Chromosomal rearrangements are considered large-scale mutations. Point mutations are considered small-scale mutations, and are of two general types. The first is a single nucleotide-pair substitution. What occurs here

Please find the explanation of what single nucleotide-pair substitution is below

Explanation:

Point mutation is considered a small scale mutation as stated in this question because it involves only ONE nucleotide in a sequence i.e. only one nucleotide base is changed or altered in the sequence.

Single nucleotide-pair substitution is a type of point mutation in which one (single) nucleotide base is replaced by another nucleotide base. For example, in a DNA sequence that reads: TAA GTC GGG, a mutated sequence affected by single nucleotide-pair substitution will read as follows: TAA GTC TGG

Note that in the last codon (GGG), a single nucleotide G has been replaced by another nucleotide T. Therefore, single nucleotide-pair substitution is said to have occur.