Chapter 17, Problem 40A

Summary Introduction

To describe:

The inheritance of hemophilia.

Introduction:

During reproduction, the offspring receives two set of genes from both paternal and maternal side. Sometimes due to some mutation, the genes carrying the sex-chromosome fail to express it properly, resulting in disease that are referred to as sex- linked diseases. Changes can occur in any one of the chromosomes.

Explanation of Solution

Hemophilia is a rare inherited bleeding disorder in which the blood does not clot properly. It is because that blood lacks sufficient blood clotting proteins or factors.

The gene associated with this disease is located on the X chromosomes and is inherited in an X-linked recessive pattern. If the gene carrying the disease is not masked by a dominant gene, the person is said to be hemophilic. Whereas, when there is another dominant gene masks the expressions of the recessive disease carrying person, the individual is said to be a carrier.

Generally, the expression of the X-linked recessive genes of hemophilia occurs more often in men than in women because men have a single X and Y chromosomes. But, women have two X chromosomes, so, the dominant gene suppresses the expression of faulty recessive gene and are carriers. Female as carrier pass on the genes to the next generations.

The genetic alterations which is responsible for causing hemophilia is passed down from parent to child through generations. Male will hemophilia pass the genetic disorder onto their daughter and not to their sons. Female carry the altered gene and pass on to their sons and daughters. Sons will be hemophilic while daughters carry the gene, only without any symptoms.