4.4 Abnormal Meiosis: Nondisjunction
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Transcript of 4.4 Abnormal Meiosis: Nondisjunction
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4.4 Abnormal Meiosis: Nondisjunction
Pages 116-120
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Problem
Problems with meiosis may lead to genetic disorders or infertility.
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Contributing Factors
• Disease• Environmental factors• Random errors
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Non-disjunction
Homologous chromosomes fail to separate during meiosis.
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One daughter cell has one extra chromosome. One daughter cell has one missing chromosome
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Too much or too little protein is made.
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trisomy
3 copies of a chromosomeExamples: trisomy 21-Down’s syndrome
trisomy 13-Patau’s syndrome
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monosomy
1 copy of a chromosomeExample: 0X -Turner’s syndrome
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Risk Factors Increase with Age
The risk of non-disjunction increases with age.1 in 800 children is born with Down Syndrome.
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• A woman in her 20’s has a 1 in 1000 chance of delivering a child with Down Syndrome.
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• A woman in her 40’s has a 1 in 40 chance of delivering a child with Down Syndrome
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Karyotype
Prepared using white blood cells frozen in metaphase, photographed and sorted
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Prenatal Testing
After age 35.At 8 weeks, the chorionic villus sampling (CVS) can remove cells from the outer membrane surrounding the embryoLater, amniocentesis can be doneBetween 15-20 weeks a multiple markerblood test can be done.
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Infertility
10% of couples in Ontario are unable to produce children
-poor sperm or egg quality-blockages in the fallopian tube or vas deferens
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Assisted Reproductive Technology
-increased gamete production-fertility drugs-in vitro fertilization
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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
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Intracytoplasmic sperm injection
ICSIOne sperm is inserted into the egg
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Laser-assisted Hatching
Using a laser, a whole is made in the zona pellucida, the outer shell of a fertilized egg, allowing the embryo to hatch and implant in the uterus.
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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
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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.