Question

Explain why women show no disease symptoms can pass on some heritable diseases to their sons, who have symptoms. Their daughter are asymptomatic.

Answer 1

There are some genetic disorders which affect males mostly than females. These disorders are categorized as X linked recessive disorders. X -linked disorders include haemophilia, red green colour blindness, Lesch- Nyhan syndrome, Hunter syndrome. Recessive disorders are those disorders where mutation in both allele copies produce the disorder but in case of X linked disorders males are affected when mutation occurs in their X chromosome because males are hemizygous for X linked triats therefore these triats are expressed in males.

For females to show such disorders both of their X chromosomes should be mutated because females are homozygous for X linked triats. If only one of the X chromosome in female carries the mutant allele and other X chromosome carries normal allele, it wont produce disorder in female and female will have normal phenotype because females have two X chromosmes and both of their X chromosomes must be having mutant allele to have X linked disorder and such instances are rare when female carries two mutant allele. However such females (with one mutant and one normal allele on X chromosomes) are carriers and they can transmit the trust to their sons.