Question

14). During the early 1700’s, a small group of pacifist Protestants fled Germany to avoid religious persecution. This group, the Dunkers, settled in the farmland of eastern Pennsylvania and has been relatively isolated from other groups of people living in the area (they have strict rules about marriage outside of the group). The original group was comprised of 50 families.
The current Dunker population is genetically distinct from the rest of the United States (and modern Germany) in terms of the ABO blood group system. In the Dunker population, the frequency of the I A allele is .30 (30%) and the frequency of the O blood type is .16 (16%). In the general US and German population the frequency of the I A allele is .40 and the frequency of the O blood type is .25 (25%).
a). What are the frequencies of the I B and i alleles in both populations? Show your work.
b). Use your knowledge of the founder effect to explain the differences in ABO blood group allele frequencies between the 2 populations and indicate whether or not this is an example of adaptive evolution.

Answer 1

a) In the Dunker population, the frequency of IB allele is 0.3 and the frequency of i allele is 0.4. In the general population, the frequency of IB allele is 0.1 and the frequency of i allele is 0.5.

If:
$I^{A}$ - the frequency of IA allele
$I^{B}$ - the frequency of IB allele
$i$ - the frequency of i allele

Then:
$I^{A} I^{A}$ + $I^{A} i $ - the frequency of individuals with A blood type
$I^{B} I^{B}$ + $I^{B} i $ - the frequency of individuals with B blood type
$ii$ - the frequency of individuals with O blood type

Let's first take a look on the Dunker population:
$I^{A} = 0.3$
$ii=0.16$

Since there is only one possible genotype for O individuals - ii - the frequency of the allele i is square root of the frequency of O individuals:
$i= \sqrt{ii}$
⇒ $i = \sqrt{0.16}$
⇒ $i=0.4$

Now, we have the frequencies of two alleles ($I^{A}$ and $i$). To calculate the frequency of $I^{B}$ allele, we will use the formula:
$I^{A} + I^{B} + i = 1$
⇒ $I^{B} = 1- I^{A} - i$
⇒ $I^{B} = 1-0.3-0.4$
⇒ $I^{B} = 0.3$

Now, in the general population:
$I^{A} = 0.4$
$ii=0.25$

Similarly to the work for the Dunker population:
$i= \sqrt{ii}$
⇒ $i = \sqrt{0.25}$
⇒ $i=0.5$

$I^{A} + I^{B} + i = 1$
⇒ $I^{B} = 1- I^{A} - i$
⇒ $I^{B} = 1-0.4-0.5$
⇒ $I^{B} = 0.1$



b) A founder effect is a result of geographical separation of a few individuals from the original population. Those founding individuals will form a new population. The Dunker population was not only geographically separated, but also genetically. The group interbreeding was present resulting in increasing those allele frequencies that were the most common in the founding population. In this case, the most individuals from the founding population had B blood type.