Mutations

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

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

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

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

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

Cri-du-chat syndrome

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.

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

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

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

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

Edward Syndrome Chromosome Abnormality: Extra chromosome (number 18)

Edward Syndrome