Final answer:
Rett syndrome is mostly seen in females because it's an X-linked dominant disorder. Females have two X chromosomes which allow for some normal function despite one mutated gene, while male embryos with the mutation typically do not survive.
Step-by-step explanation:
Rett syndrome is primarily seen in females because it is a genetic disorder associated with mutations in the MECP2 gene on the X chromosome. For females, who have two X chromosomes, a functional gene on one of the X chromosomes can generally compensate for a mutation in the other. However, males only have one X chromosome, and if they inherit a mutated MECP2 gene, the outcome is usually lethal in early development, which is why Rett syndrome is rare in males. Additionally, due to the process of X inactivation, in which one of the X chromosomes is randomly inactivated in females, some cells may have the normal MECP2 gene active while others do not, allowing for survival but leading to the symptoms of Rett syndrome. This mechanism of X-linked dominant inheritance results in the rare presence of Rett syndrome among females and its scarcity in males.