ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
X chromosome. Computer artwork of a human X chromosome (blue/purple, centre). Other chromosomes are seen at top right and lower left. The X chromosome is one of two sex chromosomes. It is seen here as a pair of identical chromosome copies, called chromatids. These run parallel to each other, and are joined at an area called a centromere. A chromosome is partly made up of the genetic material DNA (deoxyribonucleic acid), and so carries the inherited characteristics of a human. Most human cells contain 46 chromosomes as 23 pairs, of which one pair are the sex chromosomes. A female has two X chromosomes and a male has one X and one Y chromosome.
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