Having two normal genes is a health protection2010-10-23
People who have used computers know, it is important to have a backup file, otherwise the computer virus trouble.
This approach tells us that, to ensure the stable operation of a complex system, there should be two management files.
Nature also has such a law, such as we have two eyes, two ears, two hands, and so on. Here you may wish to think about, "Why is the second, rather than three or four." The correct answer of course is two than three, four, has advantages.
Genes in human cells we also have two, one from the father and one from the mother. The presence of two genes means that even if one were destroyed, as long as another intact able to work, to ensure the healthy operation of the human body. If a person inherits two copies of the gene have damaged their parents, then this person is either aborted or a person born with defects.
If only one defective at the time of succession and the other a normal, then since cosmic rays, mutagenic substances in food and other reasons which led to another gene have also damaged two genes are not working properly, then the operation of cells there will be a serious obstacle, leading to severe illness, which inherited a defective gene is characterized by people who will be in relatively young age of onset, and have a family genetic predisposition.