MediumBiologyHigh School (9–10)GeneralHeredity and Evolution › Heredity and InheritanceConceptualBoard Exam
Two pea plants are crossed. About half of their offspring are tall and half are short…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two pea plants are crossed. About half of their offspring are tall and half are short. One parent is short. What are the genotypes of both parents? Explain how you know.
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. The short parent. Short is recessive, so this parent is tt.
Step 2. The other parent. Half the young are tall, so it gives T to some young; it must be tall. Half are short, so it also gives t.
Step 3. Check. Tt crossed with tt gives Tt and tt in equal numbers: half tall, half short.
Answer: the parents are Tt (tall) and tt (short).
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