Within their coiled strands, chromosomes hide a world of information about how a person should look, how tall he should be, what should be his skin color and also the diseases that he may be prone to (which are referred to as genetic disorders in human). They have this information coded in the form of nucleotide sequences that form DNA (dioxyribonucleic acid) molecules. A single molecule of DNA is coiled to form a single chromosome. These chromosomes are present in pairs. Human beings have 23 pairs of chromosomes or 46 chromosomes in all. Of them, 1 pair forms the sex chromosomes. The rest 22 pairs are the autosomes. Sex chromosomes are of two types - X and Y. A man has one X and one Y chromosome (XY) while a woman has two X chromosomes (XX). It is just the difference of one sex chromosome that decides an individual's gender.

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