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.
