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A round yellow plant is crossed with rryy.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A round yellow plant is crossed with rryy. The seeds are round yellow and round green, half and half, with no wrinkled seeds. Which of RRYY, RRYy, RrYY and RrYy is the plant? Explain with its gametes.
Need a reminder? The key ideaShow
With two genes, product("Rr", "Yy") gives the four gametes RY, Ry, rY and ry. Four gametes meet four in 16 boxes; each gene of the child is sorted on its own. RrYy with RrYy gives 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green. A test cross with rryy shows the hidden letters of a dominant-looking plant.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Shape. All seeds are round, so the plant never passes on r. It is RR.
Step 2. Colour. Half the seeds are green, so the plant passes on y half the time. It is Yy.
Step 3. The gametes. RRYy makes RY and Ry equally. Each meets ry from the rryy parent, giving RrYy (round yellow) and Rryy (round green).
Answer: RRYy.
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