The Genetic Origin of Sex: the X and Y Sex Chromosomes

Sex hormones are responsible for giving a person the physical characteristics of their genetic sex. Naturally, the way they work differs depending on each person’s sex chromosomes.
In light of the above, men and women have a different number and type of sex chromosomes.
Males have XY and females have XX. These chromosomes contain the keys that trigger the regulation of sex hormones in men and women, which their sexual characteristics will depend on.
In organisms that have a different number number of sex chromosomes for men and women, a process has been developed that eliminates the difference in the number of gene doses linked to the X chromosome. This means that because females have two copies of the X chromosome, the genes bound to it will be duplicated. That is, this happens unless one of them is inactivated.
Gene dosage compensation

How does the X chromosome inactivation process happen?

- First, either the selection of the X chromosome that will remain active,
- or the selection of the X chromosome that will remain inactive.
Scientists discovered this after studying triple X syndrome. This is a genetic disease characterized by the presence of an extra X chromosome (XXX).
In people who suffer from this syndrome, two of their X chromosomes randomly inactivate. This supports the theory that the mechanism which governs the chromosomal inactivation process is the selection of the X chromosome that will remain active.
Overall, the silencing of the X chromosome is an epigenetic phenomenon that has intrigued scientists for decades.
In general, the vast majority of genes express themselves in two chromosomal copies (remember that the human being has 22 pairs of autosomes). However, this is not possible in sex chromosomes. This is because the number of X and Y chromosomes differs between the two sexes.
Visible consequences of chromosomal inactivation

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.
- Crawford D, Dearmun A. Klinefelter syndrome. Nurs Child Young People 2017; 29: 19.
- Otter M, Schrander-Stumpel CT, Curfs LM. Triple X syndrome: a review of the literature. Eur J Hum Genet 2010; 18: 265-71.
- Priyadharscini RA, Sabarinath TR. Barr bodies in sex determination. J Forensic Dent Sci 2013; 5: 64-7.
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