Question

3. [1 point] Prof. Small is bald. Prof. Fitch is bald. Assume that baldness is an autosomal recessive r assume that the professors are hermaphrodites and that you could cross them to distinguish whether their baldness is due to the same genetic locus (Hypothesis 1, H1) or due to different genes altogether (Hypothesis 2, H2). How would you distinguish between these two hypotheses (i.e. what genetics experiment would you do, and what would these hypotheses)? be the predicted results for

Answer 1

In order to answer this question, the most important thing one must understand that an autosomal reccessive trait shows its phenotype only in homozygous condition. Which means that both the professors must be homozygous for the gene/genes responsible for the baldness.

Now the case of Hypothesis 1, which states that the baldness is caused by a single gene which share the same locus in the autosomes of bothe professors, the genetic constitution or the genotype of both the professors must be 'pp' and 'pp' (here small letter 'p' is the allele responsible for baldness). Therefore as you can understand that both the professors will have thi allele 'p' in 100% of their games (as homozygous). Thus on mating between the two professors(as stated they are hermaphrodite) there is only one genotype formation possible which is 'pp', where each allele 'p' is contributed by the either professor. Therefore all the progenies will have the genotype 'pp' for the gene causing the baldness and therefore all the offspring will be bald, irrespective of the gender(as the trait is autosomal).

In case of Hypothesis 2, which states that the case for baldness in each professor is contributed by differnet genes, the genetic composition of the two professors will be 'pp' and 'qq' where 'pp' is the homozygous constitution of the prof. small and 'qq' is the genotype of prof. fitch. Now the important question, is there any allele 'p' in prof. fitch and is there any allele for gene 'q' in prof. small? The answer to this question is, yes there might be such alleles in both the indvidual(as differmet locus for each gene), but we must also remember that these alleles can be present in heterozygous or homozygous dominant condition which ultimately doesn't contribute to baldness. Therefore we will assume that the other alleles are not expressed properly. Now essentially this means that we will be crossing between the two genotypes which can be:

(i) Prof. small (ppQQ) X Prof. Fitch (PPqq)    OR (ii) Prof. small (ppQq) X Prof. Fitch (Ppqq)

Now in case (i) : All the progenies will have the genotype will be 'PpQq', which leads to none of the reccessive allele to be in homozygous condition. Therefore all the offsprings will be having normal hair (because homozygous condition causes baldness).

In case (ii) : The possible genotypes of the offsprings are: PpQq : ppQq : Ppqq and ppqq (found by punnet square crossing). Which essentially highlights that there is chance of 75% of an offspring to be bald as the genotype PpQq is the only one which one will be having normal hair.

Therefore now the final decision can be made as :

If all the offsprings are bald then Hypothesis 1 is correct. Otherwise if the offsprings have either result as case (i) or (ii) then we can conclude that hypothesis 2 is correct.