Why some people have different natured genomes in their cells

Think of mermaids. They might look cute on beaches when you imagine a wonderful looking half woman and half fish. But in reality people don't like playing with genes in labs. You might even frown upon researchers who are trying to create chimeras using different natured genomes for various research purposes.

                                      Extreme Science: Dr. Krishna Kumari Challa's  Art work based on the theme

But if I tell you human chimeras already exist in nature, what will you say?

When an individual carries two or more genetically distinct cell lines in different parts of his/her body, the phenomenon is called  genetic chimerism. 

 Genetic chimeras may be quite common, disguised in perfectly normal bodies harbouring genetically distinct cell lineages but the individuals that have them may not even know that they are Chimeric! They only came to light when the phenotypes associated with the two distinct genomes were so discordant that the resulting individual was clearly exceptional, with patches of distinct skin coloration throughout the body, for example, or hermaphroditic genitals.

In 1976, researchers from the Lister Institute of Preventive Medicine in London published the puzzling case of a woman who had two different blood types: 93 percent of her red cells were type O, while the remaining 7 percent were type A1, the most common type A subgroup (1). A few years later, Winifred Watkins of the MRC Clinical Research Centre and colleagues came across another blood donor with two distinct red blood cell types, and further investigation led to an even more astonishing finding: a phenotypically normal man, with presumably XY cells in his testes and most of his body, was found to carry XX cells in his skin and other tissues (2).

A man who had the life-saving procedure (bone marrow transplant) as part of his treatment for acute myeloid leukaemia,  a type of blood cancer, has found out that that DNA of his blood changed to that of his donor (5). But following a swab test four years later, he was told that the DNA in his lips, tongue and cheeks had now altered too. What 's worse 's that all of the DNA in his semen now belonged to his donor.

How can chimerism occur? Our present knowledge tells us this can happen in four ways...

1. When a foetus absorbs its twin. This can occur with fraternal twins, if one embryo dies very early in pregnancy, and some of its cells are "absorbed" by the other twin. The remaining foetus will have two sets of cells, its own original set, plus the one from its twin.

Can  a baby have two biological fathers? Chimerism is the only way this could happen biologically. 

For one baby to have two fathers what would have to happen first is bipaternal twins, which is rare. It is when two eggs get fertilized by two different men's sperm and become fraternal twins. For a chimera to happen, then one of those twins would die early in the womb and the other twin would absorb it and then fuse together into one person (a chimera). 

2. When bone marrow transplantion takes place. Leukemia patients are treated with bone marrow transplantation. The person will have his own bone marrow destroyed and replaced with bone marrow from another person. Bone marrow contains stem cells that develop into red blood cells. This means that a person with a bone marrow transplant will have blood cells, for the rest of his life, that are genetically identical to those of the donor, and are not genetically the same as the other cells in his own body.

In some cases, all of the blood cells in a person who received a bone marrow transplant will match the DNA of his donor. But in other cases, the recipient may have a mix of both his own blood cells and donor ones, according to a review paper in the journal Bone Marrow Transplantation (3). 

3.  If you've had a blood transfusion, the cells from the original blood donor will briefly be present in your body. However, among traumatically injured patients who received blood transfusions, the donor’s cells have been detected even decades after the transfusion.

4. Pregnancy can make a woman a chimera. This happens in almost all pregnant women, at least temporarily. When a woman gets pregnant, a small number of cells from the foetus migrate into her blood and travel to different organs (microchimerism). Now don't get frightened.  This is a natural phenomenon, so you need not worry.

When some researchers tested tissue samples from the kidneys, livers, spleens, lungs, hearts, and brains of 26 women who tragically died while pregnant or within one month of giving birth, they found that the women had foetal cells in all of these tissues. The researchers knew that the cells were from the foetus, and not from the mother, because the cells contained a Y chromosome (found only in males) and the women had all been carrying sons! In some cases, foetal cells may stay in a woman's body for years or even a lifetime (4). 

The studies suggested that there is a potential for both positive and negative consequences of microchimerism in the brain  for a number of different diseases that affect the brain, including degenerative diseases and cancer. 

Chimerism might cause problems in forensic studies where the criminals are nailed using DNA analyses. It could also lead to confusion around a victim's identity.

Previous work on microchimerism suggested foetal cells might protect against breast cancer and aid tissue repair in the mothers, but also could boost the risk of colon cancer and help incite autoimmune diseases, in which a person's body is mistakenly attacked by its own immune system.

But the research results are not very clear at this stage and further investigations are needed to come to a conclusion in this regard .

Can a person who does not exist have children? 

Yes! I t is possible!

Chimerism: A man who never existed had a child (6,7)

Clearly, you should be thinking: “How can someone who never exist have a child?”

Well, here is the real story…

The couple decided that he’ll take a 23andMe test, and the results shocked them even more.

The father was actually the uncle.

This couldn’t make sense, though, since the child was made through Vitro fertilization, and only the father was giving the sperm sample.

What the father learned from this changed his entire perspective on who he was as a person.

The father was a chimera who absorbed his fraternal twin, who also happened to be a male.

Inside, the father’s sperm was 90% himself and 10% his twin brother.

His son only inherited the absorbed brother’s sperm, though.

From this, a man who was never born managed to have a child of his own.

Citations:

1. G.W. Bird et al., “Further observations on the Birmingham chimaera,” J Med Genet, 13:70-71, 1976.

2. W.M. Watkins et al., “A human dispermic chimaera first suspected from analyses of the blood group gene-specified glycosyltransferases,” J Immunogenet, 8:113-28, 1981.

3. http://www.nature.com/bmt/journal/v34/n1/full/1704525a.html

4. http://www.livescience.com/23490-fetal-dna-mom-brain.html

5. https://www.thesun.co.uk/news/10515134/man-dna-changed-bone-marrow-...

6. Human Chimera: How a Man's Unborn Twin Fathered His Child | Time

 7.  Human-Nonhuman Chimeras: Do We Really Want to Go There? | The ...

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