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Scientists first thought that proteins, which are found in chromosomes along with DNA, would turn out to be the sought-after genetic material. Proteins were known to have diverse amino acid sequences, while DNA was thought to be a boring, repetitive polymer, due in part to an incorrect (but popular) model of its structure and composition.

Was Mendel (1822-1884) one of these scientists?

Note that in 1869, Friedrich Miescher isolated "nuclein," DNA with associated proteins, from cell nuclei. He was the first to identify DNA as a distinct molecule.

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    $\begingroup$ Did Mendel really even know about proteins? AFAIK they aren't really relevant to his work - just as Darwin didn't need to know the mechanisms of heredity to know, from observation, that it exists. $\endgroup$ – jamesqf Jan 17 at 18:36
  • $\begingroup$ @jamesqf You ignored the note that I added to this question. He probably heard about proteins and nucleic acids in his lifetime. $\endgroup$ – Me Now Jan 17 at 19:50
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    $\begingroup$ I would say "possibly" rather than probably, given his apparently rather isolated life. But the point I was trying to make is that (at least AFAIK) nothing in Mendel's work requires theorizing about the actual underlying mechanism of heredity. $\endgroup$ – jamesqf Jan 18 at 2:03
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    $\begingroup$ Your sense of scientific history is a little disoriented. Few geneticists were interested in the chemistry of the phenomenon until after the second world war. Genetics textbooks in the 1960s hardly concerned themselves with this. Mendel was a monastic plant breeder with acute observation and deductive powers. He was not a scientist in the modern sense, and cerainly had no interest in (and probably knowledge of) chemistry. $\endgroup$ – David Jan 18 at 23:12
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The first person to directly indicate a linkage between the hereditary material and enzymes was Garrod in 1902, based on the observation of the hereditary enzymatic disorder alkaptonuria. This is after Mendel's death.

The tetranucleotide hypothesis (i.e. DNA is not informative) that you refer to seems to have been formulated around 1910. So there is no way that Mendel knew about that.

It was not even proposed that proteins were composed of amino acids before 1902. No protein was sequenced before 1950. So Mendel had no idea what sequences or amino acids were, for any biopolymer.

It is formally possible that Mendel knew at some point about Miescher's result, but I'm not aware that he was at all interested in the chemical nature of Mendelian factors (what we now call "genes"). I agree with commenter @jamesqf on this point.

It was not immediately obvious to anyone that there was a discrete mapping between phenotypes and specific agents such as proteins. The major theories of inheritance at the time came from biometricians such as Galton, who believed that inheritance was driven by a blending-like mechanism (more or less), based on phenomena such as regression to the mean. They weren't really interested in the chemical basis either.

Mendelian genetics was only rediscovered around 1900 (Mendel was basically ignored during his lifetime), after which the debate started to consider the question of discrete genetic factors.

In short, I don't think that there is any evidence that Mendel had any interest in chemistry or the chemical relations of the organismal characters he studied.

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