Step 1: Understanding point mutation.
A point mutation involves a change in a single nucleotide base in the DNA sequence of a gene. Step 2: Evaluating the options. (A) sudden change in the chemical make up of a gene: Correct. Point mutation alters the nucleotide sequence of a gene. (B) alteration in allele frequency: Incorrect. It relates to population genetics. (C) changes in gene arrangement in chromosome: Incorrect. This refers to chromosomal mutation. (D) gradual, continuous change in genetic make up: Incorrect. This describes evolution. Step 3: Conclusion.
The correct answer is (A) sudden change in the chemical make up of a gene.