What name is given to a sudden change in a gene or chromosome?

Step 1: Analyze the question The question asks for the term describing a sudden change in a gene or chromosome. The key words are "sudden change."

Step 2: Explain the concept Let's check each option:

• A. Allele: One of the alternative forms of a gene at the same locus (e.g., T for tallness and t for shortness). It is a version of a gene, not a change.
• B. Genotype: The genetic makeup of an organism, such as TT, Tt or tt. It describes the genes present, not a change.
• C. Mutation: A sudden, random change in the structure or number of genes or chromosomes. It can happen naturally or be caused by mutagens such as X-rays, UV light, gamma rays and certain chemicals. This matches the question.
• D. Phenotype: The observable physical features of an organism, such as height or skin colour. It results from genotype and environment, and is not a change in genes.

Step 3: Solution Only mutation means a sudden change in genetic material. Types include:

• Gene (point) mutation: a change in a single gene, for example sickle cell anaemia.
• Chromosomal mutation: a change in chromosome structure or number, for example Down's syndrome (an extra chromosome 21).

Step 4: Answer The correct option is C. Mutation.

Tip: Think "MUTation = MUTant", something that has suddenly changed. Also remember: Allele = alternative form, Genotype = genes, Phenotype = physical appearance.