The genes that help determine a person's individual characteristics—from the color of his
Many genetic defects, such as the hemophilia of European royalty, can be traced back through the family tree. And a genetic counselor can calculate probable risks for couples even before they have defective children. But faulty genes may also occur without warning by mutation in any generation.
In recent years, researchers have detected a number of disorders caused by an extra chromosome, or lack of part of a chromosome. Mongolism, a form. of retardation accompanied by short stature, a flattened nose and broad hands and feet, is caused by an extra chromosome. The parents of such a child have little increased risk of having another Mongoloid.
There are blood, urine and other tests which show promise in detecting more than 100 genetic diseases, including cystic fibrosis, hemophilia and some forms of muscular dystrophy.
Researchers are also detecting genetic defects even before a child is born. "Intrauterine detection," notes Dr. Henry L. Nadler of Northwestern University Medical School, "brings a new dimension to genetic counseling. The physician may now inform. the parents that they will have either an affected or a normal child. "
The original title of the passage can be best replaced by______.
A.Genes and Diseases
B.Genes and One's Characteristics
C.Genetic Defects and the Family Tree
D.Dominant and Recessive Genes