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Released STAAR Biology EOC · 2026 · Item 20 · 1 point

Walkthrough: Biology 2026, Item 20

B.8B · Genetic Crosses · unscored study

A gardener is growing sunflowers, which have an incomplete dominance inheritance pattern. The sunflowers can produce red, orange, and yellow flowers. The gardener crosses a red sunflower with the genotype RRRR with a yellow sunflower with the genotype rrrr. Which outcome is the MOST LIKELY result of this cross?

  1. One-quarter of the sunflowers will be yellow.
  2. Half the sunflowers will be red.
  3. Three-fourths of the sunflowers will have both red and yellow petals.
  4. All the sunflowers will be orange.

1. Understand the question

The cross is RR×rrRR \times rr with incomplete dominance. Incomplete dominance blends traits, so RrRr plants are orange.

Try the question on your own first, then reveal one step at a time.

2. Solve it step by step

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