Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Mendel's RrYy with RrYy cross gave round yellow, round green, wrinkled yellow and wrinkled green seeds, in all. How many round yellow and how many wrinkled green seeds does the 9:3:3:1 ratio expect?
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.
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. One part. seeds.
Step 2. Round yellow. seeds; Mendel saw .
Step 3. Wrinkled green. seeds; Mendel saw .
Answer: round yellow and wrinkled green expected. The real counts are close.
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