Question

Which observations in a pedigree indicate a probable autosomal dominant (AD) trait transmission

Answer 1

Hereunder i enclose the images :-

- the above two pedigree observations indicate a Dominant trait.

- the disease must be dominant if every child of affected children has affected parents.

- the unaffected mother in (II) generation , who is marrying in , doesn't carry an allele for the disease. So the affected child inherits an allele only from the affected father.

No child could be affected by a single autosomal recessive allele or x linked recessive allele, so the trait is dominant.

In the case 1 affected son (5) has an affected father (3) the disease must be AUTOSOMAL DOMINANT. A father does not transmit X-linked alleles to a son, so the disease cannot be X-linked dominant.

In case 2. When an affected daughter (5) has an affected father (3) , we cannot determine whether the DOMINANT disease is autosomal or X-linked.

The affected father can transmit either an autosomal dominant allele, or an X-linked dominant allele to his daughter.

So case 1 is a pedigree indicate a probable autosomal dominant trait transmission.

Hope you got your answer. Thanks.