Worked example
A model animal with genotype Bb is crossed with bb. The first parent contributes B or b with equal probability; the second contributes b. The offspring are expected to be half Bb and half bb. Under complete dominance, half are expected to show the dominant feature.
Contrast and common error
A dominant-looking offspring can still carry the recessive allele. An expected fraction also does not set a family quota. If births are independent, previous offspring do not consume dominant or recessive outcomes. Other inheritance models may have different phenotype rules.
Transfer check
Under complete dominance, a Dd parent is crossed with DD. What fraction is expected to carry d, and what fraction shows the recessive phenotype? Check: half carry d as Dd. None are dd in this cross.
Try it, then explain it.
Complete a short set without looking at the example. After each answer, explain which evidence or rule supports your decision and why the alternatives do not fit.
Sources & authorship
Original OpenExam explanations and examples. References support the concepts; they are not the source of copied questions. Independent educator review is pending.
OpenStax Biology 2e 12.3 Laws of Inheritance