In the Beadle and Tatum study, it was important that Neurospora was haploid because:

A) it is easier to grow haploid molds in the laboratory.
B) haploid molds have simpler nutritional requirements than do diploid molds.
C) a mutation that arises is not masked by a normal allele on a homologous chromosome.
D) haploid Neurospora will always mutate.
E) diploid Neurospora will always mutate.

In haploid organisms, any mutation that occurs in a gene will be expressed in the phenotype because there is no corresponding allele on a homologous chromosome to mask its effect. This characteristic was crucial for Beadle and Tatum's experiments to directly link mutations in specific genes to deficiencies in metabolic pathways, as each mutation led to a loss of function that could be observed without the complication of a second, potentially normal allele hiding the mutation's effects.