Suppose that Mendel did a cross between plants that varied in the color of the f

Question

Suppose that Mendel did a cross between plants that varied in the color of the flowers of the pea plants. Some were purple and some were white. He first created true breeding lines of the two forms. He then crossed them to form the first offspring generation which were all purple and had the genotype Pw. What would happen if he back-crossed Pw and the original true-breeding white line? Provide both the genotype and phenotype ratios of this cross. You must label your answers, explicitly stating what the genotype and phenotype ratios are.

Explanation / Answer

If the F1 offsprings have genotype Pw and all are purple, then purple color (P) is dominant over white (w). Since the parents were true breeders, the white parent should have genotype ww.

Back-cross between Pw and true-breeding white (ww) lines-

Cross = Pw x ww

gametes will be (P, w) and (w), which cross to form (Pw, purple) and (ww, white). Thus, 50% of them will be purple and 50% white. Phenotypic ratio is purple:white = 1:1, and the genotypic ratio is Pw:ww = 1:1

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