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Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness: one X chromosome gives putative maleness, but the presence of Y chromosome genes is required for normal male development. In the fruit fly individuals with XY are male and individuals with XX are female; however, individuals with XXY ...
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
•List of human protein-coding genes page 4 covers genes SLC17A8–ZZZ3 NB: Each list page contains 5000 human protein-coding genes, sorted alphanumerically by the HGNC-approved gene symbol. Follow the Python code link for information about updates to the list of genes on these pages.
Females therefore have 23 homologous chromosome pairs, while males have 22. The X and Y chromosomes have small regions of homology called pseudoautosomal regions. An X chromosome is always present as the 23rd chromosome in the ovum, while either an X or Y chromosome may be present in an individual sperm. [4]
N-Acetylserotonin O-methyltransferase is an enzyme that is coded for by genes located on the pseudoautosomal region of the X and Y chromosome, and is most abundantly found in the pineal gland and retina of humans. [8] The structure of N- Acetylserotonin O-methyltransferase has been determined by X-ray diffraction. [9]
The SHOX gene in the PAR1 region is the gene most commonly associated with and well understood with regards to disorders in humans, [17] but all pseudoautosomal genes escape X-inactivation and are therefore candidates for having gene dosage effects in sex chromosome aneuploidy conditions (45,X, 47,XXX, 47,XXY, 47,XYY, etc.).
The chromosome is ~193 megabases in length. In a 2012 paper, 775 protein-encoding genes were identified on this chromosome. [4] 211 (27.9%) of these coding sequences did not have any experimental evidence at the protein level, in 2012. 271 appear to be membrane proteins. 54 have been classified as cancer-associated proteins.
The amelogenin gene has been most widely studied in humans, where it is a single copy gene, located on the X and Y chromosomes at Xp22.1–Xp22.3 and Yp 11.2 [5]. [3] The amelogenin gene's location on sex chromosomes has implications for variability both between the X chromosome form and the Y chromosome form (), and between alleles of AMELY among different populations.