MCB 150 Frequently Asked Questions

Mutations

I know that 1 or 2 bases added or deleted is considered a frameshift mutation and 3 bases added/deleted is in its own sort of category for mutation type. What sort of mutation is it considered when 4,5,6,7, etc. bases are added/deleted? Does this ever happen? Because I know an insertion or deletion involved 100's or large amounts of base pairs. I'm just wondering where the line is drawn between a point mutation and chromosomal mutation and what happens if there's a "gray" area in between.

Any small number of bases added or removed that isn't divisible by three is truly a frameshift. Small numbers that are divisible by three are still thrown into the frameshift category because, as you pointed out, we don't have anywhere better to put them. As far as a magical dividing line between frameshifts and chromosomal-level mutations, there isn't one. So don't worry about me giving you a question on your exam that asks about the insertion of 70 bases. This would probably be big enough to be a true insertion, but if I write a question like that, it'll be 2 or 2,000, if you see what I mean.

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