A student grows the F2 of a dihybrid cross, RrYy × 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 student grows the F2 of a dihybrid cross, RrYy × RrYy. R stands for round seeds and Y for yellow seeds. She collects seeds from the F2 plants.
- How many round yellow seeds does she expect?
- How many wrinkled green seeds does she expect?
- How many seeds are homozygous for both genes (RRYY, RRyy, rrYY or rryy)?
Need a reminder? The key ideaShow
Genes on different chromosomes assort independently, so you can multiply the chances of the separate genes. RrYy × RrYy gives 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green. A plant heterozygous for genes makes kinds of gamete, and its F2 has genotypes.
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.
Given. RrYy × RrYy, seeds.
Plan. Use the boxes of the Punnett square. One box stands for seeds.
Step 1. (a) Round yellow has boxes: seeds.
Step 2. (b) Wrinkled green has box: seeds.
Step 3. (c) Each of RRYY, RRyy, rrYY and rryy sits in one box, so boxes: seeds.
Answer: seeds; seeds; seeds.
Check. .
Watch out. Round yellow is not the same as RRYY. Only one box in the nine round yellow boxes is RRYY.
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