Most genetic diseases are caused by recessive alleles. Why?

Answer: Recessive allele is the allele that is not manifested in the individual like the dorminant allele unless the person inherited two copies. In the case of genetic diseases, the individual inherited two recessive alleles that are mutated. The mutation of the two recessive alleles cause genetic diseases. The problems in the recessive alleles cause aberrations in the expression of the genes.

Explanation:

Genetic diseases are inherited disorder which is caused by mutation of genes which caused aberrations in the Gene expression.