XX and XY do not determine sex; polygenic expression does that instead. XX does not always and inevitably equal only female, and XY does not always and inevitably equal only male:
In mammals, the transcription factor SRY, encoded by the Y chromosome, is normally responsible for triggering the indifferent gonads to develop as testes rather than ovaries. However, testis differentiation can occur in its absence. Here we demonstrate in the mouse that a single factor, the forkhead transcriptional regulator FOXL2, is required to prevent transdifferentiation of an adult ovary to a testis. Inducible deletion of Foxl2 in adult ovarian follicles leads to immediate upregulation of testis-specific genes including the critical SRY target gene Sox9. Concordantly, reprogramming of granulosa and theca cell lineages into Sertoli-like and Leydig-like cell lineages occurs with testosterone levels comparable to those of normal XY male littermates.
Our results show that maintenance of the ovarian phenotype is an active process throughout life. They might also have important medical implications for the understanding and treatment of some disorders of sexual development in children and premature menopause in women…
Geneticist Sophia Siedlberg has been telling us this for ages, based on computer modeling. It is good that the facts she has been pointing out for so long are now being vindicated in. In her commentary about this research at Intersex News – see the link below – Sophia writes:
… But the one thing I will benefit from is knowing that because of this latest discovery by Dr. Robin Lovell-Badge’s team I will be regarded as a human being instead of a monster, not because I was aware of the possibility that such research would incidentally prove me correct. I can call myself “genetically me”….
…finally there is a degree of understanding that people who do not fit the classical biological definitions of what is male or female are not “dangerous” or “evil” or a “threat to society” – they are just natural variations of the human genome. Genetically we are us….
- Cell – Females Battle to Suppress Their Inner Male
- Cell – Somatic Sex Reprogramming of Adult Ovaries to Testes by FOXL2 Ablation
- Intersex News – Vindicated! by Sophia Siedlberg
- PopSci.com.au – Switching a Gene in Adult Mice Easily Transforms Females Into Males
- The Independent – From Minnie to Mickey (and all they did was turn off a gene)
- Times Online – Caster Semenya and the middle sex – this article quotes Sophia.
- Times Online – Scientists find single ‘on-off’ gene that can change gender traits
- Trends in Genetics – Sex determination and SRY: down to a wink and a nudge?