Which of the following situations does not describes a chromosomal mutation?

Which of the following situations does not describes a chromosomal mutation?

a. A cytosine nucleotide is substituted for thymine nucleotide in a gene.

b. The sister chromatids of Chromosome 18 do not separate during anaphase II.

c. A portion of Chromosome 4 is deleted during interphase of meiosis.

d. A section of Chromosome 17 is duplicated leading to problems in the peripheral nervous system.