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It's very well known that the Y chromosome is what determines maleness, but more specifically this seems to happen thanks to the SRY gene located on it. Some individuals have an XX karyotype, but because of unequal crossing-over between X and Y chromosomes during meiosis in the father, one of the X chromosomes ends up containing the SRY gene, and the individual develops into a male (De La Chapelle Syndrome). So I was wondering, is the SRY gene all that's really needed for an individual to be, unquestionably, a male? It's kinda odd how XX males have male genitalia but are classified as intersex solely because their karyotype is a typical feminine one (which should be irrelevant given how they also possess the SRY gene).

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No. The SRY gene is an RNA inhibitor gene. If its target is altered to not match, you get an XY female. – Joshua Oct 5 '15 at 22:58

To my knowledge, the SRY gene is the only gene that cause variance in sex determination in humans. Of course, many genes are then involved in sex determination cascade but none these genes have variance in humans. Because environmental variance has no impact on gene determination in humans (to my knowledge and despite a few highly criticized articles) and therefore, nothing else than the SRY gene explains the sex determination.

The genes that are involved in the cascade of sex determination are not necessarily on the sexual chromosomes. On the Y chromosome, there are some genes that are male beneficial (beneficial for the male function) but these genes are not involved in the sex determining system.

In all species, the sex is determined by the environment and/or the genes. The best way to look at it is by reaction norms. On the below picture, think of the x-axis as being the temperature. Then, if you ask the question "Does the temperature influence the probability to develop into one sex or another?" One should answer. "It depends on the range of temperature you're looking at!" If you look at only very high temperature (far right) or very low temperature (far left), only the genotype explains the sex determination. If you look at mid-range of temperature, then both the genotype and the environment determines the sex.

enter image description here

N. Perrin and L. Beukeboom are writing what is probably going to be a very good book that will obviously interest you. I think the book is going to be publish in 2014 only. Here is the amazon link to pre-command it.

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Check out this recent article in Science (AOP).

They say that two genes- Sry and Eif2s3y are sufficient to provide the entire functionality of the Y chromosome. Alhough, there is reduced number of spermatids in these mice (Genotype :XO-Sry-Eif2s3y), the viable ones are able to give rise to healthy offsprings.

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The question did not have to do with male functionalities but with sex determination system. What matters for this question are the loci which variance bring some variance in sex determination. – Remi.b Nov 29 '13 at 21:23
read the article.. it is quite interesting.. what it says is that two genes can suffice for the entire Y chromosome (in the process of sex determination and also to retain the ability to reproduce). – WYSIWYG Nov 30 '13 at 9:39
From what I read of the abstract, it doesn't seem that the gene Eif2s3y has some polymorphism in nature. Therefore, this gene does not influence the variance in sex determination. But when I read the OP's question again, I realize that I might have misunderstood his point. This article seem very interesting indeed and might answer to OP's question. – Remi.b Nov 30 '13 at 9:50

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