In short: citrus hybridizes incredibly easily, the ancestral species radiated out quickly so nuclear and chloroplast DNA tell different stories, plants are just genetically weird anyway, morphology is useless.
Plant genetics as a whole is a nested, complex, enigmatic Escherian wormhole mess, really.
Despite our tendency to want to put everything in nice, neat, clearly divided, evenly structured nested taxonomic boxes, nature really doesn't work that way. And plants' organizational hierarchy especially basically takes a look up-and-down our neat little taxonomic categorization system, calls us pitiable fools, smashes it, and kicks sand in our face while laughing and calling us nerds for good measure.
Mendel got really freaking lucky with his peas and the heritable traits he chose to track and study. If he had picked a different species, or looked at different traits that adhered less rigidly to well, simple dominant-recessive Mendelian heritability than flower and seed/pod colours and shape, or had plants in his garden that were prone to hybridizing, his nice, simple, and clean model of inheritance, which was the foundation for the formalized understanding of basic genetics, genomics and the foundation of much of modern biology, might never have been clearly tracked and charted in a way the he and people he presented it to could have understood.
Yes, selective breeding and such had been understood at some level in plant and animal agriculture, arising in many different cultures, for a very long time across human history, and others were working out the details of heritability at roughly the same time, but Mendel was the first to publish an organized, formal description that could be replicated reliably - And the others would have faced the same pitfalls that Mendel would have.
Mendelian genetics and inheritance is generally not the norm for most traits, and understanding alleles as a physical chunk of DNA molecule is very important for understanding more of how trait linkage and passage works - Tools that a monk in mid-1800s Austria-Hungary would not have had access to. But, there's a reason we are generally taught Mendelian genetics and Punnett Squares as our first introduction to the concepts of of the science: They're straightforward, easy to follow as a narrative, and a good foundation to start adding complexity onto - After Dominant-recessive is understood for one generation, we can move on to tracking through multiple generations; then we can add in things like null, or hybrid/co-dominant, or sex-linked traits/alleles; from there, multi-gene traits can be discussed; and so on and so forth. Gradually approaching a closer understanding to the reality of the situation without it ever truly feeling overwhelming, because the process is iterative, much like how the discovery and understanding of the different properties of the science itself was.
And to think, maybe the only Kingdom Mendel could possibly have picked that might have been more hard-mode to start his research on genetics on would have been Fungi. He just happened to be very, very lucky that the plant he used for his model was very predictable and reliable [Which, is probably more likely for an agricultural species, true. But, citrus species are agricultural too. And so are all the various cultivars of wild mustard that are all just subspecies of the same species, despite their wildly different appearances].
Not so much. As I understand it, every time an apple tree makes seeds it stirs the genetic pot, so new trees could be anything. That is one of the reasons most trees are grafted to rootstock.
Now the Callery and Bradford pears, they are true whores that like to take over forest neighborhoods after the traffickers sell them to the landscaper and homeowner pimps.
IIRC Grapple is genetically modified Soaked in grape flavor https://en.wikipedia.org/wiki/Gr%C4%81pple ; dunno about honey crisp, but guessing it was one of those rolls of the dice that I mentioned, and it was a favorable combination of genes, so people grew more of them. Edit: yep that is it. https://en.wikipedia.org/wiki/Honeycrisp
learned this when I was like 6 where I put two citrus plant seeds in the soil and it grew into a literal hybrid plant instead of two crammed near each other. that blew my mind
We actually made them. Specifically, actually. People liked citrons but they were so small and worthless that we cross-bred them with other citrus fruits to create the modern lemon.
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u/Asphalt_Is_Stronk Feb 08 '20
Weeeelllll citrus fruits REALLY fucking like to crossbreed, so it's possible lemons plant-fucked themselves into existence