Which Lewis genotype results in the phenotype Le(a+b-)?

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Multiple Choice

Which Lewis genotype results in the phenotype Le(a+b-)?

The Lewis phenotype on red cells depends on two genes: FUT3 (the Le gene) and FUT2 (the Se gene), with H antigen status also influencing Lewis expression. Le(a+b-) means Lea is present but Leb is absent. You need a functional FUT3 to produce Lea, so the Le allele must be present (LeLe or Lele). Leb formation requires a secretor (Se) and the H antigen as a substrate; however, if the person is Bombay (hh), the H antigen is absent, so Leb cannot be formed regardless of secretor status. Therefore, a genotype with LeLe and hh will yield Lea on the cells but no Leb, giving Le(a+b-). The SeSe part is compatible because secretor status doesn’t reintroduce Leb when H is missing.

The Lewis phenotype on red cells depends on two genes: FUT3 (the Le gene) and FUT2 (the Se gene), with H antigen status also influencing Lewis expression. Le(a+b-) means Lea is present but Leb is absent. You need a functional FUT3 to produce Lea, so the Le allele must be present (LeLe or Lele). Leb formation requires a secretor (Se) and the H antigen as a substrate; however, if the person is Bombay (hh), the H antigen is absent, so Leb cannot be formed regardless of secretor status. Therefore, a genotype with LeLe and hh will yield Lea on the cells but no Leb, giving Le(a+b-). The SeSe part is compatible because secretor status doesn’t reintroduce Leb when H is missing.

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