Question

A man and a woman affected with Babomania mate and have an unaffected daughter. Which of the following mechanisms of inheritance can be ruled out?

Choose all that can be ruled out.

Autosomal Recessive

Autosomal Dominant

Answer 1

Answer- Autosomal recessive

Considering, 'A' is dominant allele and 'a' is recessive allele

Lets take 2 cases :

Case 1: Disease is autosomal recessive

This means that genotype of both the parents will be 'aa'. And the cross between 'aa' genotypes will produce progeny with only 'aa' I.e. diseased phenotype. Refer punnette's cross below:

	a	a
a	aa	aa
a	aa	aa

Case 2: Disease is autosomal dominant

Genotype of parent 1: AA or Aa

Genotype of parent 2: Aa or AA

Now, since the progeny is disease free that means the genotype has to be 'aa'. Now from the above possibilities it can be seen that it is possible with only 1 genotype combination of both parents: Aa X Aa. Only this type of cross will produce 'aa' genotype I.e. normal phenotype. Refer punnette's cross below:

	A	a
A	AA	Aa
a	Aa	aa

So concluding it, the progeny being disease free but both parents showing disease is only possible when the disease is autosomal dominant. Thus we can rule out autosomal recessive possibility.