Genetic variations in populations

Question 1

Mutation

Answer 1

One mutation per 30 million bps per generation
Average of one protein-coding gene per generation
Persistence depends on type of mutation (dominant, recessive, X linked) and selection (positive, neutral, negative)

Question 2

Deleterious mutations

Answer 2

Dominant lethal mutations last a single generation
Dominant conditions that affect reproductive success last one to a few generations
Late onset dominant (Huntington’s) last many generations
1/3 of X-linked lethal mutations lost per generation
Autosomal recessive mutations last many generations but eventually lost

Question 3

Founder effect

Answer 3

Genetic drift
Reduces variability and increases prevalence of rare mutations
Tay-sachs disease in european jews and french canadians

Question 4

Heritability

Answer 4

How much of the observed variation in a trait is caused by genetics (is difference due to genetics or environmental factors)

Highly penetrant, single gene disorders have heritability of 0, but in reality there is always variability (modifier genes and environment)

Question 5

Lambda S

Answer 5

Relative risk of disease given that a sibling is affected

Question 6

Drug sensitivity

Answer 6

Warfarin response has genetic variants in metabolising gene CytP450 and target gene VKOR

Low CYP2C9 activity and variations in VKOR can lead to excessive bleeding

Question 7

Heterozygote advantage

Answer 7

Heterozygous genotype provides advantages over homozygous (sickle cell)

Affects allele frequency over time

Question 8

Twin and adoption studies

Answer 8

Twin studies see how often a co-twin is affected if the other is. A higher concordance indicates a genetic cause

Adoption studies separate effects of genes and environment

Used to estimated heritability

Question 9

Assumptions of Hardy-Weinberg

Answer 9

Mating is random (but humans mate assortively)
No inbreeding
Allele frequencies remain the same over generations (Mutation, heterozygote advantage, genetic drift)