Question

Amazingly for rodents, some of these guinea pigs have enlarged canine teeth or ‘fangs’, and your former crush notes that more males have fangs than do females. S/he/they crosses true-breeding fanged males to true-breeding fanged females and produces a generation in which males have fangs but females to not.

Inbreeding the F1 produces piggies that have the following ratios:

Males: 3 fanged: 1 fangless

Females: 1 fanged: 3 fangless.

i. Is this trait sex-linked or autosomal?

j. If autosomal, how do you explain the fact that the phenotypic ratios differ by sex?

Answer 1

Please find the answers below:

Answer i: According to the information, the trait is more pronounced in males as compared to females as the ratio of fanged males is higher after a true-breed cross. Hence, it strongly suggests that the trait is sex-linked in nature.

Answer j: As the trait is sex-linked, it is highly expressed in females as compared to males. However, the fact that not all females are fangless and not all males have fangs make the observation that the trait is sex-affected, not sex-linked in nature. This means that the gene for fangs is located on the autosomes and inherited in a recessive manner. Further, presence of even a single dominant allele helps in expression of the allele. Thus, cumulative observations suggests that the trait is inherited in autosomal recessive manner and the expression is enhanced in a sex-affected manner.