Chapter two of Dobzhansky’s Genetics and the Origin of Species is a summary of lessons learned surrounding the enigmatic ‘mutation’. What is so fascinating about this is that, first of all, he addresses a number of misconceptions that the public still have about mutations today, and, secondly, he did this without knowing the mechanisms behind mutations. For example, today we know that point mutations can occur in DNA. This is when one of the bases in a DNA molecule gets swapped for another one. Thus a C (the molecule cytosine) get could replaced with a T (thymine), which could potentially affect the appearance or behaviour of the organism. In 1937, everyone knew that biological information was stored in the chromosomes. It was known that chromosomes were somehow composed of genes (stuffed into the chromosomes like a sausage, according to Dobzhansky), and that sometimes parts of chromosomes could break off, switch around, go missing, get doubled. But no one knew that genes were made of DNA. No one knew that there were four 'letters' to DNA. No one knew that mutations could occur in the DNA. Yet Dobzhansky could still with full confidence talk about point mutations! He knew they had to exist, even if he could not explain how.
Today I would like to give a snapshot of the lessons Dobzhansky learned when studying mutations.