IAE Academy

GATE 2019 BT Q.30: solution and answer

GATE 2019 · BTQ.30 · 2 marks · MCQ

Which one of the following is coded by the ABO blood group locus in the human genome?

  1. (A)

    Acyl transferase

  2. (B)

    Galactosyltransferase

  3. (C)

    Transposase

  4. (D)

    β-Galactosidase

See the question in the paper
GATE 2019 BT question 30Tap to open full size

Answer and solution

ANSWER

The ABO blood-group locus is coded by (B) Galactosyltransferase.

Official answer: BSource: Official answer key, GATE 2019 BT (IIT Madras)

  1. The ABO locus encodes an enzyme that transfers a sugar residue onto the H antigen precursor displayed on red blood cell surfaces, converting it into the A or B antigen.

  2. The A allele's product adds N-acetylgalactosamine to the H antigen; the B allele's product adds galactose. Both are sugar-transferring enzymes of the glycosyltransferase family, which the question's options label as "galactosyltransferase."

  3. Option (A) Acyl transferase — wrong; these enzymes transfer acyl groups (e.g., in lipid or acetylation chemistry) and have no role in ABO antigen formation.

  4. Option (B) Galactosyltransferase — correct; the ABO locus encodes a glycosyltransferase-type enzyme that adds a sugar residue to the H antigen, which is exactly the product of this locus.

  5. Option (C) Transposase — wrong; transposases move transposable elements within the genome and are unrelated to antigen biosynthesis.

  6. Option (D) β-Galactosidase — wrong; this is a hydrolase that cleaves a terminal galactose (e.g., in lactose breakdown), the reverse reaction of a sugar-adding transferase.

  7. By elimination and by the known biochemistry of the ABO locus product, the correct choice is (B) Galactosyltransferase.

KEY IDEA

The ABO locus encodes a glycosyltransferase enzyme that attaches a terminal sugar residue onto the H antigen precursor on the red blood cell surface, generating the A or B antigen; this class of enzyme is grouped under "galactosyltransferase."

WATCH OUT FOR

Confusing this transferase (which ADDS a sugar to build the antigen) with β-galactosidase, a hydrolase that REMOVES/cleaves a sugar (as in the lacZ system) — the two enzyme classes catalyze opposite reactions and are easy to swap under time pressure.

From the GATE 2019 BT paper. Every question of this paper · Download the full paper · All 10 Mendelian genetics questions, with notes

More Mendelian genetics questions