(UFMG 2000)HOW ARE YOUR GENES?1 Some 200,000 babie

(UFMG 2000)

HOW ARE YOUR GENES?

1      Some 200,000 babies are born in the United States each year with deformed bodies, impaired minds and possibly fatal abnormalities in body chemistry - often because of defective genes or chromosomes. If a way could be found to "test" routinely the genes of prospective married couples - much as the couples now take Wassermann tests to detect syphilis - the toll might be reduced drastically. This is the goal of genetic counseling. And while it is still far off - testing is expensive and elaborate - genetic counseling centers in hospitals and clinics across the United States are already helping parents. Such centers help the parents of a defective child in their decision whether or not to have more children, and they advise couples with family histories of genetic diseases even before marriage.
2     The genes that help determine a person's individual characteristics - from the color of his eyes to the score he makes on an IQ test - are located on chromosomes within the cells of his body. Half of a person's chromosomes come from his father, half from his mother. Many diseases are the result of a single defective gene on one of the chromosomes. Achondroplastic dwarfism, for example, is caused by a dominant gene and any child who inherits it will have the disease. A genetic counselor confronted by a parent with such a disease could warn that half of his children risk the disease. More often, genetic diseases are caused by recessive genes. The most common is cystic fibrosis, a disorder that affects at least one in every 1,600 babies and causes their lungs and other body organs to become congested with mucus. A child who inherits only one of these recessive genes will not have the disease, but will be a carrier. If both parents are carriers, one in four of (2) their children will have cystic fibrosis, two will be carriers, and one will be normal.
3      Some diseases, (1) such as the blood clotting disorder, hemophilia, are sex-linked recessive defects carried on the female X chromosome. These genes generally produce disease only in male children when the X chromosome bearing the (3) faulty gene pairs with the father's Y chromosome. Half the sons of a female hemophilia carrier risk the disease; half the daughters may be carriers.
4     Until recently, much of genetic counseling has relied on estimates based on the law of averages. But researchers have begun to develop lab tests for carriers. There are blood, urine and other tests which show promise in detecting more than 100 genetic diseases, including cystic fibrosis, phenylketonuria (PKU), hemophilia and some forms of muscular dystrophy. As a result, a genetic counselor can tell the sister of a man with hemophilia with reasonable certainty whether she is a carrier.
5    Researchers are also detecting genetic defects even before a child is born. By amniocentesis, a process in which a needle is inserted through the mother's abdomen and into her uterus, researchers can withdraw samples of the fluid surrounding the fetus. By growing these fetal cells in tissue culture, researchers can detect chromosome defects or chemical abnormalities. "Intra-uterine 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."

HIRASAWA, L. & MARKSTEIN, L. Developing reading skills. Rowley, Massachusetts: Newbury House Publishers, 1978. p. 76-79. (Adapted text)

According to the text, it is INCORRECT to state that today genetic counseling is: