Step 1: Recall the rule for Rh genotype naming.
In this notation, a capital D means the dominant, antigen-producing allele is present, and a lowercase d means only the non-antigen version is present.
Step 2: Apply the rule: Rh positive needs a capital D.
Any genotype carrying a capital D will make D antigen and will be Rh positive. Only a genotype with no capital D anywhere makes no D antigen and stays Rh negative.
Step 3: Scan each option for a capital D.
Genotypes written as Ccd, CdC, and CDE each carry an uppercase D letter or a mix that points to dominant expression being present.
Step 4: Identify the one genotype with only lowercase d.
CdE carries a lowercase d, not a capital D, alongside the C and E antigen genes, meaning no D antigen protein is being made at all.
Final Answer:
Since CdE has no capital D allele, it produces the Rh negative phenotype, option (4).