Question

Chromosomal DNA sequences are maintained and replicated with such high fidelity that the sequence of the human genome is changed by only about three nucleotides each time a cell divides. You mention this astonishing fact to your mother, who has just read an article in the newspaper about human genetics. She exclaims that this seems to be a very mutation rate because changing the function of three proteins every time a cell divides should quickly lead to a defective individual. Give at least three reasons to explain the mistake in your mother's reasoning.

Answer 1

Mother's reasoning is wrong in this case of mutation rates in the human genome because of the following reasons:

Even the mutation is of three nucleotides per replication but there are several cross-checking mechanisms in our cell which check the mutated part of the DNA and replace it with the correct one.

Even if the mutation exists after the cross-check process it has a high chance that it will be in the junk DNA region as most of our DNA is made up of the junk DNA.

If also mutation occurs in a particular coding region of the DNA still the cell can function properly as there are many copies of that gene in a particular genome so the mutated copy will be eventually silenced by the DNA modifications and the cell is free to behave normally.

Also if some drastic mutation takes place during the replication which has a severe effect on the organism then certain cellular mechanism will be eventually activated which will kill the cell and hence, prohbotting the mutation to spread.