1. Non-disjunction

2. Non-disjunction
Non-disjunction means that chromosomes fail to separate correctly when gametes are formed.
Because of this, a sperm or egg cell may have two copies of a chromosomes or no copies of a chromosome.

3. Disorders caused by non-disjunction
Down syndrome
Patau syndrome
Edward Syndrome
Turner Syndrome
Klinefelter Syndrome

4. Down Syndrome Trisomy 21 – 3 copies of chromsome 21
Causes cognitive impairment, facial abnormalities, heart defects and stomach problems

5. Patau Syndrome Trisomy 13 – 3 copies of chromsome 13
Causes major heart and brain damage along with deformities of the hands and feet.
90% of affected individuals die within a year after birth.

6. Edward Syndrome Trisomy 18 – 3 copies of chromosome 18
Causes major heart, kidney and brain deformities
50% die before 2 months of age.
90% die before 12 months of age.

7. Turner Syndrome Monosomy X – female with one X chromosome
Normal life expectancy
Can cause mild kidney problem, short height, webbed neck and sterility.

8. Klinefelter Syndrome Males with XXY genotype
1 out of 500 males have the condition but show no symptoms
Creates reduced fertility