Lecture 5

Question 1

What is the definition of a gene?

Answer 1

A nucleotide sequence coding for, or regulating expression of, a phenotypic trait

Question 2

What is the significance of a gene?

Answer 2

Genes are the basic unit of heredity in a living organism and contain the data needed to pass genetic information to offspring

Question 3

What is the definition of an allele?

Answer 3

Alternative sequences of a gene at the same locus

Question 4

What is the significance of an allele?

Answer 4

The version of alleles present can determine heterozygosity vs homozygosity

Question 5

What is the definition of allele frequency?

Answer 5

The proportion of alleles of a given type

Question 6

What is the significance of allele frequency?

Answer 6

Allele frequency shoes the genetic diversity fo a species

Question 7

Equations for genotype frequencies:

Answer 7

P(XX) = P = # X / total # of alleles Q(Xx) = Q = # Q / total X of alleles R(xx) = R = # R / total 3 of alleles

Question 8

Equations for allele frequencies:

Answer 8

p(X) = p = P + Q/2 q(x) = q = R + Q/2

Question 9

What does Hardy-Weinberg assume?

Answer 9

Allele frequencies don’t change (no evolution) and that genotype frequencies can be predicted from allele frequencies

Question 10

What are the Hardy-Weinberg condition?

Answer 10

1. Random mating
2. Infinite population size
3. No gene flow
4. No mutation
5. No selection

Question 11

Hardy-Weinberg equation:

Answer 11

p² + 2pq + q² = 1

Question 12

What is the relationship between allele frequecies and genotype frequencies?

Answer 12

Question 13

What is the definition of heterozygous advantage?

Answer 13

The stabilization of allele frequencies at some intermediate (both alleles maintained in a population)

Question 14

Deducing frequencing from H-W ratios:

Answer 14

You can always deduce allele frequencies from genotype frequencies, but genotype frequencies can only be predicted from allele frequencies if we know that all 5 H-W conditions are true

Question 15

What happens when there is selection against a dominant allele?

Answer 15

1. Both AA and Aa are selected against (1 - s)
2. Dominant deleterious allele is purged from the population
3. a becomes fixed at frequency = 1

Question 16

What happens when there is selection against a recessive allele?

Answer 16

1. aa is selected against (1 - s)
2. Recessive deleterious allele persists for many generations (hard to eleminate bc present in Aa, which is as equally fit as AA)
3. Population is not fixed for A