I hope this isn’t as vague as I think it’s going to be. For some reason, this has been bugging me…I can’t think of the name of a condition or conditions that I read about awhile back.
I remember reading a Wiki article about humans who had two types of DNA in their bodies. I believe this was cause by some anomaly in utero. It was either a parasitic or absorbed fraternal twin situation or something caused by absorbing part of the mother’s biological material prior to birth. If I remember correctly, the condition wasn’t life-threatening or otherwise detrimental but it seems that there was some sort of skin/pigmentation “strangeness” that resulted.
Does this ring a bell for anyone? It’s merely something I’m curious about and I’ve been unable to come up with the appropriate key words in order to find anything related.
I remember it coming up in an episode of CSI a few years back. Apparently there are different types, and it’s very rare in humans.
ETA: Dammit, too slow!
Strictly speaking, all humans have two types of DNA in their bodies: nuclear and mitochondrial. Nuclear DNA resides in the cell nucleus and each parent contributes one half of its makeup; what is termed the genome. Mitochondrial DNA resides in the mitochondria and is passed along from mother to offspring.
Chimerism is more accurately described as one person with two distinct genomes. All the mitochondrial DNA in a chimera is the same.
Strictly speaking all women (all with a normal DNA complement) are chimeric to a mild degree. Here is how that comes about. Men have one X and one Y chromosome (normally, I will stop saying that). There are only a handful of genes on the Y and most are involved in sexual characteristics. Women have two X chromosomes and if they are both active, this would produce too many of whatever proteins are coded by the genes on the X. So somewhere along the evolutionary path, a mechanism was developed whereby in each cell, one of the two X chromosomes is deactivated and reduced to a shriveled particle in each cell. But the cells do this at random and so 50% of the cells will have one of the two X chromosomes and 50% will have the other. So women’s cells are not uniform the way men’s are.
As I write this I wonder if some sex-linked recessives appear partially in women. For example, color blindness, at least red/green, is a sex-linked recessive. Would a woman one of whose X chromosomes has the defective gene have poor color discrimination because half the cones are defective? Or could a carrier of a baldness gene have thinning hair as she ages? I am sure these questions have been asked before–and doubtless answered.
There is also some non-nuclear genomic material floating around that is not in mitochondria. Most of it appears to be non-functional, possibly a legacy of other synergestic partnerships like that which formed mitochondria albeit without apparent use at this point.
It is also possible to have more than one “type” of mitochondria, and I’ve read some speculation that paternal mitochondria can sometimes invade the embryo if not fully destroyed during embryogenesis. This can lead to a number of different chronic disorders or hybridization of mitochondria.
What the o.p. is referring to, as already noted, is chimerism. Their is also mosaicism, in which a body contains colonies of genetically distinct organisms. This often occurs in trisomic disorders like Klinefelter’s syndrome or XYY syndrome.
Strictly strictly strictly strictly speaking, all humans have hundreds or thousands of different DNA sequences in their cells, as cells pick up random mutations throughout life. They’re not significant differences, though.
I had no idea. I was always under the impression that gene expression in the XX pair was just like in the other chromosomes – the whole dominant, recessive, co-dominant, etc., bit.
Actually, if she has an even mix of the normal and certain types of atypical cones due to such a mechanism she could have better color vision than the norm, as she will be able to perceive more distinctions that a person with normal cones. And such women, although rare, have been documented.
Women can also be colorblind if the majority of their retina cells opt for the atypical gene rather than the normal one, in which case she’s a carrier with symptoms. Such a woman may be detectably colorblind, but not as impaired in color perception as men with the same atypical gene or other women with the same genes. Indeed, I may be such a woman, as the Ishihara color test does show me a colorblind but several other color vision tests do not. In other words, I clearly have the atypical gene, but with rare exception (like testing looking for the trait) it never seems to be an issue.
Certainly, other X-linked recessive traits could have similar manifestations.
There was an article in a recent issue of either SciAm or Discover discussing that it is often possible to find DNA from one’s mother in one’s own tissues - regardless of whether the person is male or female.
The article also said that women who have borne children - or at least been pregnant for some appreciable period - may carry cells from those progeny for the rest of their lives. So it is possible for a woman who has reproduced to have DNA belonging to her own mother, and also of each and every child she has carried.
The article did not go into detail as to the underlying research what organs, or mention which site(s) are most likely to contain such cells, nor did it say what the frequency of those cells would be. So chimeras - and those who would have been twins, had their fellow uterine tenant survived - aren’t the only ones who carry human cells not their own.
If someone gets a bone marrow transplant, wouldn’t they also have two types of DNA - presumably their own, and then that of the donor from the red blood cells made by the marrow? or is my understanding of biology screwed up after all these years?
Perhaps you misunderstood what I said. Recent reports have indicated that they have recovered mothers’ cells from their children, and vice versa. I was not referring to the 50% of each parent’s DNA that each individual from a species that reproduces sexually receives.
Not only that, but you can track how well a bone marrow transplant is progressing by doing a chimerism test - you sequence the bone marrow DNA and see how much of it is from the donor and how much is from the recipient. That way you can track it through time and see if the transplanted material is growing well.
