Disease Due to Defective Gene On Sex-Chromosomes

Disease due to defective gene on sex-chromosomes

Male are affected since they carry only one X-chromosome while Y-chromosome does not carry its allele. (male-hemizygous).
Females affected only in homozygous condition while the heterozygous are only carrier, since the normal allele is dominant.

Recessive traits:

• Haemophilia (Bleeder’s disease)
• Colour blindness
• Muscular dystrophy (degeneration of muscle)

Dominant traits

• A special type of dwarfism
•  Polydactyly-more number of fingers or toes.
• Wearing off of tooth enamel.
• Huntington's chorea.

Late age 45-50 years syndrome only after 25 years of age causing.

Nerve and muscle.