Genetic research Research: Identical twins leave an eternal mark on sibling genes, even if the other disappears before birth

When an embryo divides in two, a label remains in the genes. The discovery is a scientific breakthrough that will benefit scientists.

Man originates when the ovum fertilizes. In the womb, it first develops into a small embryo, a cell mass barely the size of a grain of sand.

Then the cells begin to divide and divide. They differentiate into different organs and tissues, the whole person.

The result is a person who, for example, reads this story.

Soon however, after fertilization, usually within the first two weeks, the embryo may split in two. Indeed, two individuals begin to grow in the womb, identical twins originating from the same ovum.

This division leaves a permanent trace inherited by man, now found for the first time in a recent study.

Anyone’s DNA can be used to see if they have identical siblings. Or has he ever had: even if the life of the sibling had already been extinguished in the womb, the memory of this unborn ghost twin appears in the inheritance of the surviving sibling.

An interesting result is reported Nature Communications in a scientific publication.

Identical the twins have been researched by shelf meter, but there are still many mysteries in the stages of the birth of the twin.

The formation of identical twins appears to be more or less constant throughout the world. About three in a thousand natural pregnancies produce identical twins. Thus, the genes of the parents hardly affect the division of the embryo.

“The emergence of identical twins is one of our few traits that is hardly affected by genes at all. Now, for the first time, we have found a biomarker that tells people about this, ”says the professor who led the research Dorret Boomsma From the Dutch twin register in the bulletin.

A study led by Vrije Universitet investigated the so-called epigenetic profile of a total of 6,000 twins.

Human the genome and traits are encoded in DNA and packaged into chromosomes in each cell.

But DNA is also overrun by so – called epigenomic genes, which have a kind of chemical label that regulates the function of genes.

These chemical patches live and change during human life, for example, under the influence of the environment. More specifically, there is talk of gene methylation.

Thus, such unique methylation changes were now found in the genome of identical twins at specific sites on the chromosome. The changes appear to be of the same type in all twins, and stem from something that has happened in the womb.

“Identical twins differed from others by more than 800 methylation sites,” says an academics researcher specializing in epigenetics Miina Ollikainen In a press release from the University of Helsinki.

Ollikainen was involved in the study along with a pioneer of twin research, a professor Jaakko Kaprion with. Of the subjects studied, 1,700 were Finns, as part of a twin cohort collected by Kaprio.

“The discovery can be described as a breakthrough, but so far it is a joy mainly for researchers.”

“When in the early stages of embryonic development, two developable embryos – two different people – are created. This event can now be viewed backwards from the present moment, “Kaprio tells Helsingin Sanomat.

Thus, it can be ascertained from anyone whether he has identical siblings, or whether he has ever been the other party to such an embedded embryo.

However, such tests are not now coming to stores, Kaprio points out.

The discovery can be described as a breakthrough, but so far it is a joy mainly for researchers who are trying to understand what is really going on in the early stages of individual development.

In the study the methylation changes characteristic of the twins were found mainly in the middle regions of the chromosomes, but changes were also observed at the ends of the chromosomes, i.e. telomeres.

The most interesting changes were found in areas related to cell division.

“It is in a given situation that two embryos are born instead of just one embryo continuing to grow. It is not known why this happens, but without that event there will be no identical twins, ”says Kaprio.

Methylation changes associated with cell division may be key to this mystery. Changes were seen in areas that seem to regulate how tightly the cells in the body are attached to each other. This could explain why the embryo splits in two.

“Unidentified twins also strongly reflect the conditions in society. “

Genes changes in methylation could also reveal why identical twins have certain types of fetal damage more often than others.

After two weeks of egg fertilization, the embryonic cells begin to differentiate and slowly produce precursors of various organs and tissues.

If the embryo divides only at this stage and succeeds in development, the end result will be grown together, i.e. the so-called Siamese twins.

Unidentified twins, on the other hand, are when two different eggs fertilize. Twins with inherited identities are ordinary siblings, that is, they share half of their genes.

Identical The birth of twins is not known to be affected by parental genes, but the tendency to have unidentified twins can pass through the family.

“Unidentified twins also strongly reflect the conditions in society. In a good nutritional situation, more non-identical twins are born, ”says Kaprio.

This can also be seen in the history of Finland, when the countryside has had bad harvests.

“There have been clearly more twins in places where the sea has provided a steady diet than inland.”

Read more: A twin brother impairs a girl’s chances of success in life

Read more: Twins live longer than the rest of the population – the twins have a friend through life as well as support and security


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