For ten points, identify this sex chromosome, two of which are possessed by females.
The similarity of this structure between mice and humans supports Ohno's law about the conservation of these structures in mammals. A mutation in the FMR1 gene results in a small constricted band on the bottom of this structure, which makes it appear easily breakable. The gene XIST produces RNA to silence it, and to avoid a double dosage, one of these structures is inactivated via lyonization and becomes a (*) Barr body. Turner syndrome is caused by a missing one of these chromosomes, and diseases linked to it, like hemophilia and color blindness, are more common in males. For ten points, identify this sex chromosome, two of which are possessed by females.
The similarity of this structure between mice and humans supports Ohno's law about the conservation of these structures in mammals.
X chromosome [accept just X after "chromosome" is read; prompt on "chromosome" until mentioned]