Confusing SAT 2 bio question?

Archive SAT Subject Test Preparation
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<p>In pea plants, two separate alleles code for the shape and color of peas. Round shape is dominant over wrinkled, and green color is dominant over yellow. In a controlled experiment, a plant with round green peas is crossed with a plant with wrinkled yellow peas.</p>

<p>F1 plants=13 plants with round green peas. </p>

<p>If a cross of F1 plants produces 31 plants in the F2 generation, approximately how many should have wrinkled green peas?</p>

<p>A.0
B.3
C.6
D.10
E.15</p>

<p>Answer was C</p>

<p>My question is how is this problem answerable if the specific genotype of the peas are not stated? The recessive genotype can only be rrgg (wrinkled yellow) but the round green pea can be RrGg RRGG RRGg or RrGG. Crossing either of these four would result in completely different results wouldn’t it?</p>

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<p>“In a controlled experiment, a plant with round green peas is crossed with a plant with wrinkled yellow peas.”
The specific genotype IS stated, in that sentence. The cross is RRGG x rrgg. The round green peas in the P generation HAVE to be RRGG because when crossed the offspring are 100% round green peas, so they’re all RrGg. So the F1 cross is RrGg x RrGg.</p>

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<p>IntrnetHteMchne is correct, but another important piece of information is that it says “F1 plants=13 plants with round green peas.” That’s how it’s known that 100% of the peas are round and green.</p>

<p>Therefore, RRGG x rrgg = 100% RrGg (Round Green)</p>