What describes strict dominant-recessive inheritance?

• A. Dominant allele is sometimes expressed
• B. Dominant allele is always expressed in the phenotype
• C. Recessive allele is always expressed
• D. Genotype determines phenotype

Answer: (B)

Complete dominance means a single copy of the dominant allele is enough to produce the dominant phenotype, and a heterozygote looks the same as a homozygous dominant. That’s why describing the dominant allele as always expressed in the phenotype best captures strict dominant–recessive inheritance: whenever the dominant allele is present, its trait appears. For example, with alleles D and d, individuals with DD or Dd show the dominant trait, while dd shows the recessive trait. Saying the dominant allele is sometimes expressed would fit patterns like incomplete dominance or variable expressivity, not strict dominance. Saying the recessive allele is always expressed describes a different pattern, not complete dominance. And while genotype influences phenotype, the key point here is that the presence of a single dominant allele reliably yields the dominant phenotype.