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).
If I'm not mistaken..
The SRY gene is the only gene that cause variance in sex determination. Of course, many genes are then involved in sex determination cascade but none these genes have variance in humans 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.
Purely theoretically speaking, in all species, the sex is determined by both the environment and 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.
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.
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.