Congenital deafness (ar has many causes) A deaf-mute couple gave birth to a normal boy after marriage. Please explain and estimate the risk of recurrence from a genetic point of view.

Marriage between congenital deaf-mutes is forbidden.

Congenital deafness's disease is a common recessive genetic disease. Among a pair of pathogenic genes of this disease, one is inherited by the father and the other is inherited by the mother. Congenital deaf patients all carry a pair of pathogenic genes. If they get married, their children are likely to be born deaf. Therefore, congenital deaf-mute patients should not marry congenital deaf-mute patients.

First of all, deaf-mute can be divided into congenital deaf-mute and acquired deaf-mute. Acquired deafness is caused by various external factors such as infectious diseases and drugs after the baby is born, and it will not be inherited. Congenital deafness is not necessarily inherited: pregnant women are not fully differentiated in the early pregnancy, and if they encounter harmful substances, such as mother being infected with virus, being exposed to X-rays, being exposed to or taking some teratogenic substances or drugs, they may all cause "congenital" deafness. This deafness is not inherited (unless there is another recessive deaf-mute gene).

Hereditary congenital deafness can be divided into several situations:

Autosomal dominant inheritance of 1.

If one of the parents is sick and the sick one is heterozygote, the probability of the child's illness is1/2; The sick side is homozygous, and the children 100% are sick; If both parents are deaf-mute heterozygotes, then the probability of the child getting sick is 3/4, and 1/4 is normal. But if the child does not get sick, the offspring of the child will not get sick again, so there is no pathogenic gene in the child.

2 autosomal recessive inheritance.

Assuming that both parents have normal phenotypes, but both parents carry deaf-mute pathogenic genes and pass them on to the next generation, then a deaf-mute child will be born with a probability of1/4; However, if only one party passes the deaf-mute gene to the next generation, the offspring will become deaf-mute gene carriers and will not cause disease, with a probability of1/2; If the pathogenic gene is not passed down, the offspring without the pathogenic gene are healthy, and the probability is 1/4.

If both parents are born deaf and dumb, and they are alleles, then the child born is deaf and dumb, regardless of gender. Childbearing is not allowed in this case.

If one of the parents is born deaf-mute, then the children born are normal children (but deaf-mute gene carriers), calculated according to the genetic law.

If one parent is a deaf-mute gene carrier, the child will not get sick, but there is a 1/2 chance of becoming a deaf-mute gene carrier, and there is a 1/2 chance of becoming a normal person without deaf-mute gene.

In fact, children are less sick than the theoretical value. For example, deaf-mute patients often marry deaf-mute people because it is difficult to find a partner. If most of them are estimated by autosomal recessive inheritance, their children should all be deaf-mute, but the actual survey results show that about 70% of their children are not sick. This is because most parents carry non-allelic recessive genes, so there is a phenomenon of double heterozygosity without getting sick.

3 X linked (sex chromosome linked) inheritors and polygenic inheritance.

X-linked inheritance is rare (less than 2%), and it is generally female inheritance (unless it is homozygous). When men get sick, there are fewer homozygotes in women, and their sons are bound to get sick. Since the information provided by the counselor shows that his mother is deaf and his brother is normal, then X-linked inheritance can be ruled out. As for polygenic inheritance, it cannot be simply analyzed. Generally speaking, as long as both sides are normal, future generations should also be normal.

The disease may not be inherited, but it may be fetal development.

Only when the fertilized eggs produced by the combination of sperm cells and egg cells without pathogenic genes develop into new offspring will the offspring be normal.

If a deaf-mute couple gives birth to a normal child, it proves that the fetus is developing normally, so there will be no deaf-mute people.

In recessive genetic diseases, congenital deafness is controlled by a pair of alleles. Under normal circumstances, the probability of producing normal offspring is 3/4, and if it is a normal boy, it is 3/8.

So if there is no accident, the possibility of recurrence is very small.