Which pair illustrates allotypic variation within the same subclass?

Which pair illustrates allotypic variation within the same subclass?

• A. IgM1 and IgM2
• B. IgG1 and IgG2
• C. IgA1 and IgA2
• D. IgG1m3 and IgG1m17

Answer: (D)

Allotypic variation arises from inherited differences in the constant region of the same antibody class and subclass. The two antibodies shown are both IgG1, so they share the same subclass, but they carry different allotypic determinants on the gamma-1 heavy chain (G1m3 vs G1m17). That exact combination—same subclass, different constant-region alleles—illustrates allotypic variation within one subclass. The other options pair different subclasses (IgG1 vs IgG2, IgA1 vs IgA2) or aren’t the classic within-subclass allotype examples, so they don’t demonstrate within-subclass allotypy as clearly.

Allotypic variation arises from inherited differences in the constant region of the same antibody class and subclass. The two antibodies shown are both IgG1, so they share the same subclass, but they carry different allotypic determinants on the gamma-1 heavy chain (G1m3 vs G1m17). That exact combination—same subclass, different constant-region alleles—illustrates allotypic variation within one subclass. The other options pair different subclasses (IgG1 vs IgG2, IgA1 vs IgA2) or aren’t the classic within-subclass allotype examples, so they don’t demonstrate within-subclass allotypy as clearly.