# LIFESCI 4 Lecture Notes - Lecture 18: Allele Frequency, Zygosity, Blue Arrow

LIFESCI 4 - Lecture 18 - Homozygosity by Descent

Clicker 1:

In a particular population the allele frequency of the ABO blood type alleles are as follows:

is 31%, I is 60%, and i is 9%IA B

If mating is random and the population is in Hardy-Weinberg equilibrium, approximately what

percent of the population will have blood type B?

A) 36%

B) 41%

C) 47%

D) 69%

E) None of the Above

Explanation:

- To get blood type B, an individual can either have genotype I or I iIB B B

- Allele frequency for .6 and i 0.09IB= 0 =

- Let’s define allele as (p), as (q), and as (r)IAIB i

- P[B phenotype] = p[ ] + p[ ] = = (0.6)(0.6) + 2 (0.6)(0.09) = 0.47IIB B iIB 2qrq2+

Clicker 2:

Which statement describes the swallow with the greatest evolutionary fitness?

A) A swallow that lives to be 3 years old and has four offsprings, two of which survive to

reproduce themselves

B) A swallow that live to be 5 years old and has five offsprings, one of which survive to

reproduce

C) A swallow that live to be 2 years old and has four offsprings, all of which survive to

reproduce

D) A swallow that live to be 7 years old and has three offsprings, all of which survive to

reproduce

E) All are equally fit

Explanation:

- Although the swallow lives only to 2 years, it has the highest number of offspring which

will continue to pass down the swallow’s genes

Clicker 3:

Within a certain population (that is in Hardy-Weinberg equilibrium) the frequency of the L allele

of the LM blood group is 0.2 and the frequency of the M allele is 0.8. This population has just

been infected with a virus that kills everyone with blood type M, but individuals with blood type

LM or L are unaffected by the virus. What is the allele frequency of L and M in the population

after the viral infection.

The allele frequency of L is:

A) ⅓

B) 4/9

C) 5/9

D) ⅔

E) None of the above

Explanation

- The genotype frequency can be predicted before the infection

since it was in

Hardy-Weinberg equilibrium

- We are given that L = p = 0.2

and M = q = 0.8

- Frequency of LL = = 0.04p2

- Frequency of LM = = 0.32pq2

- Frequency of MM = = 0.64q2

- Where 0.04 + 0.32 + 0.64 = 1

- After the viral infection, there is no more equilibrium since selection is involved

- M does not survive

- Frequency of LL remains unchanged = 0.04

- Frequency of LM remains unchanged = 0.32

- Frequency of MM = 0 since they all die

- Calculate frequency of L after the infection (p’) = = 5/9

0.04 + 0.32

0.04 + 0.32/2

- The new frequency (p’) was found by adding the proportion of (p) alleles

post-infection and dividing it by the total

- Dividing by total is necessary since after the infection, the frequency of LL

and LM are no longer percentages (does not add up to 1) → the

percentage needs to be recalculated

## Document Summary

Lifesci 4 - lecture 18 - homozygosity by descent. In a particular population the allele frequency of the abo blood type alleles are as follows: If mating is random and the population is in hardy-weinberg equilibrium, approximately what percent of the population will have blood type b? is 60%, and i is 9% B is 31%, i: 36, 41, 47, 69, none of the above. To get blood type b, an individual can either have genotype. Although the swallow lives only to 2 years, it has the highest number of offspring which will continue to pass down the swallow"s genes. Within a certain population (that is in hardy-weinberg equilibrium) the frequency of the l allele of the lm blood group is 0. 2 and the frequency of the m allele is 0. 8. This population has just been infected with a virus that kills everyone with blood type m, but individuals with blood type. Lm or l are unaffected by the virus.