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4.4 Abnormal Meiosis: Nondisjunction

4.4 Abnormal Meiosis: Nondisjunction. Pages 116-120. Problem. Problems with meiosis may lead to genetic disorders or infertility. Contributing Factors. Disease Environmental factors Random errors. Non-disjunction. Homologous chromosomes fail to separate during meiosis. .

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4.4 Abnormal Meiosis: Nondisjunction

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  1. 4.4 Abnormal Meiosis: Nondisjunction Pages 116-120

  2. Problem Problems with meiosis may lead to genetic disorders or infertility.

  3. Contributing Factors • Disease • Environmental factors • Random errors

  4. Non-disjunction Homologous chromosomes fail to separate during meiosis.

  5. One daughter cell has one extra chromosome. One daughter cell has one missing chromosome

  6. Too much or too little protein is made.

  7. trisomy 3 copies of a chromosome Examples: trisomy 21-Down’s syndrome trisomy 13-Patau’s syndrome

  8. monosomy 1 copy of a chromosome Example: 0X -Turner’s syndrome

  9. Risk Factors Increase with Age The risk of non-disjunction increases with age. 1 in 800 children is born with Down Syndrome.

  10. A woman in her 20’s has a 1 in 1000 chance of delivering a child with Down Syndrome.

  11. A woman in her 40’s has a 1 in 40 chance of delivering a child with Down Syndrome

  12. Karyotype Prepared using white blood cells frozen in metaphase, photographed and sorted

  13. Prenatal Testing After age 35. At 8 weeks, the chorionic villus sampling (CVS) can remove cells from the outer membrane surrounding the embryo Later, amniocentesis can be done Between 15-20 weeks a multiple markerblood test can be done.

  14. Infertility 10% of couples in Ontario are unable to produce children -poor sperm or egg quality -blockages in the fallopian tube or vas deferens

  15. Assisted Reproductive Technology -increased gamete production -fertility drugs -in vitro fertilization

  16. In Vitro Fertilization • Use hormone therapy to stimulate egg production • Harvest eggs • Fertilized with sperm in a petri dish • Embryos are transferred to the womb

  17. Intracytoplasmic sperm injection ICSI One sperm is inserted into the egg

  18. Laser-assisted Hatching Using a laser, a whole is made in the zonapellucida, the outer shell of a fertilized egg, allowing the embryo to hatch and implant in the uterus.

  19. Artificial Insemination Semen is placed into the reproductive tract of a female. -breeding of prized animals (race horses, dairy cows) -efforts to save endangered species

  20. Advantages of AI • Less costly than transporting animals • Animals that will not breed in captivity can still reproduce • Sperm can be frozen for a long time • Banks of sperm can be maintained Disadvantage: Belief that it is more important for animals to breed in the wild.

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