When%20Meiosis%20Goes%20Wrong:

1
When Meiosis Goes Wrong

• Non-Disjunction

2
Normal Meiosis

• In Anaphase I, homologous chromosomes split up
  and each one goes to a pole.
• In Anaphase II, the chromosome break in two and
  each chromatid goes to a pole.

3
Non-Disjunction
Nondisjunction of homologous chromosomes in
meiosis I

• Sometimes, in Anaphase I, the chromosome pairs
  DONT split
• 2 cells with an extra chromosome, 2 missing a
  chromosome
• In Anaphase II, if a chromosome doesnt split in
  two
• 2 normal cells, 1 with too many chromosomes, 1
  with not enough.

4
So?

• When non-disjunction happens, the egg or the
  sperm produced has the wrong number of
  chromosomes.
• If this egg/sperm fertilizes, the baby will have
  the wrong number of chromosomes.
• This child often suffers from health problems and
  learning disabilities.

5
To Diagnose Non-Disjunction
Normal Male

• Doctors use a karyotype chart, which shows all
  your chromosomes.
• A normal karyotype has 46 chromosomes (23
  pairs)
• Males have an X and a Y, females have 2 X
  chromosomes.

Normal Female
6
Examples of Disorders

• Downs Syndrome
• 3 copies of chromosome number 21
• Heart defects, poor mouth development, learning
  disabilities
• Shortened life expectancy

7
Examples of Disorders

• Trisomy 13
• 3 copies of chromosome number 13.
• Major learning disabilities, small head, mouth
  deformities
• Few survive to adulthood

8
Examples of Disorders

• Turners Syndrome
• Only 1 copy of the X chromosome.
• Short, female, webbed neck, infertile, heart
  defects.
• Normal life expectancy and intelligence.