Question

A genetically diseased father marries a normal female and gives birth to eight children. Out of them,three girls were carrier and five sons were normal. Which type of genetic disease is seen in the given case?

• A. Sex-influenced disease
• B. Blood group inheritance disease
• C. Autosomal disease
• D. Sex-linked disease

Answer 1

The correct option is D Sex-linked disease

From the pedigree chart that has been drawn, we can conclude that it is not a Y linked trait. Had it been one, the sons would have been affected and not the daughters. So, it is either an autosomal or X linked trait.
If it was an autosomal trait, sons and daughters would have had almost an equal probability of getting affected. But here we can see that only daughters are affected and all the sons are normal. So, this rules out the possibility of this being an autosomal trait. This is definitely an X linked trait.
Only the father is affected and the mother is unaffected. The daughters receive one X chromosome from each parent. Since the mother has normal alleles, she would pass on them to the daughters. The daughters would receive defective alleles from the father. Since daughters are carriers for the trait, it is a recessive one.
Hence, the above pedigree shows the transmission of an X-linked recessive trait.
It’s not a sex influenced trait. Sex influenced traits are mostly located on autosomes and are present in both the sexes, but their expression is to a different degree in each sex.
It’s not a blood group inheritance disease either. These are located on autosomes.