[单项选择] Defective Genes and Human Health Each of us carries about half a dozen defective(有缺点的) genes. We remain blissfully(快乐地) unaware of this fact unless we, or one of our close relatives, are amongst the many millions who suffer from a genetic disease. About one in ten people has, or will develop at some later stage, an inherited(遗传的)genetic disorder, and approximately 2,800 specific conditions are known to be caused by defects (mutations) in just one of the patient’’s genes. Some single gene disorders are quite common-—cystic(胞状的) fibrosis (纤维化) is found in one out of every 2,500 babies born in the Western World—and in total, diseases that can be traced to single gene defects account for about 5% of all admissions to children’’s hospitals. Most of us do not suffer any harmful effects from our defective genes because we carry two copies of nearly all genes, one derived from our mother and the other from our father. The only exceptions to this rule are the g
A. half of the children will be affected by the dominant genetic diseases
B. about 50% children of the parents with the dominant genetic diseases can be affected
C. when a child becomes an adult, a dominant genetic disease will become apparent
D. a normal gene will carry out all the tasks assigned to it and its counterpart, when the latter is dominant