1. Mutations

2. Down’s syndrome Chromosome Abnormality: Extra Chromosome (number 21)

3. Down’s syndrome Characteristics (phenotype):
Characteristic facial features
Short stature
Heart defects
Susceptibility of respiratory infections
Mental retardation
Most are sexually underdeveloped and sterile

4. Down’s syndrome Incidence per live births: 1 in 700.
Risk rises with increase in maternal age

5. Cri-du-chat syndrome Chromosome abnormality: Deletion of arm of chromosome 5.

6. Cri-du-chat syndrome Characteristics (Phenotype):
Affected infants crying sounds like a cat meowing
Ears are positioned on the low side of the head
Mental retardation

7. Cri-du-chat syndrome

8. Klinefelters Syndrome
Chromosome Abnormality: Extra sex chromosome. Only in males (XXY)
Characteristics (phenotype):
Males are taller than average
Sterile (testes are much smaller than average)
Facial hair is sparse
Breasts may be enlarged
Some show mild mental impairment.

9. Klinefelters Syndrome
Incidence per live births:
1 in 1000, risk increases with maternal age

10. Turner Syndrome
Chromosome Abnormality:Missing sex chromosome. Only in girls. (XO)

11. Turner Syndrome Characteristics (phenotype):
Behaviour is generally normal in childhood
Infertile – do not have functioning ovaries and sex hormones – therefore secondary sex traits are reduced

12. Turner Syndrome Incidence per live births: 1 in 5000
98% of zygotes spontaneously abort

13. Edward Syndrome Chromosome Abnormality: Extra chromosome (number 18)

14. Edward Syndrome