What disorder is caused by a single dominant allele and results in dwarfism?

Achondroplasia is a genetic disorder caused by a mutation in the FGFR3 gene, which is inherited in an autosomal dominant manner. This means that only one copy of the mutated allele is necessary for an individual to exhibit the characteristics of the disorder. Achondroplasia predominantly results in dwarfism due to the way that this mutation affects bone growth, leading to shorter stature and disproportionate body proportions.

The disorder is characterized specifically by a large head with a prominent forehead, shortened limbs, and overall shorter stature compared to individuals without the condition. This genetic basis explains its classification as a single dominant allele disorder rather than a complex condition with multiple genetic influences.

In contrast, Turner syndrome is a chromosomal disorder affecting females, characterized by the absence of one X chromosome, which leads to various physical and developmental features. Down syndrome, caused by an extra copy of chromosome 21, is a chromosomal condition and not related to single allele dominance. Marfan syndrome is also an autosomal dominant disorder, but it primarily affects connective tissue and results in tall stature, long limbs, and cardiovascular problems, rather than dwarfism. This distinction further emphasizes why achondroplasia is the correct answer regarding dwarfism associated with a single dominant allele.