HardBiologyHigh School (9–10)GeneralHeredity and Evolution › Heredity and InheritanceConceptualBoard Exam
A man with blood group A marries a woman with blood group O.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A man with blood group A marries a woman with blood group O. Their daughter has blood group O. Is this enough to tell which trait, A or O, is dominant? Explain.
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. Suppose A is dominant. The father could carry one A and one O copy. The daughter could get O from each parent, and be O.
Step 2. Suppose O is dominant. The daughter needs only one O copy, which her mother can give. She would be O.
Step 3. Both fit. Each idea explains the family, so the family alone cannot decide.
Answer: no; the result fits whether A or O is dominant, so more families are needed.
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