Question

question 47

synthesis of \\(\text{le}^b\\) substance is only possible with the inheritance of which genes?

fut-1 (h), fut-2 (se), fut-3 (le)
fut-1 (h), o/o, fut-3 (le)
fut-1 (h), a/b, rhag
fut-1 (h), fut-2 (se)

Explanation:

Understand the target substance

The question asks for the genes required to synthesize the \(\text{Le}^\text{b}\) substance.

Analyze the biosynthetic pathway

Using the Lewis Antigen Biosynthesis knowledge point

• The precursor substance (Type 1 chain) is converted to \(\text{Le}^\text{a}\) by the addition of fucose via the fucosyltransferase enzyme encoded by the Le gene (FUT-3).
• To produce \(\text{Le}^\text{b}\), the Type 1 precursor must first be modified by the fucosyltransferase encoded by the Se gene (FUT-2) to form Type 1 H substance.
• The Le gene (FUT-3) then adds fucose to this Type 1 H substance to create the \(\text{Le}^\text{b}\) antigen.
• Additionally, the H gene (FUT-1) is responsible for synthesizing H substance on Type 2 chains (red blood cells), which is essential for normal ABH expression.
• Therefore, synthesis of \(\text{Le}^\text{b}\) requires the functional inheritance of FUT-1 (\(H\)), FUT-2 (\(Se\)), and FUT-3 (\(Le\)).

Evaluate the options

Using the Lewis Blood Group knowledge point

• Option 1: FUT-1 (H), FUT-2 (Se), FUT-3 (Le) — This contains all three necessary genes.
• Option 2: FUT-1 (H), O/O, FUT-3 (Le) — Lacks the Se gene (FUT-2), which would result in \(\text{Le}^\text{a}\) synthesis only.
• Option 3: FUT-1 (H), A/B, RHAG — Lacks both Se and Le genes.
• Option 4: FUT-1 (H), FUT-2 (Se) — Lacks the Le gene (FUT-3), resulting in the \(\text{Le(a-b-)}\) phenotype.

Answer:

• (A) FUT-1 (H), FUT-2 (Se), FUT-3 (Le) (Correct answer)
• (B) FUT-1 (H), O/O, FUT-3 (Le)
• (C) FUT-1 (H), A/B, RHAG
• (D) FUT-1 (H), FUT-2 (Se)