Lithuanian University of Health Sciences (LSMU) Entrance Practice exam

Vitamin D resistance is indeed an example of an X-linked dominant disorder. This condition arises from mutations in the gene that is located on the X chromosome, which affects the body's ability to use vitamin D effectively. Because the disorder is dominant, only one copy of the mutated gene is needed for the condition to manifest in both males and females.

In X-linked dominant disorders, affected males can pass the condition on to all of their daughters but none of their sons, while affected females can pass the condition to both daughters and sons, resulting in a pattern of inheritance that can be observed in multiple generations.

Cystic fibrosis, color blindness, and Tay-Sachs disease are caused by different modes of genetic inheritance. Cystic fibrosis is an autosomal recessive disorder, requiring two copies of the mutated gene for the disease to develop. Color blindness is typically an X-linked recessive trait, where males are more commonly affected, and females can be carriers without showing symptoms. Tay-Sachs is also an autosomal recessive disorder, primarily affecting individuals of certain ethnic backgrounds and requiring two copies of the recessive allele for the disease to manifest.