Genetics and inheritance: Albinism is a trait found in many species which reduces or eliminates pigmentation in the skin, hair, and eyes. Albinism is inherited as a recessive trait (only those with aa – homozygous recessive) will show the features of Albinism. (provide percentages and show your work)
a. if two heterozygous individuals reproduce, what are the chances they will have an albino child?
b. if one of their children is homozygous recessive, and grows up to marry and have children with another albino, what are the chances they can have a child who is NOT albino?
c. Imagine a community where people discriminate against albino individuals, and force them to move into their own village, and only marry one another. Would this be a sure way to eliminate albinism in the entire community? (think about both villages) Why or why not?
d. Continuing with the imaginary community above, what do you think would happen to the total number of albino individuals in the population (both villages)? Would it increase, or decrease? Explain.
e. Which of the four evolutionary forces is at work here? Could there be more than one? Explain.
The correct answer and explanation is:
a. Chance of an albino child from two heterozygous individuals (Aa x Aa):
To solve this, we use a Punnett square. The parents are both heterozygous, so their genotypes are Aa.
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
- AA (homozygous dominant): Not albino.
- Aa (heterozygous): Not albino, but a carrier.
- aa (homozygous recessive): Albino.
Out of the 4 possible combinations:
- 1 AA (not albino)
- 2 Aa (not albino, carriers)
- 1 aa (albino)
So, 1 in 4 or 25% chance of having an albino child.
b. If a homozygous recessive child (aa) marries another albino (aa), what are the chances of them having a child who is NOT albino?
If both parents are aa, all of their children will inherit one a allele from each parent, making them aa (albino). There is 0% chance that their child will not be albino.
c. Could forcing albinos to marry only each other eliminate albinism from the entire community?
No, this would not eliminate albinism from the community. Since albinism is inherited as a recessive trait, carriers (Aa) can still pass on the a allele, even if they do not show the albino phenotype. Forcing albinos to marry only one another would likely increase the frequency of aa homozygotes, because all their offspring would be albino (aa). In the general community, the Aa carriers would still carry the recessive allele, meaning albinism could reappear in future generations if carriers interbreed.
d. What would happen to the number of albino individuals if the albinos marry only one another?
If albino individuals (aa) are isolated and only marry other albinos, all of their children will be albino (aa). As a result, the number of albino individuals in the population would likely increase over time, because there would be no genetic mixing to introduce the dominant normal (A) allele. This would lead to an increase in the frequency of the aa genotype in the isolated group.
e. Which evolutionary force is at work here? Could there be more than one?
The evolutionary force at work is genetic drift, which refers to changes in allele frequencies due to random chance. In small populations, such as the isolated albino group, genetic drift can lead to the increase or decrease of certain traits, regardless of their fitness. Additionally, inbreeding could also be occurring, as individuals with similar genetic backgrounds are mating with one another, which increases the likelihood of homozygous recessive traits like albinism. Both genetic drift and inbreeding could influence the population dynamics of albinism in this scenario.