The following pedigree depicts a family with congenital deaf

The following pedigree depicts a family with congenital deafness. Considering generations l-lll only, is the mode of inheritance dominant or recessive? What information led you to this conclusion?

Solution

a) The mode of inheritance is dominant, as we can see that in the 1st generation the 3 and 4 being deaf carries it over to the 2nd generation and also on to the 3rd generation and hence it is a case of dominance in the genetic alleles. It can also be that the 10 and 11 of the 2nd generation being dominant gave rise to a dominant genetic third generation.

b) the possible reason for the 4th and 5th generation not having deafness is that the 9 and 7 of the third generation might be recessive and also there is a visible decrease in population. We can also note that the relationship between the 7 and 9 of 4th generation is really distant and hence they start lacking the allele for congenital deafness.