Mendel has been the subject of controversy regarding whether his results were fraudulent. Hardly a great choice for an exemplar, whatever the truth is.
Linus Pauling (described as an "amateur biologist" in a caption) was hardly an amateur interested in the structure of DNA, having written his PhD on x-ray diffraction. In addition, he is introduced in the text as "Linus Pauli," a Nobel-prize winning physicist. This seems to be a Mendelian cross between Linus Pauling, the Nobel-prize winning chemist, and Wolfgang Pauli, the Nobel-prize winning physicist.
Francis Crick, who made the title as an example of the power of amateurs, was pursuing a PhD in the field of x-ray crystallography, which sort of disqualifies him an "amateur" in my mind. Those "careful biology experiments" were studies of x-ray diffraction images of DNA, making Crick's physics background entirely relevant.