is 1 in 160
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7
Q

Fitness (f)

A

probability of transmitting one’s genes to the next generation compared to the average probability for the population

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8
Q

Coefficient of selection (s)

A

measure of the loss of fitness

s = 1 - f

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9
Q

Mu

A
  • frequency of an allele in a population represents balance between mutation rate of gene (mu) and effects of selection against allele; as selection changes, allele frequency changes
  • Mu = q * s, where s = 1 - f and q calculated based on inheritance pattern of condition
  • Mu can be calculated by counting cases due to new mutations directly
  • Mu = (# cases with new mutations)/(2 x total sample size)
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10
Q

Assumptions of HW

A
  • random mating
  • no selection
  • no new mutations
  • no migration
  • population infinitely large
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11
Q

Exceptions to the Assumptions

A
  • non-random mating (assortative mating, population stratification, consanguinity)
  • selection does happen (heterozygote advantage/disadvantage)
  • new mutations do happen, but they are rare
  • gene flow/population admixture
  • genetic drift (founder effect, population bottleneck)
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