In pea plants, the yellow-seed trait is dominant over green. What colour will appear in the first generation if pure yellow and pure green plants are crossed?

Correct answer: Yellow

Use Mendel’s dominance principle. Let Y represent the dominant yellow allele and y represent the recessive green allele. Pure yellow has genotype YY, while pure green has genotype yy. Their cross is YY × yy, so every offspring receives Y from the first parent and y from the second, giving genotype Yy. Because Y is dominant, all first-generation seeds will appear yellow. Therefore option A is correct.