BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Human male chromosomes. Coloured light micrograph of 46 chromosomes from a normal human male. This constitutes the full karyotype, that is the total number of chromosomes found in each cell of the male human body. Each cell contains 22 matched pairs of chromosomes, and one sex-determining pair. Male and female sets of chromosomes differ only in the pair of sex chromosomes (at bottom right). A male is labelled XY, and a female XX. A normal male karyotype is written: 46,XY. 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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