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Chromosomal sex determination

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    A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. Occasionally, there are hermaphrodites in place of one or both sexes. There are also some species that are only one sex due to parthenogenesis , the act of a female reproducing without fertilization. In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. The sexual differentiation is generally triggered by a main gene a "sex locus" , with a multitude of other genes following in a domino effect.
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    The Sex Chromosomes and Sex Determination

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    “I’m XY and I Know It”: Sex Determination Systems - Science in the News

    NCBI Bookshelf. Primary sex determination is the determination of the gonads. In mammals, primary sex determination is strictly chromosomal and is not usually influenced by the environment. In most cases, the female is XX and the male is XY. Every individual must have at least one X chromosome. Since the female is XX, each of her eggs has a single X chromosome. The male, being XY, can generate two types of sperm: half bear the X chromosome, half the Y.
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    Sex-determination system

    This page has been archived and is no longer updated. Whether an animal will become a male, a female, or a hermaphrodite is determined very early in development. Scientists have worked for hundreds of years to understand the sex-determination system.
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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. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell.
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