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Medical Definition of Y map
1. The array of genes on the y chromosome. 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. (12 Dec 1998)