A plant breeder wants to know whether a tall pea plant is TT or Tt…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A plant breeder wants to know whether a tall pea plant is TT or Tt. She crosses it with a dwarf plant and gets offspring, and all of them are tall. She says that the plant is TT.
A Tt plant gives a tall offspring with a chance of in a test cross, and each offspring is independent.
- If the plant were really Tt, what is the chance of tall offspring in a row, as a percentage?
- She wants the chance of this mistake to be below . What is the smallest number of offspring, all tall, that she needs?
Need a reminder? The key ideaShow
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. A Tt parent gives a tall offspring in a test cross with the chance .
Plan. The offspring are independent, so multiply the chances.
Step 1. (a) For offspring, all tall: . As a percentage, this is .
Step 2. (b) We need , that is, . Now is too small and is enough. So . Check: .
Answer: ; at least offspring.
Check. With offspring the chance of the mistake is , which is above .
Watch out. A test cross can never prove that a plant is TT. It can only make the mistake very unlikely.
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