We've known that offspring inherit various traits from their parents since (at least) Aristotle. In The Elements of Plant Hybridization, Gregor Mendel treats that fact as common knowledge. Clearly, we don't credit Mendel with discovering it. Accordingly, it seems to me that Mendel's only notable discovery was the discovery of the existence of dominant and recessive genes. However, that discovery doesn't seem to justify the title 'founder of modern genetics', which Wikipedia, and other sources, use to refer to him.

Why is Mendel the big deal that he is?

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    $\begingroup$ I think he did more than discover dominant/recessive, he discovered ratios of traits in offspring, like the 3/4 dominant 1/4 recessive phenotype, and that organisms could carry a gene for a trait without showing it, then pass that trait to it's offspring. The whole thing suggested that there were rules governing inheritance which could be deciphered and used to breed plants/animals more effectively. Darwin suggested that traits were selected for by environmental pressures, but Mendel showed how traits were passed down. $\endgroup$ – user137 Jul 16 '15 at 1:49
  • $\begingroup$ Aristotelian pre-science wasn't concerned with experimentation at all - it was just people throwing hypotheses around, basically. Contrast with Mendel, who developed a strong theoretical framework, coupled with precise experiments, tons of data and actually increased understanding of the subject matter. In other words, his was the first book on the subject that actually presented not just ideas, but also hard data anyone could verify for themselves. Not to mention that he also did deliberate genetical engineering on a level never done before. $\endgroup$ – Luaan Jul 16 '15 at 7:34
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    $\begingroup$ mac122.icu.ac.jp/gen-ed/mendel-gifs/18-mendel-cartoon.JPG $\endgroup$ – Bob Tway Jul 16 '15 at 8:05
  • $\begingroup$ @Luaan there's also the suggestion that he may have "doctored" some of his data... $\endgroup$ – MattDMo Jul 18 '15 at 4:39
  1. Independent assortment. Mendel showed that his genetic markers for different traits, or phenotypes are transmitted randomly to the F1 generation. This was before the concept of linkage was discovered, so fortunately he selected unlinked genes.

  2. Segregation of alleles. The dominant and recessive alleles segregate away from each other when the germ cells are created, therefore each parent has two copies of every Gene.

  3. Distinguishing phenotype from genotype in a predictable and testable framework.

  4. The test cross. It was only careful record keeping and back crosses that revealed the recessive copies of mutant alleles in heterozygotes.

One description of his contributions is available on Wikipedia. Other sites include MendelWeb, Learn Genetics,

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    $\begingroup$ great answer +1. A reference would be nice to allow people to look up background info to your answer. $\endgroup$ – AliceD Jul 16 '15 at 2:16

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