Is Cousin Marriage Really Dangerous?

 Is Cousin Marriage Really Dangerous?

Is it really true that if first cousins ​​marry each other, their children are more likely to have genetic defects? If we have a basic knowledge of the science of genetics, the answer to this question becomes a little easier to understand

Historically, cousin marriages have been common in every part of the world - because in the past the means of transportation were so limited that meeting was limited to a few miles - that would mean When it comes to finding a mate, you often have people from your own family available - so it was common to marry first cousins ​​and second cousins.

If a man marries his fourth cousin (ie a man whose fourth generation - grandfather's grandfather) is common, they will have 0.2% DNA in common - if he marries a third cousin, he will have 0.78% DNA in common. If he marries a second cousin, he will have 3.13% DNA in common. And if he marries a first cousin, he will have 12.5% ​​DNA in common. It is said that children will have a genetic problem - sibling marriage is forbidden in every culture because doing so will involve 25% of DNA in common, which will greatly increase the chances of genetic disease in children.

Many people defend cousin marriage on the grounds that there is no genetic problem in their family, so cousin marriage in their family is not likely to cause genetic problems in children - but this argument is not correct - in children. It is not necessary for the parents to have any apparent genetic disease for the possibility of a genetic disease.

Cystic fibrosis, for example, is caused by a defect in the CFTR gene, but the disease only appears if both copies of that gene are mutated in one's DNA - if one has a mutated gene. If there is only one copy, the person does not have cystic fibrosis - but such persons will be considered carriers of the disease - if the carrier of the mutated CFTR is married to a person who does not have this mutation. Children have a zero chance of developing the disease - but if both spouses have the same mutation, then children have a 25 percent chance of developing the disease - a 25 percent chance of being infected by both parents. This mutated gene will be found and children will have cystic fibrosis

What is the probability of any disease in children from the marriage of the first cousin? This possibility arises when both spouses have mutated genes for the genetic disease but the spouses themselves do not have the disease. This calculation is not as simple as it may seem at first glance. If grandparents have all these genes, then the answer to this question will be different. If only grandparents are in grandparents, then the answer will be different. It can be said that according to the calculations of geneticists, the probability of a single genetic disease in children from the marriage of first cousins ​​is up to 7% while the probability of the same disease in the general population is up to 4%.

You might be wondering if there is a 4% chance of a genetic disease in the general population and a 7% chance of having the disease in children from a cousin's marriage, if there is only one genetic risk in humans. There would be thousands of genetic diseases whose mutated genes may be present in the DNA of our ancestors. First cousin marriage increases the chances of each of these genetic diseases. - Overall, first cousin marriages are more likely to have at least one genetic disease in children, and more likely to have genetic diseases in the general population.

If the parents of first cousins ​​who marry each other are also first cousins, then the risk of genetic diseases in children increases even more - if their grandparents were also first cousins ​​and grandparents were also first cousins, the risk would be even higher. This is because in this case new genetic material is not added to the family for many generations and new combinations of old genes are formed in which many combinations lead to genetic diseases.

The easiest way to avoid all of these problems is to avoid family marriages, especially the marriage of first cousins ​​altogether - if this is not possible then at least the genetic test of the couple must be done. Should be done to assess the possibility of relatively common genetic diseases such as thalassemia in children - if these genetic tests show the possibility of such common diseases, then the annulment of this marriage should be seriously considered. Keep in mind that genetic tests usually only provide information about a few diseases - so if the results of genetic tests are encouraging, there is still the possibility that some of the genetic diseases that have not been tested Diseases can occur in children.