What Disorders Are Caused By Gene Defects and Chromosome Abnormalities?
Cystic Fibrosis Cystic fibrosis is the most common, lethal genetic disease in the USA. It strikes 1 in 2,500 persons of European descent, but is relatively rare in other groups. The gene involved in cystic fibrosis codes for a membrane protein that transports chloride ions into certain types of cells. The defective allele is autosomal recessive, and persons homozygous for this allele have too much chloride outside of their cells. In regions where mucus is present, the chloride causes it to become much thicker and stickier than normal. The lungs are greatly affected, since mucus clogs the airways and the lungs may become inflamed. If untreated, most children die before the age of 5. Since the cystic fibrosis allele is recessive, one or both parents can be carriers without showing any symptoms. That is, they are heterozygous for the gene. This diagram shows the possible genotypes and phenotypes of children from heterozygous parents. The numbers beneath each person represent chromosome 7,
