MedTerms Medical Dictionary

Y chromosome: The sex chromosome found together with an X chromosome in most normal males. Once thought to be a genetic wasteland, the Y now is known to contain at least 20 genes, some of them unique to the Y including the male-determining gene and male fitness genes that are active only in the testis and are thought responsible for the formation of sperm. Other genes on the Y have counterparts on the X chromosome, are active in many body tissues and play crucial "housekeeping" roles with the cell. A number of specific genes have been Y-linked including:

• ASMTY (which stands for acetylserotonin methyltransferase),
• TSPY (testis-specific protein),
• IL3RAY (interleukin-3 receptor),
• SRY (sex-determining region),
• TDF (testis determining factor),
• ZFY (zinc finger protein), PRKY (protein kinase, Y-linked),
• AMGL (amelogenin),
• CSF2RY (granulocyte-macrophage colony-stimulating factor receptor, alpha subunit on the Y chromosome),
• ANT3Y (adenine nucleotide translocator-3 on the Y),
• AZF2 (azoospermia factor 2),
• BPY2 (basic protein on the Y chromosome),
• AZF1 (azoospermia factor 1),
• DAZ (deleted in azoospermia),
• RBM1 (RNA binding motif protein, Y chromosome, family 1, member A1),
• RBM2 (RNA binding motif protein 2) and
• UTY (ubiquitously transcribed TPR gene on Y chromosome).

The Y is a useful chromosome for tracking men because it is transmitted unchanged from father to son. The Y escapes the intergenerational shuffle (recombination) that affects genes on the X chromosome and the remainder of the genome. All men have essentially the same Y chromosome. It is thought that in our small ancestral population some men had no children or only daughters, so that some Y chromosomes disappeared until only one was left. This ubiquitous Y has the same DNA in every man on earth except for the mutation that crops up every millenium and is then inherited by all males descended from that man.

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