Context: This passage describes the Marfan syndrome trait in humans:

In a group of humans, some individuals have Marfan syndrome and others do not. In this group, the gene for the Marfan syndrome trait has two alleles. The allele M is for having Marfan syndrome, and the allele m is for not having Marfan syndrome.
Sarah, a human from this group, has Marfan syndrome. Sarah has two alleles for having Marfan syndrome.
Based on this information, what is Sarah's genotype for the Marfan syndrome gene?
A. having Marfan syndrome
B. MM
Identify the correct option from the choices provided and respond with the letter of the correct option.

B