Mukherjee spends a significant number of pages early in the book covering Mendel's life and work. The narrative is much the same I was taught in high school and college, and participated in teaching as a graduate teaching assistant. Mendel lived in the Austro-Hungarian empire, a fascinating and complex domain skipped over in all my public school courses, other than the fact that the assassination of the heir-to-the-throne triggered World War I. To obtain an education, he became a monk in a town then called Brünn (German) but now Brno (Czech). After a number of misadventures with various exams and such (such as trying to breed mice, which his abbot puts a stop to), Mendel turns to his affinity for gardening. Over many years, he interbreeds peas, starting with pure-breeding lines for seven traits. Meticulously measuring and recording his data (some 40,000+ peas!), he observes specific ratios in his crosses and deduces that some traits can disappear in one generation and reappear in another. He names these states "dominant" and "recessive" and posits that genetic information is carried in atomic units of some sort.
Mendel presents his work to the local scientific society and publishes it in their obscure journal, where it is virtually ignored. He sends reprints to a number of libraries and scientists around the world, which has little impact. His work is cited "four times", according to Mukherjee.
Mendel does succeed in engaging one prominent botanist in correspondence, Karl von Nägel. Unfortunately, this turns out to be a two-fold disaster; von Nägel increasingly insults Mendel as a country bumpkin and even worse suggests that Mendel repeat his efforts with a plant called spotted hawkweed. Unknown at the time, spotted hawkweed reproduces by apomixis, that is requiring no pollination. So all Mendel's motions of trying to specifically cross-pollinate flowers are wasted motion, and the data useless. Mendel is promoted to abbot, which consumes all his time. His death is barely noticed outside the abbey and his notebooks are burned. Eventually, three different scientists rediscover Mendel's work after generating similar results, and so Mendel is belatedly crowned the founder of an important new science.
Mukerhjee goes into much more detail with a lot of color; I'll try not to repeat my book report I wrote on the Hood biography (I don't know if Luke Timmerman will ever forgive me for spilling so many juicy bits).
My one bit of research into this topic was last New Year's Eve. On leave from Starbase, TNG were wandering downtown Boston waiting for my wife to escape her career obligations (she works in a public library). After some truly random wanderings, TNG suggested we go to the Boston Public Library. It hit me that I could finally access a book which is on reserve there, a glorious coffee table-sized book on matte painting. The particular room that book is held in is open only on weekdays, and I had all but expected another layoff to be the only way I'd get to see it. Once I had reveled in that book (it really is a great exploration of the history and technology of this special effects craft), we still had plenty of time.
After that, TNG asked if I might want to check out the Rare Books Room, which sounded like an adventure. But what to look for? Then it hit me: Matt Meselson, while teaching genetics at Harvard, had claimed that Mendel had sent a copy of his manuscript to the Boston Public Library. Why not go find it? So I went through the procedure to register for access and then the quick training (mostly what you aren't allowed to do), then entered the room. It's really a gorgeous reading room, richly paneled with wood. Alas, the catalog had no entry for Mendel; Matt Meselson was apparently mistaken. Too bad, because when he had said that I had asked him afterwards if he had ever looked to see who had checked it out, which had apparently never occurred to him. Anyway, I "settled" for scanning a first edition of The Origin of Species, which isn't a bad consolation prize!
As I said, that is the conventional narrative. There are variations on the theme. For example, Mendel's numbers are "too good", with too little deviation from the pure ratios. Mukherjee mentions this briefly. Perhaps Mendel threw out some datapoints or stopped counting when his ratios looked good. Meselson made some comment that there could be a way to explain it by biology; if I remember correctly the peas in a pod may not be fully independent of each other. But for the most part, there is a common narrative which is found in most references and textbooks.
Somewhere recently I stumbled on a revisionist view of Mendel. I don't necessarily buy this interpretation, but it does make some interesting claims. I've used a freely available piece for my main source here, but others corroborate it.
The first revisionist claim is that Mendel was studying only hybridization, not heredity. This is akin to Priestley not truly discovering oxygen, as he applied the wrong (phlogiston) theory to his findings. Similarly, the revisionists argue, nowhere in Mendel's published work is a word for "heredity" or "inheritance". The next big claim is that Mendel never mentioned the 9:3:3:1 ratio for a dihybrid cross, and yet another is "Mendel's Laws of Heredity" are entirely a post-facto creation which Mendel never envisioned. Furthermore, Mendel never wrote "of particulate determiners, either paired or unpaired". His math is too simple! Plus his peas might have represented multiple species. Furthermore, the revisionists argue that Mendel was cited far more than usually claimed, but in other works on hybridization.
So why, in the revisionist view, was Mendel credited far beyond his due? Why the legend? It's simple: Mendel was a convenient solution to what was turning into an ugly dispute on priority. Three different scientists, Holland's Hugo de Vries, Carl Correns of Germany and the Austrian Erich von Tschermak, had all found results similar to Mendel and then found Mendel. In the case of de Vries, he apparently even published one paper adopting Mendel's dominant-recessive terminology without citing Mendel. Rather than argue over who was first, it was more civil to simply endow Mendel as the pioneer and re-frame his work. Mendel was long dead, so couldn't protest. Besides, there was no time to waste: if three independent groups could make the rediscovery, than perhaps a fourth was imminent (and indeed, the American William Jasper Spillman was hot on the trail as well).
Other than mentioning Corren's sniping at de Vries, Mukherjee doesn't report much on this soap opera. What to include and omit will probably be a central theme of my review, so I won't explore that much here. Still, that the area isn't fully settled could have been a useful addition to the book.
Of course, every revision provokes a response. For example, "What Did Mendel Think He Discovered" rebuts most of the revisionist points, conceding that the Mendel legend has been exaggerated a bit but is mostly deserved. But they don't yield on the idea that Mendel was thinking about heredity in addition to hybridization.
Care to explore the topic on your own? MendelWeb has many resources. My German isn't nearly good enough to read the original, let alone parse the arguments the revisionists and counter-revisionists make over Mendel's choices of terms. While not as many translations exist as, for example, the Christian Bible, apparently there are multiple English translations of Mendel's book out there. One of the first was made first by a translator and then edited by William Bateson. That seems to be the only translation available freely online. MendelWeb has a large number of notes for guiding an inquiry.
No matter which version of Mendel you accept (well, except insane Marxist-Lysenkoist ones), he remains an important experimenter and figure in the history of genetics. His history is full of enough blanks and questions to enable much argument, even before we layer on the complexities of translation and the passage of time. In the modern world, the ideas of hybridization and heredity have become so intertwined it is nearly impossible to think of them as distinct disciplines. I'm happy to view the revisionism as error bars on the canonical story, an inspiring story of a solitary monk toiling away in obscurity on a scientific mission in his garden.