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Nondisjunction of Chromsomes

Nondisjunction of Chromsomes. Mistakes made during meiosis can lead to abnormal numbers of chromosomes. This occurs when a homologous pair of chromosomes fail to separate. These mistakes can occur in either meiosis I or II. Trisomy 21.

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Nondisjunction of Chromsomes

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  1. Nondisjunction of Chromsomes

  2. Mistakes made during meiosis can lead to abnormal numbers of chromosomes. • This occurs when a homologous pair of chromosomes fail to separate. • These mistakes can occur in either meiosis I or II.

  3. Trisomy 21 • Occurs when there is nondisjunction during meiosis I. Half the gametes will carry an extra chromosome 21. • A person with an extra chromosome 21 is said to have down syndrome.

  4. Trisomy 21 affects about 1/700 children in the USA. • People with down syndrome generally have a shorter lifespan, and will exhibit varying degrees of developmental delays.

  5. Other physical characteristics include a round face, flattened nose bridge, small teeth, short stature, heart defects, and susceptibility to respiratory infections. • Most people with down syndrome are also sterile, and therefore unable to have children.

  6. The occurrence of trisomy 21 increases with the age of the mother. • Women who are over 30 have a 1% chance of having a child with down syndrome. This risk increases with older mothers. • Women over 35 can have genetic testing done to find out if their fetus has trisomy 21.

  7. Klinefelter Syndrome • Occurs when there is nondisjunction in the sex cells. • Klinefelter’s occurs in males who have an extra X chromosome.

  8. Males with klinefelter’s will have smaller testes, some breast development, lanky, and poor facial hair. • These males are also sterile. Therefore many men do not realize that they have an extra X chromosome until they wish to start a family of their own.

  9. Turner Syndrome • Occurs in females because of the nondisjunction of sex cells resulting in females with only one X chromosome. • Women with turner syndrome have a webbed neck, poor development ovaries (sterile), short stature, broad chest, heart defects, and increased weight.

  10. XYY Males • Males with XYY generally have regular fertility and regular physical characteristics.

  11. XXX Females • Women who have three X chromosomes usually do not experience any physical or mental characteristics due to the disorder. • In females only 1 X chromosome will be active in each cell.

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