User:Mehnazt/sandbox

Main article draft 3 (please peer review this draft):

On a deeper level, however, sex determination goes beyond the acquirement of XX or XY sex-chromosome pairs. There are questions about how, on a molecular level, allosomes influence the creation of “femaleness” or “maleness.”

Previous theories on Sex Determination

Ever since the discovery of X-inactivation through research into Calico cats, it has been postulated that X-inactivation plays a role in genetic sex determination in humans. Initially, there were many theories as to how exactly X-inactivation influences sex. To understand one such theory, you can take the following scenario into consideration: a DNA sequence that is concerned with the creation of a male-trait is regulated by a regulatory DNA sequence. If the regulatory DNA sequence allows the main sequence to be expressed, the male-trait will appear in the phenotype, otherwise not. An explanation for this theory is that the X-chromosome simply inactivates in the presence of another X-chromosome; this causes XX-chromosome humans to have a lower frequency of the regulatory gene (given that both X and Y chromosomes have an equal frequency of the regulator) and so the expression of the male trait is prevented from appearing in the phenotype.

Sex Determination as understood today

Theories like the one above have become redundant now, however. In the past, there wasn’t much evidence supporting the idea that X-chromosome inactivation occurred due to dosage compensation. At present, it is believed that one X-chromosome in female humans is inactivated (twisted in a Barr body so that its DNA sequences can’t be accessed). This leaves only one functioning X-chromosome in both male and female humans, thereby equalizing “dosage.”

But dosage regulation isn’t all there is to genetic sex determination. There is a gene in the Y-chromosome that has regulatory sequences that control genes that code for maleness. This gene is called the SRY gene. The SRY sequence’s prominence in sex determination was discovered when the genetics of sex-reversed XX men (i.e. humans who possessed biological male-traits but actually had XX allosomes) were studied. After examination, it was discovered that the difference between a typical XX individual (traditional female) and a sex-reversed XX man was that the typical individuals lacked the SRY gene. It is theorized that in sex-reversed XX men, the SRY mistakenly gets translocated to an X-chromosome in the XX pair during meiosis. Any how, this experimentation had proved the SRY gene’s role in genetic sex determination.

Other vertebrates and plants

It is argued that humans have developed a complex system of genetic sex determination due to their status as highly complex chordates. Lower chordates, such as fish, amphibians and reptiles, have systems that are influenced by the environment. Fish and amphibians, for example, have genetic sex determination but their sex can also be influenced by externally available steroids and incubation temperature of eggs. In reptiles, only incubation temperature determines sex.

Many scientists argue that Sex Determination in flowering plants is more complex than that in humans. This is because even the flowering plant subset has a variety of mating systems. Their Sex Determination is primarily regulated by MADS-box genes. These genes code for proteins that form the sex organs in flowers.

Understanding Sex Determination in other taxonomic groups allows us to understand human Sex Determination better, as well as place humans in the phylogenetic tree more accurately.

Feedback response:

I really appreciated the feedback from my reviewers. I added sub-headings, more links (to complex ideas) and examples. I also searched the article for colloquialisms and other language issues and tried to remove them.

I have to address some advice that I either could not or should not take into consideration. Firstly, I don't think I can add examples from fauna taxonomic groups; they wouldn't be appropriate for the Wikipedia article as a whole. But I have included and compared examples of vertebrates that I think are relevant. Secondly, I cannot find a free-to-use image, even though I really want to add an image. Images that are free by Wikipedia standards are hard to come by and I'm still looking for one. Lastly, I'm on the fence about the language of the article; one reviewer said it needed improvements but another said it was good. I think the language is good for the most part but it may need some fixing before finalization.

A note: I had added links to other articles last week but both reviewers did not see them. At least one of them should have been able to see the links. This may be some sort of glitch(?) I don’t know.