Non-disjunction and the karyotypes it makes.

Meiosis with a chosen non-disjunction (MI or MII, mother or father) and the karyotypes it gives: 47,XXY, 45,X0, trisomy 21.

Produce a Klinefelter (47,XXY) zygote and then a Turner (45,X0) zygote.

Swapping the karyotypes of Klinefelter's and Turner's syndromes.

• Chromosomal disorders result when one or more chromosomes are absent, in excess, or abnormally arranged.
• Aneuploidy is a gain or loss of chromosomes caused by failure of chromatid segregation during cell division. Polyploidy is an increase in whole chromosome sets caused by failure of cytokinesis after telophase, and is often seen in plants.
• Trisomy means an extra copy of one chromosome; monosomy means one chromosome is missing.
• Down's syndrome is trisomy of chromosome 21, first described by Langdon Down in 1866. Affected people are short with a small round head, furrowed tongue and partly open mouth, have a broad palm with a characteristic crease, and show delayed physical, psychomotor and mental development.
• Klinefelter's syndrome has an extra X in a male, giving 47, XXY. The person has an overall masculine build but also some feminine features such as breast development (gynaecomastia), and is sterile.
• Turner's syndrome is the absence of one X in a female, giving 45, X0. These females are sterile, with rudimentary ovaries and a lack of other secondary sexual characters.

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