A DNA fingerprint of a child has six bands, at 10.2, 6.8, 5.6, 3.3, 2.6 and 1.2 kb…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A DNA fingerprint of a child has six bands, at , , , , and kb. The mother has bands at , , , , and kb. Two men, A and B, claim to be the father. Man A has bands at , , , , and kb. Man B has bands at , , , , and kb.
- How many bands of the child cannot have come from the mother?
- How many of these bands are found in man A?
- How many of these bands are found in man B?
- Which man can be the father?
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. The bands of the child, the mother, and the two men.
Plan. Find the bands that the child did not get from the mother. The father must have all of them.
Step 1. (a) The child shares , and kb with the mother. The other three, , and kb, must be from the father. So 3 bands.
Step 2. (b) Man A has , and kb. That is 3.
Step 3. (c) Man B has kb only. That is 1.
Step 4. (d) Man A has all the bands that the father must have. Man B lacks two of them. So man A can be the father, and man B cannot.
Answer: ; ; ; man A.
Check. Sharing one band does not make man B the father, because the father must have all three.
Watch out. A match shows only that a man can be the father. A fingerprint with more bands makes the match much stronger.
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