I found this fascinating study that suggests chimerism is much more prevelent

than we thought and also can explain why some people are homosexual or transgendered.

First I do not know how well this is accepted; if it even accepted and it is from about 10 years ago. But I have read about people who have two different genomes in their bodies and we really have no idea how many people that happens to. There was one story of a woman whose children came out with different DNA than they "should have" as her children.

And please, this is just information. I am not trying to be insulting to anyone and I sincerely hope this information is not insulting. I identify as a bisexual woman and I have no idea how I came to be bisexual. It would be interesting to find out though.

Here is a definition of microchimerism - "Microchimerism is defined as the presence of two genetically distinct cell populations in the same individual. It can arise from several causes including the bidirectional transfer of cells between mother and fetus during pregnancy, twin-to-twin transfer in utero, from organ transplantation, and blood transfusion."

Chimera - "A genetic chimerism or chimera (/kaɪˈmɪərə/ ky-MEER-ə or /kɪˈmɪərə/ kə-MEER-ə, also spelled chimaera or chimæra) is a single organism composed of cells with more than one distinct genotype. In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, subtle variations in form (phenotype) and, if the zygotes were of differing sexes, then even the possession of both female and male sex organs[1] (this is just one of many different phenomena that may result in intersexuality). Animal chimeras are produced by the merger of multiple fertilized eggs."

DUAL-GENDER MACRO-CHIMERIC TISSUE DISCORDANCE IS PREDICTED TO BE A SIGNIFICANT CAUSE OF HUMAN HOMOSEXUALITY AND TRANSGENDERISM
Brian P Hanley

ABSTRACT

I present literature evidence that suggests that human chimerism may be quite common, occurring in between 5% and 15% of people. Chimerism has been believed to be rare because it usually presents without visible phenotype. In addition to the documented occurrence of dual gender macrochimeras with true hermaphrodite phenotype, there are reports of the occurrence of other natural human macrochimeras. The literature reviewed in this paper suggests that such macrochimerism is much more common than usually appreciated. Chimerism occurs in a patchy manner, with male cells outgrowing female in macrochimerism causing the majority to be phenotypically male. The literature also suggests that the sex of nervous system tissue is the primary determinant in higher animals of sexual attraction. From this, the existence of human macrochimeras in which large proportions of cells are male and female is predicted to have a correlation with homosexuality and transgender self-identification because in many such cases, the central nervous system, or crucial parts of it, will be of one sex and the gonads and body form will be of the opposite sex. I describe experiments to further clarify this hypothesis, which can also have potential benefit beyond this specific question.

http://www.hy-ls.org/index.php/hyls/article/view/57/0