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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. .
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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
trisomy 3 copies of a chromosome Examples: trisomy 21-Down’s syndrome trisomy 13-Patau’s syndrome
monosomy 1 copy of a chromosome Example: 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 embryo Later, amniocentesis can be done Between 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 ICSI One sperm is inserted into the egg
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.
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.