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Old January 4, 2017   #35
Keen101
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Quote:
Originally Posted by FredB View Post
Oddly enough, crossing green-fruited habrochaites with pink-fruited Brandywine resulted in orange fruit, an interesting example of what geneticists called epistasis (when you get a particular trait with a combination of two genes but not with either one separately). Apparently habrochaites is missing one of the genes on the pathway to orange pigment, and Brandywine is missing a different gene, but when you cross them the F1 has all the necessary genes and can make orange pigment
Nice. A cool cross to be sure. In peas this is really apparent when you cross a pink flowered vine with a white flowered vine. The result is a plant that has bicolor-purple flowers that neither parent have. In the pea example the gene A is the (dominant) gene that controls Anthocyanin (or color) expression. The pink flowered vine has at least one if not two copies of this "master switch" that allows it to have colored flowers, but must lack another dominant gene elsewhere as the flowers are pink instead of the wild bi-color purple. The white flowered plant has the bi-color gene hidden but since it has two recessive copies of the little "a" gene it has it's "master switch" turned off. So the expression of specific color is epistatic to the A "master switch" gene. Some call this a throwback phenomenon as you can suddenly see traits that have been hidden for generations suddenly show up seemingly out of nowhere.

Interestingly enough Darwin saw this happen when he bred pidgeons. He just didn't fully know what was going on. In his case he bred a white pidgeon with another white pidgeon (that had black tail feathers) and in his F1 generation he got a BLUE pidgeon. One had the master switch color gene but lacked another, the other had the blue gene but lacked the master switch.
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