In the F2 of a dihybrid cross, round green and wrinkled yellow seeds appear.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In the F2 of a dihybrid cross, round green and wrinkled yellow seeds appear. Neither parent had them. How do these seeds show that seed shape and seed colour are inherited independently?
Need a reminder? The key ideaShow
In a dihybrid cross, pure round yellow (RRYY) crossed with pure wrinkled green (rryy) gives an F1 all RrYy, round and yellow. An RrYy plant makes four gametes, RY, Ry, rY and ry. The F2 has round yellow, round green, wrinkled yellow and wrinkled green in the ratio 9 : 3 : 3 : 1, so the two traits are inherited independently.
The worked solution
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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. If they travelled together. Round would always go with yellow, and wrinkled with green. Only the two parent kinds could appear.
Step 2. What happens. The F1 plant puts R or r into a gamete separately from Y or y. So Ry and rY gametes form too.
Step 3. The result. These gametes give round green and wrinkled yellow seeds.
Answer: the new kinds can only form if the two genes are passed on separately, so the traits are inherited independently.
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