Final answer:
The vast majority of mutations are probably neutral, meaning they do not have a significant effect on the organism's fitness or result in changes to the phenotype.
Step-by-step explanation:
The vast majority of mutations are probably neutral. Most mistakes during DNA replication are corrected, and those that are not can lead to mutations, defined as permanent changes in the DNA sequence. These mutations come in various forms, such as substitution, deletion, insertion, and translocation. While some mutations like the CCR5-4³32 confer advantages such as HIV resistance, others can result in genetic diseases or even cancer. However, the majority of mutations do not directly affect the organism and thus, are considered neutral mutations. These include silent point mutations where the amino acids in proteins remain unchanged due to the redundancy in the genetic code.
Germline mutations are inheritable and can cause diseases or increase the likelihood of illness, as seen with the BRCA2 gene and breast cancer. Some mutations do not express themselves and are termed silent mutations. Mutations such as point mutations only affect a single base pair and can be a transition or transversion. In transitions, a purine is replaced with another purine or a pyrimidine with another pyrimidine, while in transversions purines are replaced with pyrimidines and vice versa. Insertions, deletions, and translocations can also occur. The long-term accumulation of mutations can lead to significant evolutionary changes over time, despite individual mutations often being neutral or harmful.