What is meant by codon bias?

Codon bias refers to the preferential use of certain synonymous codons over others for a particular amino acid in the genetic code. This phenomenon occurs because different organisms can exhibit varying frequencies of codon usage due to factors such as evolutionary history, gene expression levels, and adaptation to specific environments.

The concept encapsulated in the correct answer focuses on how codon bias is measured by assessing the departure from equality among the frequencies of these synonymous codons. In other words, if an organism has a codon bias, some codons will be used more frequently than others to code for the same amino acid, deviating from an equal distribution. This can reflect underlying evolutionary pressures and functional adaptations that influence which codons tend to be more favorable in specific contexts, like translation efficiency or accuracy.

This understanding of codon bias is crucial for interpreting genetic data, especially when analyzing gene sequences and their expression patterns across different species or in response to various stimuli.