What is the?
The was originally described for plants. The avénement of human genetics has shown that cases of chimeras are possible in humans and could happen in the case of of dizygote pregnancy, i. e for fake twins. True twins, so called monozygotic, have the same genetic heritage.
This phenomenon is much more common as a result of the use of assisted procreation without the reason being known.
The is linked to an early anomaly, probably when the embryos of a twin dizygote pregnancy are only at the stage of a few cells. The disorder twins are from a double fertilization, which should have led to the birth of two newborn babies.
In rare ways, the two eggs fusion and the development of a single embryos normally continues while keeping two different genetic heritage between cells depending on whether they are from one or the other of the eggs.
The fetus thus have some parts of the body with a given genotypes and the rest is similar to that of a close relative.
Another cause is possible
In some cases, anomalies in the division of embryos may lead to different genetic heritage within the same individual. To understand, we must return to the original pattern of prenatal development.
When a child is designed, its genomes, that is all alleles and genes that they will possess, are formed from a cell of the mother (the embryos) and another his father (the sperm) from meiosis. The fusion of these two elements will allow him to have 46 pairs of chromosomes in each of his cells.
During the development of the fetus, cells split by two, then by four, etc. This is called mitosis. In each of these divisions, there may be “errors”. Suddenly, a cell can be found with not 46 chromosomes, but 45 or 47. If there are too many, the cell dies , but if there’s less, it’s not automatic. This is what happens, for example, in individuals - often female - with Turner syndrome (45, X0) for some cells and normal for others (46, XX).
Sometimes the damage can be more limited to a part of a chromosome or even a genes, and it’s kinda like one of the genes lost in battle.
The consequences of the of
The anomalies are mainly seen in the placenta or sexual organs. But in reality, it can only reach certain organs of the human body or only some cells.
The may also affect other cells, especially those in the bone marrow, the cells including red blood cells that determine the blood type.
The individual will therefore have cells that may have different characteristics and in particular express different proteins or antigens, such as those in the blood type.
If this man does not have the same blood type as his son (man is A and his son is AB), it is definitely related to the fact that having two different genetic heritage, he has blood cells in group A but that his sperm, which carries another type B.
1 or 2 cases out of 6.000 individuals
The cases are often shown in of, a pre-pregnancy diagnosis where the amniotic fluid is taken from the fetus. It is then discovered that there are two types of cells with a different genetic heritage.
It is important not to confuse the with more frequently in vitro culture anomalies that are linked to the artificial culture of cells in the lab.
The cases are very rare. Out of 6.000 births per year in our motherhood, we only observe about 1 or 2 cases of chimerism. The cases of chimerism from twins found in adults are even more rare, although their actual frequencies are in fact unknown.
The can turn out many years later. It can be discovered during a fertility check, in case of blood type determination, or when an internal transplant is done.
The presents no danger
In any case, the does not represent any danger to the individual. It has very little influence on other organs and therefore rarely identified.
It is even likely that the cases are more common than we think.