Question

Polydactyly in man is due to
A. Autosomal recessive allele
B. Autosomal dominant allele
C. Sex linked recessive allele
D. Sex linked dominant allele

Answer 1

Hint: Polydactyly is not a multifactorial trait, it is associated with autosomal dominant mutations in single genes. Polydactyly, the term has “poly” which means many thus, it takes place due to mutation in a variety of genes.

Complete Answer:
- The term polydactyly comes from the Greek words “poly” which means many and dactylos means digits. It has many types but mainly it takes place when next to the fifth finger or toe extra digits grow. It is mainly caused due to genetic mutation and sometimes due to environment causes as well. It is a rare condition.
- The extra digit or digits that have been formed are sometimes complete and fully functional, in some cases that are partially formed with some bone, sometimes it is formed like a small mass of soft tissue known as nubbin. There is no phenotypic difference between homozygote and heterozygote.
- Same types of them were found in the same family suggesting that they are genotypically identical. The segregation distortion in favor of affected in the offspring of affected fathers could be interpreted as the effect of a sex-linked recessive modifier gene acting on an autosomal dominant polydactyly gene during gametogenesis.
- As it would be expressed in both conditions that is in homozygous or heterozygous condition so it has to be dominant and as it lies on autosomal chromosome

So the answer has to be B) Autosomal dominant allele.

Note: As inherited as an autosomal dominant entity with variable penetration caused by defects that occur in the anterior-posterior patterning of limb development. In humans at least 10 loci and six genes causing non-syndromic polydactyly have been identified.