Francis Crick developed the model of protein synthesis which he called the central dogma (1958) which states that DNA makes RNA makes protein. The dogma emphasises the unidirectional pathway from DNA (the archives of genetic material) by transcription converted to mRNA and then converted into specific amino acid sequences of proteins by translation.

Another step can be added: Amino acid sequences determine protein structure. Most proteins adopt specific 3D conformations dictated by their amino acid sequences alone. Protein structure determines protein function.

This one-way flow requires Darwinian natural selection at the protein level to be a mechanism of evolution – as opposed to direct selection of DNA sequence changes. This is achieved through mutation which generates variation (which changes individual DNA sequences) but does not move a population to a better-adopted state.

The ribosome makes possible the connection between heritable genetic information (as a nucleic acid) and the agents of biochemical activity (proteins). Selection acts as the functions produced by the proteins, and RNAs encoded in the genome and on the regulatory mechanisms.

Some genetic change is non-selective: neutral evolution or genetic drift. Drift is especially important in small populations. The result of both selection and drift are inherited alternations in genomes – including both changes in sequence and changes in allele frequencies. The changes change the nature and expression patterns of the proteins and RNAs in individuals of a population.

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