What genetic condition requires a homozygous dominant genotype for its occurrence?

Sickle cell anemia is a genetic condition that results from a homozygous recessive genotype (having two copies of the sickle cell allele) rather than a homozygous dominant genotype. For the occurrence of cystic fibrosis, an individual must possess a homozygous recessive genotype as well, which means that having two normal alleles would not result in the condition. Huntington's disease, on the other hand, has a dominant inheritance pattern, so only a single copy of the Huntington allele is required for the disease to manifest.

Down syndrome is caused by chromosomal abnormalities, specifically trisomy 21, rather than a specific genotype related to dominant or recessive alleles. It occurs when an individual has three copies of chromosome 21 instead of the normal two, which is unrelated to a traditional homozygous dominant or recessive genotype scenario.

Therefore, the question regarding which genetic condition requires a homozygous dominant genotype is misleading as none of the listed conditions do so.