Quantitative Genetics

Question 1

H-W assumptions

Answer 1

1. random mating
2. no selection-all genotypes equally viable and no selection for or against a phenotype
3. no new mutations
4. population is infinitely large
5. no migration

Question 2

assortative mating

Answer 2

choosing a mate who has the same (positive) or opposite (negative) trait or genotype
-ex: individuals with deafness or achondroplasia

Question 3

population stratification

Answer 3

presence of a systematic difference in allele frequencies within population subgroups related to the fact that matings across divisions are more common than matings within divisions (ex: African Americans and US Caucasians)

Question 4

founder mutations

Answer 4

increased allele frequency or disease allele in a population related to the fact that it is more common to inter-marry within the population (ex: BRCA1/2 in AJ, alpha thal in SE Asians and Mediterranean pops)

Question 5

consanguinity

Answer 5

shared common ancestry predisposes individuals to sharing more alleles that are identical-by-descent, than would be expected in a randomly mating population
-increased risk for AR conditions

Question 6

coefficient of inbreeding (F)

Answer 6

probability that a person who is homozygous at a particular locus inherited both from a common ancestor; proportion of loci at which an individual is IBD

Question 7

coefficient of relationship (r)

Answer 7

measure of the degree of consanguinity; amount of shared DNA

Question 8

consanguinity between third cousins

Answer 8

degree of relationship at this point or further apart is not considered genetically significant

Question 9

non-random mating

Answer 9

tends to increase the proportion of homozygotes and decrease the proportion of heterozygotes

Question 10

fitness (f)

Answer 10

probability of an individual to transmit their genes to the next generation compared to the average probability for the population

Question 11

coefficient of selection (s)

Answer 11

-measurement of the loss of fitness

=1-f

Question 12

mutation rate of the gene (µ)

Answer 12

equal to the selection against the allele (s) and (multiplied by) its frequency in the population (q)

Question 13

f=0

Answer 13

complete selection against an allele and all affected individuals result from new mutation (ex: thanatophoric dysplasia)

Question 14

f=1

Answer 14

no deleterious effect on reproduction for carriers of the allele; means s=0 and there is no selection against it and nearly all affected individuals inherit allele from parent (ex: HD)

Question 15

0

Answer 15

proportion of affected individuals come from carrier parents, while others result from new mutation

Question 16

selection in AR conditions

Answer 16

less effective because it takes many generations to decrease the mutant frequency and fitness is normal due to unaffected carriers
-medical treatments do no effect frequencies significantly

Question 17

heterozygote advantage

Answer 17

example of balancing selection that results in a relatively high allele frequency due to selective forces acting both for and against an allele
-ex: sickle trait in malaria protection

Question 18

heterozygote disadvantage

Answer 18

allele reduces the reproductive fitness of a carrier, but is still maintained in the population because it does not completely inhibit the production of offspring
-ex: pericentric inversion carriers have more risk for miscarriage, Rh-negative mothers predispose Rh-positive fetus to HDN

Question 19

genetic drift

Answer 19

pool of gametes formed for next generation represents a random sample of alleles from the population

• frequency in variations are due to random sampling
• effects in smaller populations can be powerful, in large populations usually negligible

Question 20

founder effects/bottleneck

Answer 20

genetic isolation/genetic drift occurs either by separation of a few individuals or shrinking of population, which can lead to a higher incidence of an allele or condition
-ex: EVC in Penn Dutch, HD in Venezuelan pop, tyrosinemia in FC

Question 21

gene flow or population admixture

Answer 21

non-random, slow diffusion of an allele across a reproductive (either geographical or ethnic) barrier
-occurs due to migration