HardBiologyHigh School (9–10)GeneralHeredity and Evolution › Heredity and InheritanceNumericalBoard Exam
An F2 of the dihybrid cross gives 1440 seeds…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An F2 of the dihybrid cross gives seeds. Without sorting by colour, how many are round and how many wrinkled? What is the ratio of round to wrinkled, and what does it show?
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
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. Round. seeds.
Step 2. Wrinkled. seeds.
Step 3. The ratio. .
Answer: round and wrinkled, , so each trait on its own still follows the monohybrid ratio.
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