MediumBiologyHigh School (9–10)GeneralHeredity and Evolution › Heredity and InheritanceConceptualBoard Exam
Nikhil has a tall pea plant, but does not know if it 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.
Nikhil has a tall pea plant, but does not know if it is TT or Tt. He crosses it with a short plant (tt). What will the offspring look like in each case? How can the result tell him the genotype?
Need a reminder? The key ideaShow
Each trait is set by a pair of gene copies, one from each parent. The dominant copy (T, tall) hides the recessive one (t, short). Pure tall (TT) crossed with pure short (tt) gives an F1 all Tt and tall. Tt crossed with Tt gives 1 TT : 2 Tt : 1 tt, so 3 tall : 1 short.
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. If the plant is TT. Every gamete carries T, so every young one is Tt and tall.
Step 2. If the plant is Tt. Half its gametes carry t, so about half the young are tt and short.
Step 3. Reading the result. If any short plants appear, the tall parent must be Tt.
Answer: all tall means TT; about half tall and half short means Tt.
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