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Atypical Meiosis

Atypical Meiosis. Abnormal Cell Division. Nondisjunction – Failure of chromosomes to separate during cell division One daughter cell will have too many chromosomes and the other will have too few May occur during mitosis or meiosis Mitosis – cell usually dies, no impact on organism

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Atypical Meiosis

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  1. Atypical Meiosis

  2. Abnormal Cell Division • Nondisjunction – Failure of chromosomes to separate during cell division • One daughter cell will have too many chromosomes and the other will have too few • May occur during mitosis or meiosis • Mitosis – cell usually dies, no impact on organism • Meiosis – If a sex cell with an abnormal number of chromosomes is fertilized, every cell of the resulting embryo will be abnormal. (May occur in meiosis I or meiosis II)

  3. Normal meiosis MEIOSIS I Replicate DNA Results of crossing-over not shown MEIOSIS II Normal monosomic gametes

  4. Nondisjunction during meiosis I MEIOSIS I Replicate DNA Non-disjunction MEIOSIS II Disomic gametes Nullisomic gametes

  5. Nondisjunction during meiosis II MEIOSIS I Replicate DNA MEIOSIS II Non-disjunction Disomic Nullisomic Monosomic Monosomic gametes

  6. Parent 1 Parent 2

  7. Too much or too little DNA • A change in the amount of genetic information (especially a whole chromosome) is not well tolerated; the resulting embryo usually dies. • Changes may occur with autosomes or sex chromosomes • Changes are better tolerated with sex chromosomes

  8. Monosomy – only 1 copy of a chromosome is present instead of 2 • Trisomy – 3 copies of a chromosome are present instead of 2 • Most nondisjunction events are fatal; pregnancy usually results in a miscarriage. • Problems resulting from nondisjunction provide clues about what information is on each chromosome

  9. Examples of (survivable) nondisjunction

  10. Madison…

  11. A karyotype is often used to diagnose nondisjunction disorders Karyotype of human (female)

  12. What is the gender of this person? How can you tell? What do you notice in this chart that may indicate that an error has occurred? What condition would this person have?

  13. AN EXTRA COPY OF CHROMOSOME 21 CAUSES DOWN SYNDROME This condition is also called trisomy 21 and can result from nondisjunction in the sperm or egg Characteristic facial features: • Round face • Flattened nose bridge • Small, irregular teeth • Short stature • Heart defects

  14. The risk of Down syndrome increases dramatically as the age of the mother increases. Why do you think that is?

  15. Klinefelter's syndrome,47, XXY • Results from nondisjunction in egg or sperm • Symptoms: • Language impairment • Female fat distribution (rounded body type) • Less body hair • Low levels of testosterone and small testicles • Infertile

  16. Turner’s Syndrome (X0) Results from nondisjunction in egg or sperm Common symptoms: • Short stature • swelling of the hands and feet • Broad chest and widely spaced nipples • Low hairline • Low-set ears • Reproductive sterility • Increased weight, obesity • Small fingernails • Characteristic facial features • Webbed neck

  17. Edward and Patau Syndromes • Edward, trisomy 18 • Patau, trisomy 13 • Both can result from nondisjunction in sperm or egg • All organ systems affected • Children do not usually live more than a few months

  18. Youtube clip: 99 balloons http://www.youtube.com/watch?v=th6Njr-qkq0

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