Chromosomes are made of a tightly coiled strand of DNA around proteins (called histones). However, they are
not visible until prophase of cell division when they assume this condensed form. Chromosomes contain genes that carry
'instructions' for hereditary information, which are passed from parent cells to daughter cells during cellular division,
and from parent to child during fertilization. Humans normally have 23 pairs of chromosomes.
What is unique about Chromosome X?
Not only does chromosome X have a cooler name than any other chromosome, but it is one of two sex chromosomes.
Females normally have two X chromosomes, whereas males have an X and a Y chromosome (the other sex chromosome). Because
females have two X chromosomes and the information from only one is needed, one of the chromosomes is permanently inactivated
within all somatic cells during early embrionic development.
The X chromosome contains between 900 and 1,400 genes.
