Yellow-seeded pea plants may be homozygous or heterozygous. To find out which, we can cross the plants with:

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Crossing yellow-seeded pea plants with true-breeding green-seeded plants will reveal whether the yellow-seeded plants are homozygous or heterozygous. If the yellow-seeded plants are homozygous, then all offspring will be yellow-seeded. However, if the yellow-seeded plants are heterozygous, then half the offspring will be yellow-seeded and half will be green-seeded. It is not necessary to cross with true-breeding yellow-seeded plants (choice A) because that would not reveal whether the yellow-seeded plants being tested are homozygous or heterozygous. Similarly, crossing with heterozygous green-seeded plants (choice C) would not give clear results. Crossing with the same genotype (choice E) would not produce any new information.

Yellow-Seeded Pea Plants May Be Homozygous or Heterozygous