Slide 1
Ok -
let's work through the solutions to these problems.
In this question, you are given the frequency of the dominant allele (p = .3) and the frequency of the recessive allele (q = .7).
You are asked to determine the frequency of carriers in this population.
Slide 2
Remember,
carriers are heterozygotes and to determine the frequency of heterozygotes you
always need to multiply by 2. Thus we see that in this population, the
frequency of carriers is .42 or 42%.
Slide 3
This question asks you
to determine an allele frequency when you are given a genotype frequency.
When you are presented with a Hardy-Weinberg question - I suggest you
take the time to figure out what information you have been given. In
this question you are told that 81% of the people in Smallville USA have a
smooth chin. Having a smooth chin is an expression of a person's
genotype - and having a smooth chin is the recessive condition. That
means that q^2 =81% or .81.
Slide 4
Remember, q^2 is the
frequency of homozygous recessive individuals in the population and anyone
with a smooth chin is homozygous recessive.
Slide 5
If q^2
equals .81, we can then solve for q by taking the square root of .81 - which
equals .9. If q = .9, then p=.1 or 10% (p is the frequency of the
dominant cleft chin allele.
So the answer is A - 10%.
Slide 6
Now
we will do some sample problems looking at a gene with three alleles - and we
will use the ABO blood group as our example. The ABO blood group gene
has three alleles - the A allele, the B allele, and the O allele. Given
these three alleles - what are the possible genotypes?
Slide 7
There
are 6 different possible genotypes - remember that in this gene the A and B
allele are both dominant to the O allele and A and B are codominant to each
other. So while there are 6 different genotypes there are only four
different phenotypes - type A blood, type B blood, type AB blood and type O
blood.
Slide 8
To apply this blood group gene to the
Hardy-Weinberg equation we can standardize the notations so that p, q, and r
are the A allele, B allele, and O allele respectively.
The genotype frequencies are p^2 + 2pq + q^2 + r^2 + 2pr + 2qr and they correlate to the blood group genotypes: IAIA + IAIB + IBIB + ii + IAi + IBi.
Slide
9
This question asks you to apply your understanding of the ABO blood group
to the Hardy-Weinberg variables.
Slide 10
The answer is E - Both A
and B. This is because p^2 refers to the homozygous A genotype and 2pr
refers to the heterozygous A and O genotype. Both genotypes result in
Type A blood.
Slide 11
So now we are ready to answer a question
about the frequency of the B allele in a population. We are told that in
this population, the frequency of the A allele is .3 and the frequency of
people with Type O blood is 36.
Slide 12
Again, it is helpful to
take the time to write out what is known about the population. We know
that the A allele is .3 - this is p. We also know that the frequency of
people with type O blood is .36 - this is the homozygous recessive genotype or
r^2.
From r^2 we can solve for r which equals .6.
Given these numbers, we can now determine that the frequency of the B allele is .1.
Slide 13
Now you are asked to determine the frequency
of people with Type B blood.
Slide 14
You can use the
calculations you did for the previous question and recognize that there are
two ways to have Type B blood - either genotype homozygous B which corresponds
to q^2 or heterozygous for B and O which corresponds to 2qr. In this
population, 13% of the people are expected to have Type B blood.