Since Asha is a healthy woman in her forties, she does not have Niemann-Pick disease type A.
For this question , assume that she is a healthy person who is a carrier. If Asha is a carrier of the allele of Niemann-Pick disease type A what is her genotype?
By the definition of "carrier," Asha does not exhibit any physical features (phenotype) of the Nieman-Pick disease, but she carries an allele for this disease. In order for this to be possible, Asha must carry a autosomal dominant allele for this gene to mask the effects of carrying an allele for the Nieman-Pick disease, which is an autosomal recessive allele. Therefore, if we label the alleles for this gene as "A" (dominant) and "a" (recessive), Asha's genotype should be:
The dominant allele, A, ensures that Asha does not exhibit any physical features of this disorder even though she does carry the allele for this disorder (but it is recessive so it is masked by the dominant allele).
In order for somebody to exhibit the physical effects of this disorder, they must have the genotype of "aa." This prevents any masking of the effects of this autosomal recessive allele, which codes for the Nieman-Pick disease type A.