[Campbell Biology P.329] Tay-Sachs disease is an inherited disorder. At the organismal level... | Practice Question

Tay-Sachs disease is an inherited disorder. At the organismal level, the Tay-Sachs allele is considered recessive. However, at the biochemical level, the activity level of the lipid-metabolizing enzyme in heterozygotes is intermediate. At the molecular level, the normal allele and the Tay-Sachs allele are codominant. This example illustrates that the observed dominant/recessive relationship of alleles depends on what?

  • A: The specific gene being studied.
  • B: The level at which the phenotype is analyzed.
  • C: Whether the allele is dominant or recessive.
  • D: The frequency of the dominant allele in the population.

Explanation

The text explicitly states: 'As you can see, whether alleles appear to be completely dominant, incompletely dominant, or codominant depends on the level at which the phenotype is analyzed.' The Tay-Sachs example clearly demonstrates this.