Mutations

Comparing the original and new sequence, an extra base 'A' has been added into the sequence. This is an insertion mutation — one or more extra bases are added.

The genetic code is read in groups of three (codons). Adding one base shifts the reading frame for every codon after the insertion point. This is called a frameshift mutation.

Because all codons downstream of the insertion are changed, a completely different set of amino acids is produced from that point onwards. The resulting protein is almost certainly non-functional.

The correct description is an insertion mutation causing a frameshift that alters all codons after the insertion point.

We need to identify the type of mutation and its effect on the genetic code.

A substitution swaps one base for another — no extra base is added. The question clearly states a base is inserted, so the option 'Substitution mutation causing a single amino acid change' is incorrect.

A deletion removes a base. Here a base is added, not removed. Also, frameshifts alter codons after the mutation point, not before. This option is doubly incorrect.

Degeneracy (multiple codons coding for the same amino acid) can make a substitution silent, but it cannot rescue a frameshift — the entire reading frame is disrupted, affecting many codons simultaneously.

The remaining option — insertion mutation causing a frameshift with all downstream codons altered — correctly describes what happens when an extra base is added to a DNA sequence.

Only germline mutations (in sex cells — eggs and sperm) can be passed to offspring. Somatic mutations affect the individual's body cells only.

Lung cancer develops in lung cells, which are somatic cells. These cells do not contribute genetic material to the next generation.

Because the lung cancer mutations are in somatic cells and not gametes, they cannot be inherited by children.

We need to explain why a parent's cancer mutation is not passed to offspring — the key concept is which types of mutations are heritable.

This is factually incorrect — many cancer-causing mutations are dominant (e.g. in oncogenes). Recessiveness has nothing to do with why lung cancer isn't inherited.

The immune system can destroy abnormal cells, but the reason the mutation is not inherited has nothing to do with the children's immune system — the mutation was never transmitted in the first place.

Tobacco smoke chemicals cause gene mutations (e.g. base changes), not exclusively chromosomal mutations. This statement is factually wrong.

The correct explanation is that lung cancer mutations occur in somatic cells (lung cells), which do not contribute to gametes. Without being in a gamete, the mutation cannot be inherited.