which of the following describes the expression of the tay-sachs allele in humans at the biochemical level?

The Tay-Sachs allele expresses incompletely at the biochemical level in humans. Specifically, individuals who are homozygous for HEXA mutations have little to no hexosaminidase A (Hex A) activity, leading to GM2 ganglioside accumulation in neurons and the Tay-Sachs phenotype. Carriers (heterozygotes) typically have intermediate Hex A activity, higher than affected individuals but lower than non-carriers, which explains why the inheritance appears recessive at the organism level yet shows a graded biochemical effect. This incomplete dominance means the enzyme activity levels in heterozygotes are intermediate, not simply “normal” or “deficient,” reflecting the continued impact of a single mutant allele on Hex A function.