Same Allele, Different Locus, Different Phenotype
Different mutations in the same gene can result in different phenotypes. A good example is the RET proto-oncogene. Germline mutations of RET lead to multiple endocrine neoplasia (MEN) type 2. The disease produced varies depending on where in the RET gene the germline mutation sits, so the phenotype may be MEN-2A, MEN-2B, or familial medullary thyroid cancer.