Final answer:
A point mutation affects a single base pair, potentially leading to silent, missense, or nonsense mutations, and involves either transition or transversion substitutions.
Step-by-step explanation:
A point mutation affects only a single base pair in the DNA sequence. Point mutations can lead to various outcomes: they may be silent mutations if the mRNA codon still encodes the same amino acid, missense mutations if it causes the mRNA codon to encode a different amino acid, or nonsense mutations if it turns the mRNA codon into a stop codon, prematurely ending protein synthesis. Furthermore, there are two types of nucleotide substitutions involved in point mutations: transitions, where a purine is replaced by another purine or a pyrimidine by another pyrimidine, and transversions, where a purine is replaced by a pyrimidine, or vice-versa.