Question

Which of the following frameshift mutations might be expected to have the least impact on an organism?
a deletion of two nucleotides near the beginning of a gene
an insertion of three nucleotides in the middle of a gene
a deletion of four nucleotides near the end of a gene
an insertion of five nucleotides at a gene’s promoter site

Answer 1

Okay....I THINK I know the answer to this one!

There are THREE nucleotides in one codon. You know that, right?

The letters, in DNA, always come in groups of THREE.

Like....AAT...AAC....GGC...

You get it?

Now...look at the second choice.
"An insertion of three nucleotides in the middle of a gene."

If you insert three nucleotides into a gene,
it's the same thing as inserting ONE codon.
(3 nucleotides = 1 codon)

And since codons NORMALLY have 3 nucleotides anyway,
then I don't think that inserting three more codons into the gene is going to affect it very much.
As long as it's THREE!

If you were to insert ONE, or TWO extra nucleotides into a gene,
it would totally mess up the order of the codons.
Because codons come in groups of 3.