A sudden change in the genetic composition of an organism is termed

Step 1: Analyze the question The question asks for the term for a sudden change in the genetic composition (genes or chromosomes) of an organism.

Step 2: Explain the concepts

• Mutation: A sudden, random change in the DNA sequence of a gene or in the structure or number of chromosomes. It can be spontaneous or caused by mutagens such as X-rays, UV light, or certain chemicals. Mutations are heritable if they occur in gametes.
• Linkage: The tendency of genes located on the same chromosome to be inherited together.
• Variation: Differences among individuals of the same species. These may come from genetic causes (including mutation) or from the environment, and they are not necessarily sudden.
• Epistasis: An interaction in which one gene masks or suppresses the expression of another gene at a different locus.

Step 3: Match the definition

• "Sudden" together with "genetic composition" points directly to mutation.
• Linkage describes inheritance patterns, not a change.
• Variation is a broad result, not a sudden genetic event.
• Epistasis is about gene interaction, not change in the genes themselves.

Step 4: Answer The correct option is A. mutation.

Tip: Link the keyword "sudden" with "mutation." Also remember that mutation is the ultimate source of new genetic variation. Linkage means "linked together," and epistasis means "one gene masking another."