Which blood group system does not exhibit dosage effect?

Which blood group system does not exhibit dosage effect?

• A. Kidd
• B. Duffy
• C. Lewis
• D. MNS

Answer: (C)

Dosage effect describes how antigen density on red cells changes with gene copies—homozygous usually gives stronger expression than heterozygous. The Lewis system is different: its antigens aren’t built into the red cell’s membrane by a single gene dose. Instead, Lewis antigens are produced in body fluids and then adsorbed onto red cells, with expression driven mainly by secretor status and the activity of fucosyltransferases, not by how many copies of a Lewis gene are present. That means antigen density on red cells doesn’t reliably increase with gene dosage, so it doesn’t show a true dosage effect. Other systems like Kidd, Duffy, and MNS have antigen expression that varies with zygosity, showing the dose-dependent pattern.

Dosage effect describes how antigen density on red cells changes with gene copies—homozygous usually gives stronger expression than heterozygous. The Lewis system is different: its antigens aren’t built into the red cell’s membrane by a single gene dose. Instead, Lewis antigens are produced in body fluids and then adsorbed onto red cells, with expression driven mainly by secretor status and the activity of fucosyltransferases, not by how many copies of a Lewis gene are present. That means antigen density on red cells doesn’t reliably increase with gene dosage, so it doesn’t show a true dosage effect. Other systems like Kidd, Duffy, and MNS have antigen expression that varies with zygosity, showing the dose-dependent pattern.