In humans, several hundred genetic diseases and disorders follow the dominant-recessive pattern. If a child inherits one dominant allele and one recessive allele he or she typically does not have the disease. A carrier can pass either the dominant or recessive allele to their child. It can receive a mutated allele from the mother and a normal allele from the father, or a normal allele from the mother and a mutated allele from the father. The child develops the disease only if he or she receives a mutated allele from each parent. When both parents are carriers, there is a 25 percent chance that a child will not have the disease, a 25 percent chance that it will have the disease, and a ...view middle of the document...
Because of this, many victims are unaware that they are color-blind. Several types of tests have been prepared for the quick diagnosis of color blindness and of the particular variations of the condition.Cystic Fibrosis, incurable hereditary disorder that causes the body to secrete an abnormally thick, sticky mucus that hangs on to the pancreas and the lungs, leading to problems with breathing and digestion, infection, and ultimately, death. Three decades ago most babies born with cystic fibrosis died in early childhood, but advances in diagnosing and treating the disease have significantly improved. Today more than 60 percent of babies born with cystic fibrosis reach adulthood.One of the most common fatal genetic disorders in the United States, cystic fibrosis occurs in about one in every 3,900 babies. About 1,000 new cases are diagnosed each year, usually before a child reaches three years of age. Approximately 30,000 American children and young adults have cystic fibrosis. The disease affects white people more often than black people: One in every 3,300 white babies is born with cystic fibrosis, but only one in every 15,300 black babies is born with the disease.Cystic fibrosis is caused by a defect in the gene responsible for manufacturing cystic fibrosis transmembrane conductance regulator (CFTR), a protein that controls the flow of chloride ions into and out of certain cells. In healthy people, CFTR forms a channel in the plasma membrane through which chloride ions enter and leave the cells lining the lungs, pancreas, sweat glands, and small intestine. In people with cystic fibrosis, malfunctioning (or absent) CFTR prevents chloride from entering or leaving cells, resulting in production of a thick, sticky mucus that clogs ducts or tubes in these organs. In the lungs, this mucus blocks airways and obstructs natural infection-fighting mechanisms, eventually turning the body's immune system against its own lung tissue. Similar blockage prevents crucial digestive enzymes produced in the pancreas from reaching the intestines, impairing the ability to break down certain foods. In healthy people most of the chloride in sweat is reabsorbed, but in people with cystic fibrosis, sweat glands cannot take up chloride ions, enabling excessive amounts of salt to escape in the sweat.Cystic fibrosis is an autosomal recessive genetic disorder. This means that to have the disease, a child must inherit two alleles of the defective gene, one from each parent. Many people carry a single cystic fibrosis gene, although they do not experience any significant health problems as a result; in the general population, approximately 1 in 31 Americans carries the gene. The disease can only occur in babies with two carrier parents. When both parents are carriers, they have a 25 percent chance with every pregnancy of passing two copies of the defective gene to their child.Researchers identified the gene responsible for cystic fibrosis in 1989. Since that time more than...
