Quick questions on Types of mutation: point, silent, frameshift and chromosomal: HSC Biology Module 6

A point mutation changes a single base pair in the DNA. There are three structural sub-types.

Substitutions are further classified by what they do to the protein.

A frameshift is caused by an insertion or deletion of a number of bases not divisible by three. Every codon downstream of the mutation is shifted, so the amino acid sequence past that point is essentially random and a premature stop codon usually appears within a few codons. The resulting protein is truncated and non-functional.

A chromosomal mutation changes the structure or number of whole chromosomes. These affect many genes at once.

One base is replaced by another (e.g. A to G). The reading frame is unchanged; at most one codon is altered.

An extra base is inserted into the sequence.

A base is removed from the sequence.

Sickle cell anaemia is a single substitution (A to T) in the beta-globin gene, changing codon 6 from GAG to GTG. This is a missense mutation: glutamic acid becomes valine. The altered haemoglobin polymerises under low oxygen, deforming red blood cells.

"Classify/identify" wants the correct label; "explain the cause" wants a mechanism (e.g. non-disjunction); "compare" wants the same features (cause, process, effect) for both types.