Chapter 23, Problem 19STP

Summary Introduction

To write:

If a couple with distance family members having cystic fibrosis give birth to a child with cystic fibrosis.

Introduction:

Genetic disorders are inherited disorders caused by mutations in one or more genes. The disorders can be either dominant, recessive, sex linked or chromosomal. Cystic fibrosis is one of the most common recessive genetic disorders. It is caused by a defect in the gene that codes for a membrane protein. Cystic fibrosis affects the mucus producing glands, sweat glands and digestive enzymes. Chloride ions are not absorbed into the cells but excreted in the sweat. Water does not diffuse from cells without sufficient chloride ions. It causes excessive mucus production, interrupts digestion and blocks the respiratory pathways.

Explanation of Solution

A person who is heterozygous for a recessive disorder is known as a carrier. If both the parents do not have the disease, they can be normal or may be carriers in heterozygous conditions. As their family members have cystic fibrosis, they can both be carriers of the disorder. When both parents are carriers of the same recessive disease, there is a 25% chance that the child will inherit the trait from both parents and have the disease, a 50% chance that the child will inherit the trait from only one parent and be a carrier, or a 25% chance that the child will not inherit the trait from either parent and will not be a carrier or have the disease.

Conclusion

When parents are carriers of the disease, the child may either inherit the disease, be a carrier or not have the disease.