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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. . - PowerPoint PPT Presentation
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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.
One daughter cell has one extra chromosome. One daughter cell has one missing chromosome
Too much or too little protein is made.
trisomy
3 copies of a chromosomeExamples: trisomy 21-Down’s syndrome
trisomy 13-Patau’s syndrome
monosomy
1 copy of a chromosomeExample: 0X -Turner’s syndrome
Risk Factors Increase with Age
The risk of non-disjunction increases with age.1 in 800 children is born with Down Syndrome.
• A woman in her 20’s has a 1 in 1000 chance of delivering a child with Down Syndrome.
• A woman in her 40’s has a 1 in 40 chance of delivering a child with Down Syndrome
Karyotype
Prepared using white blood cells frozen in metaphase, photographed and sorted
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.
Infertility
10% of couples in Ontario are unable to produce children
-poor sperm or egg quality-blockages in the fallopian tube or vas deferens
Assisted Reproductive Technology
-increased gamete production-fertility drugs-in vitro fertilization
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
Intracytoplasmic sperm injection
ICSIOne sperm is inserted into the egg
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.
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
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.