Definition of X (in genetics)

X (in genetics): Although the letter X can be used as a symbol in various ways (such as with X-rays, the X-axis of a graph, etc.), "the X " in genetics and medicine today usually refers to the X chromosome.

The X is the sex chromosome that is found twice in chromosomally normal females and singly along with a Y chromosome in chromosomally normal males. The complete chromosome complement consisting of 46 chromosomes including the two sex chromosomes is thus conventionally written as 46,XX for chromosomally normal females and 46,XY for chromosomally normal males.


Last Editorial Review: 6/14/2012

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