For a certain species of flowers, blue petals (P) are dominant to white petals (p)...
For a certain species of flowers, blue petals (P) are dominant to white petals (p) and long stems (Q) are dominant to short stems (q). Flower 1 is the offspring of a purebred long-stemmed, blue flower (PPQQ) and a purebred short-stemmed, white flower (ppqq). If Flower 1 is crossed with a short-stemmed, white flower, what fraction of its offspring will be white and short-stemmed?
- A. 4/16
- B. 2/16
- C. 1/16
- D. 8/16
Correct Answer: A. 4/16
Explanation
Since the offspring receives one allele from each parent, crossing a purebred dominant organism with a purebred recessive organism (PPQQ x ppqq) will always result in a hybridized offspring (PpQq). Thus, Flower 1's genotype is PpQq. Also remember that a recessive phenotype always indicates double recessive alleles for that trait. And so, crossing Flower 1 with a white, short-stemmed flower will result in the cross PpQq x ppqq. The next step is to draw a 4x4 Punnett square, as seen in the diagram. The desired genotype for this question is ppqq (recessive phenotype), and from the Punnett square you will be able to see that 4/16 of the squares will carry this specific genotype.