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.