Question

Why is sex-linked inheritance an example of non-Mendelian inheritance?

Answer 1

Mendelian pattern of inheritance is the classical mode of inheritance which follows the three postulates by Mendel, i.e. presence of two alleles, segregation of traits and independent assortment of genes.

However, these postulates as well as Mendel's pattern of inheritance do not hold true for sex-linked genes. The reasons for this observation are:

1. The segregation alleles is not possible during sex-linked inheritance since the male and female counterparts do not carry similar genotype.
2. These genes do not assort independently and hence a gene, or group thereof, is inherited with the chromosome always whenever a gamete is formed and fertilization takes place.

For example, color-blindness is an X-linked recessively inherited trait in humans which is sex-linked in nature. Hence, it does not follow the normal Mendelian pattern of inheritance as usual genes.