For a person to develop Huntington's disease, he must be homozygous (HH) or heterozygous (Hh) for the dominant allele.
Huntington’s disease is a type of defective dominant disease. This means that any person having 1 or 2 defective dominant genes, have the disorder. But, if a person has 2 recessive genes, they are normal.
Mom (Hh) x Dad (Hh)
H h
H HH Hh
h Hh hh
Cystic fibrosis is a type of a recessive disease i.e., a person having 1 or 2 dominant genes is normal. But a person having 2 mutated recessive genes are diseased.
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