Which condition is commonly known as a sex-linked genetic disorder?

Hemophilia is recognized as a sex-linked genetic disorder, specifically linked to the X chromosome. This means that the genes responsible for hemophilia are located on the X chromosome, which affects the way the disorder is inherited. Males, who have one X and one Y chromosome, are more commonly affected because they only inherit one copy of the X chromosome. If that chromosome carries the mutated gene for hemophilia, they will express the disorder. In contrast, females have two X chromosomes, so if they inherit one mutated gene, they may be carriers without necessarily expressing the disease unless they inherit the mutated gene from both parents.

The other conditions listed, while they are serious genetic disorders, are not classified as sex-linked. Sickle cell anemia is an autosomal recessive disorder, meaning it can affect both males and females equally and is carried on a non-sex chromosome. Cystic fibrosis is also an autosomal recessive disorder, and Marfan syndrome is an autosomal dominant connective tissue disorder. Thus, their inheritance patterns differ significantly from that of hemophilia, which is why hemophilia stands out as the correct choice in the context of sex-linked disorders.