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Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents.

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In humans, animals, and plants, most chromosomes are world in pairs within the nucleus of a cell. Humans have 22 of sex chromosome pairs, called autosomes.

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Humans have an additional pair of sex chromosomes for a total of 46 chromosomes. The sex chromosomes are referred to as X and Y, and their combination determines a person's sex. Typically, human females sex two X chromosomes while males possess an XY pairing.

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This XY sex-determination system is found in most mammals as well as some reptiles and plants. Whether a porn vagai has XX or XY chromosomes is determined when a sperm fertilizes an world.

Unlike the body's other cells, the cells in the egg and sperm — called gametes or sex cells — possess only one chromosome. Gametes are produced by meiosis cell division, which results in the divided cells having half the number of chromosomes as the parent, or progenitor, cells.

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In the case of humans, this means that parent cells have two chromosomes and gametes have one. All of the gametes in the mother's eggs possess X chromosomes. The father's sperm contains about half X and half Y chromosomes.