Context: This passage describes the Thomsen disease trait in humans:

In a group of humans, some individuals have Thomsen disease and others do not. In this group, the gene for the Thomsen disease trait has two alleles. The allele for having Thomsen disease (M) is dominant over the allele for not having Thomsen disease (m).
Malia is a human from this group. Malia has the heterozygous genotype Mm for the Thomsen disease gene.
Based on this information, what is Malia's phenotype for the Thomsen disease trait?
A. not having Thomsen disease
B. having Thomsen disease
Identify the correct choice from the options below and respond with the letter of the correct option.

B