Human Abnormalities and Nondisjunction

Nondisjunction: homologous chromosomes/chromatids fail to separate during meiosis
Since it happens to a sperm or egg, the new baby can end up with 3 copies of a chromosome = trisomy or only one copy of a chromosome = monosomy

Down syndrome = trisomy 21
- 1 in 800 births
- Similar facial features
- Slanted eyes
- Protruding tongue
- Simian line on palm
- Most common chromosomal abnormality
- 50% have heart defects that need surgery to repair
- Mild to severe mental retardation
- Increases susceptibility to many diseases
- Risk of having a child with Down syndrome increases with age of mom
- Risk of having a child with Down syndrome related to age of mom
- More common in women UNDER 16 or OVER 35
Turner Syndrome = XO
- 1 in 5000 births
- Females have only one X chromosome
- Small size
- Slightly decreased intelligence
- 35% have heart abnormalities
- Hearing loss common
- Broad chest
- Reproductive organs don’t develop at puberty
- Can’t have children
Klinefelter Syndrome = XXY
- 1 in 1000 births
- Males have extra X chromosome (XXY)
- Can have more than 2 X’s
- Feminized characteristics
- 20% slight breast development
- Less facial/body hair after puberty
- Average/slight decrease in intelligence
- Small testes/can’t have children
- Usually not discovered until puberty; when don’t mature like peers