Question

Tay Sachs is an autosomal recessive disease's leading to nerve cell damage and early childhood death. 1 in 250 humans are carriers. There is NO BENEFIT to being a carrier for this disease. Since there is no benefit, list the hardy Weinberg assumptions in order of likely reasons that this disease is so widespread AND describe why you piked this order. (no more than 1-2 sentences each)

Answer 1

The Hardy Weinberg assumptions are basically rule that eliminate the 5 evolutionary forces. In this exercise you have to propose what evolutionary force might be leading to the maintainance of Tay Sachs alleles in the population. These are the assumptions and their respective evolutionary force:

- No mutation: Eliminates mutation

- Randome mating: Eliminates endogamy

- No gene flow: Eliminates migration

- Infinite population size: No genetic drift

- No selection: Eliminates natural selection

Natural selection is already discarded, because we are being told there is no benefit in being a carrier. Now, think that the homozygous is the problem (autosomal recessive trait), so any force that favors homozygosity is not going to help, then we can eliminate endogamy and genetic drift too.

We are left with gene flow and mutation. Gene flow favors allelic diversity, thus favors heterozygosity. Heterozygosity favors the maintainance of recessive traits, so this force is favoring the carrier maintainance. But mutation has a larger effect on this phenomenon, as the gene involved in the disease seems to have a lot of possible mutations that lead to the disease.

So the likely reasons that this disease is so widespread are:

1.- Mutation. (No mutation assumption)

2.- Gene flow. (No gene flow assumption)

3.- Genetic drift (Infinite population size assumption)

4.- Endogamy (Random mating assumption)

5.- Selection (No selection assumption)