Researchers come to different conclusions

Twins are not nearly alike that scientists think

Research attaches importance to monozygotic twins, as they are thought to have similar genetic makeup.

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A study published yesterday showed that the genetic differences between monozygotic twins, who are often called identical twins, can appear very early in embryonic development, a finding that prompts a review of how researchers know through twins what is innate. What is gained.

The birth of monozygotic twins, sometimes called identical twins, occurs when the ovum (or zygote) resulting from fertilization separates into two, thereby forming two fetuses.

Monozygotic twins are given great importance in research.

It is generally believed that they have a similar genetic makeup, and that their physical or behavioral differences are learned from the environment around them.

A study prepared by Icelandic researchers, and published in the journal Nature Genetics, focused on studying the mutations that occur at an early stage of embryonic development, and concluded that each monozygotic twin has an average of 5.2 different mutations from the genome of his twin.

The study authors noted that 15% of them had many of these various early mutations.

The researchers considered that these results indicate that previous studies have underestimated the role of genetic factors in the differences between monozygotic twins.

"The traditional model was based on using identical twins to help distinguish between the influence of genetics and the effect of the environment in analyzing diseases," said Carrie Stefanson, head of the Icelandic company Decod Genetics of the American pharmaceutical group Amgen.

And if identical twins who grew up separately were studied, and one of them developed autism disorders, the traditional explanation would be that the cause of these disorders was the environment.

However, this conclusion is extremely dangerous, according to Stefanson.

Because there is a possibility that the disease is the result of an early genetic mutation that occurred to one of the twins, but not to the other.

Stefanson's research team sequenced the whole genomes of 387 monozygous pairs of twins, along with their parents, spouses and children, to detect the genetic mutations.

It turns out that any mutation that occurs in the first weeks of fetal development is likely to include all the individual cells (ie, physical cells, such as those in muscles, organs, etc., but also reproductive cells or gametes), and to be transmitted to his offspring.

The researchers discovered in one of the pairs of twins included in the study a mutation in all the cells of one of the twins, which means that a mutation occurred at an early stage of development, but this mutation did not happen at all in his twin.

"One of the twins is the product of cell divisions in which the metamorphosis occurred (within the group of cells resulting from the first divisions of the egg), and only in this cell," while the other twin was formed from the other cells, Stefanson explained.

"These changes are interesting, because they allow exploring the way in which a twin pregnancy occurs," he said.

The

discovery prompts a review of how researchers know, through twins, what is innate and what is acquired.

The research team performed complete genome sequences of 387 pairs of monozygotic twins

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