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22. Variation And Genetics eLearn.Punjab

Humans have 46 chromosomes in the form of 23 pairs. 22 pairs are of autosomes
and one pair is of sex-chromosomes. Autosome pairs are common in both the sexes
but the 23 rd sex chromosome, pair is very different in males and females (Fig. 22-
19). A woman has two similar X chromosomes in her 23rd pair but a man has an X
chromosome along with a much shorter Y chromosome in his 23rd pair. The 23rd pair
in man is heteromorphic. She is XX but he is XY.

SRY is the male determining gene. It is located at the tip of short arm of Y-chromosome.
Its name SRY stands for “Sex determining regions of Y.”

Fig 22.19 Sex Chromosomes of a man

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