Final answer:
Rett syndrome is generally observed in females because it is lethal in males, who have only one X chromosome. Females have two X chromosomes, which allows them to survive with the disorder when only one of the chromosomes carries the mutated gene.
Step-by-step explanation:
Rett syndrome is typically only seen in females because it is an X-linked disorder. Males have only one X chromosome, so if they inherit a gene with Rett syndrome, it is usually lethal, meaning they do not survive. Females, on the other hand, have two X chromosomes, allowing them to survive with one normal and one mutated gene. The presence of two X chromosomes in females means that even if one X chromosome carries the Rett syndrome mutation, they may still have a functioning gene on their other X chromosome to partially compensate for the disorder.
The correct answer to why Rett syndrome is primarily seen in females is: c) Rett syndrome is lethal in males. This lethality in males means that the presence of the syndrome is usually not observed in them; they either pass away before or shortly after birth. As for females, they have two X chromosomes, allowing for the possibility of being a carrier for Rett syndrome or affected by it depending on whether they inherit one or two mutated genes.