Many mothers I know, no matter how old their kids are, tell me they feel their children continue to be part of them long after birth. Despite decades having passed since the umbilical cords were cut, the ties connecting mothers to their kids can feel strong and eternal.
It appears that a strange genetic truth backs up those instincts. Mothers might think continually of their children, but recent genetic studies show mothers also physically retain bits of their kids in their bodies and their brains.
During pregnancy, the placenta interfaces between mother and fetus. This organ consists of cells from both mother and child, and permits the mother to supply the developing fetus with oxygen, hormones and nutrients.
It also provides an avenue for the fetus to expel its own carbon dioxide and waste through the mother’s body.
Entire cells cross the placenta in both directions throughout a pregnancy.
Now, multiple research studies show that a child’s genetic material can reside within the mother for decades after the child is born. The cells, with their unique genetic coding, may collect in the mother’s skin, liver, spleen, kidneys, heart, muscles, thyroid and lungs.
Research published last year indicates it even infiltrates the mother’s brain.
All this came to light when genetic scans of women revealed — against all expectation and common sense — DNA that could come only from men.
All women carry two X chromosomes in their genetic-makeup bags. Guys distinguish themselves by packing just one X chromosome, as well as one Y chromosome.
From that single, teeny, male-only Y chromosome spring beards, hairy chests, rampant teenage testosterone, a childhood predilection for fart humour that can endure for decades, smelly locker rooms and all the other trademarks of guyhood that we’ve come to know and love.
The Y chromosome demonstrates how even the smallest things can have huge effects.
Women’s DNA has no Y chromosome. Scientists had no reason to expect to find male DNA lurking inside female mice or humans or any other mammal.
But, to paraphrase Sesame Street’s 1970 kiddie classic, some of the DNA found in women was not like the others. Some of the DNA didn’t belong.
That genetic material bore the signature of the Y chromosome.
The scientists fingered the obvious culprits — the women’s sons. They determined that cells from son-fetuses cross the placenta to take up residence in mothers’ bodies. The genetic scans were picking up the male-only DNA within those cells.
They identified other sources, too. These include blood and organs donated by men.
The cells in those tissues would mix with the new hosts’ cells.
The scientists zeroed in on male DNA. However, that doesn’t mean female DNA stays barefoot and pregnant at home. It is very likely as adventurous as male DNA. The thing is, X-chromosome material from daughters or other women is much harder than Y-chromosome material to pick out from genetic material that is normally found — and expected to be found — in both women and men. After all, both guys and gals carry X chromosomes.
Nonetheless, the cellular soup thickens.
Some women found to harbour male DNA were neither mothers nor blood- or organ-transplant recipients. Researchers concluded that the male DNA inside these women originally belonged to their older brothers. The cells that male fetuses donate to their mothers might later end up being incorporated into the bodies of younger sisters and brothers.
By extension, cell-swapping across the placenta would also have occurred when Mom was in the womb. This means children could carry the cells of their mother’s older brothers and sisters, as well as those of their own older siblings.
Suddenly, all this sharing of cells makes the concept of family divide and multiply like a fertilized egg.
As the youngest child of a mother who was a youngest child, I feel compelled to paraphrase Sister Sledge’s 1979 rhythm-and-blues classic. We are family. I got all my sisters (and brothers, and my mother and her brothers and sisters) in me.
Happy Mother’s (and whoever else’s cells she carries) Day.