First thing to know: all viruses (but also bacteria, fungi …) have a genome, that is to say a “genetic identity card” which defines their properties – their morphology, for example. This genome is not fixed: when the virus multiplies, its “genetic program” can evolve – in the same way that the genome of the human species has gradually changed over generations.
“There are two types of modifications (or mutations) in the genome of an organism: genotypic changes only correspond to silent genetic mutations that have no impact on the properties of the organism (whether it is a virus, bacteria or other), explains Prof. Michel Cogné, professor of immunology. On the contrary, the genotypic and phenotypic changes have an impact on the properties of the organism – they are said to be expressed.“
“To illustrate this complex notion, we can take the example of an e-mail: if the spelling of a word in this e-mail is modified but the meaning of the message remains unchanged, we have a “simple” modification. of the genotype. On the other hand, if the spelling variation results in a different meaning, it is a change in the genotype associated with a change in the phenotype.“
When a virus multiplies, genotypic and phenotypic modifications (expressed, therefore) are likely to appear: we then speak of “variants”.
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