Sometimes, when Mendel crossed two pea plants with each other, he obtained a phenotypic ratio of 3:1 purple-flowered pea plants to white-flowered pea plants. These results are consistent with which set of parents?

Question

A.  homozygous purple pea plant and homozygous white pea plant
B.  heterozygous purple pea plant and homozygous white pea plant
C.  heterozygous purple pea plant and homozygous purple pea plant
D.  heterozygous purple pea plant and heterozygous purple pea plant

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain?

Gather Content
· What do you already know about crosses and phenotype ratios? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

D.  heterozygous purple pea plant and heterozygous purple pea plant

Clarify Question
· What is the key concept addressed by the question?
        o Instead of asking you to derive the phenotype ratio from the cross, here the question asks you to determine which genotypes could be crossed to produce a certain phenotypic ratio.
· What type of thinking is required?
        o You have to use your understanding of monohybrid crosses and Apply it to this scenario of a 3:1 ratio of purple:white flowers.
· What key words does the question contain?
        o The phenotypic ratio is a the ratio of phenotypes – the physical traits. Remember that a certain phenotype, like purple flowers, may result from more than one genotype.

Gather Content
· What do you already know about crosses and phenotype ratios? How does it relate to the question?
        o Punnett squares are very helpful for determining phenotype ratios. A pen and paper might be helpful.
        o Don’t forget that purple (P) is dominant over white (p).

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o If you don’t know the answer right away, look at the answer choices. Could you determine the phenotypic ratios that would result from each choice, to find the one that matches 3:1 purple:white?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Look at the answer choices. For each, you will need to translate the words (“homozygous purple”) into the genotype (“PP”). What phenotypes result from each of these crosses?
        o Recall that P is dominant for the purple phenotype. So a cross of homozygous purple (PP) x homozygous white (pp) will produce only Pp purple offspring.
        o Recall that gametes receive one allele randomly in equal amounts. So a cross of heterozygous purple (Pp) x homozygous white (pp) will produce half purple (Pp) offspring and half white (pp) offspring.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question required you to If you didn’t write out the Punnett square, you may have decided that Pp x Pp produces just three types of offspring: PP, Pp, and pp. Don’t forget that there are two categories of Pp offspring: P (maternal) p (paternal) and p (maternal) P (paternal). So three of the four combinations are purple, producing a 3:1 ratio. your knowledge and understanding to this unfamiliar situation.
        o Even if you didn’t remember that monohybrid crosses produce a 3:1 ratio, you could solve the problem by considering each of the answer choices.
        o If you didn’t write out the Punnett square, you may have decided that Pp x Pp produces just three types of offspring: PP, Pp, and pp. Don’t forget that there are two categories of Pp offspring: P (maternal) p (paternal) and p (maternal) P (paternal). So three of the four combinations are purple, producing a 3:1 ratio.