BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY BIOPHOTO ASSOCIATES / SCIENCE PHOTO LIBRARY
Human X and Y chromosomes, coloured scanning electron micrograph (SEM). Each chromosome has replicated to form an identical copy, or chromatid, to which it is joined. The combination of sex chromosomes inherited during fertilization determines a person's sex. Males inherit an X and a Y chromosome (as seen here), whilst females inherit two copies of the X chromosome. The Y chromosome carries instructions for the development of male characteristics. The sex chromosomes are one pair of 23 present in most cells of the body. Chromosomes contain the genetic material DNA (deoxyribonucleic acid).
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