BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Female chromosomes. Coloured light micrograph of 46 chromosomes from a normal human female. This constitutes the full karyotype, that is the total number of chromosomes found in each cell of the female human body. Each cell contains 22 matched pairs of chromosomes, and one sex-determining pair. Female and male sets of chromosomes differ only in the pair of sex chromosomes (at bottom right). A female is labelled XX, and a male XY. A normal female karyotype is written: 46,XX. The chromosomes are made up mainly of DNA, some proteins (principally histones), and small amounts of RNA. Chromosomes carry genes that determine the characteristics of an individual.
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