I only grow vegetables, but the same type of principles apply to any plants or animals. Mendelian Inheritance is a good theory for working with highly inbred homozygous lines in a classroom. From time to time I am able to observe simple segregation in the garden. In the field when dealing with multiple interacting traits in highly heterozygous populations, i haven't found Mendelian genetics to be of much value. For the most part in the plants I work with, there are multiple genes that interact with each other, and with the environment, to determine what the plants looks like, and how they grow. The resulting traits in the offspring can be so complex and muddled up that it's difficult to observe and draw any conclusions about the responsible genes. For example, if only 6 genes are interacting to produce a certain trait, they can produce more than 4000 different combinations: Not the 1 in 4 chance that they talk about in the classroom for a single gene interaction. To get around this difficulty I often approach my projects by stating what the end goal is. Then I throw a bunch of seed in the ground, and let it survive or die, for a couple generations. I step out of the way and let the plants figure out how they are going to reproduce, and conform to my end goals. My radish seed crop for example must be resistant to grasshoppers, because plants that aren't resistant to grasshoppers don't produce seeds in my garden. I didn't start out by saying, "I need to select for a strain that is grasshopper-proof". The plants took care of that all by themselves.
I am currently working on developing a short-season cushaw/mixta squash. I figure that if I throw enough different kinds of mixta seed into the ground for enough years, that eventually something will survive long enough to produce offspring. Right now the only criteria for my mixta breeding project is: "Must produce seed". If that ever happens in my garden, then I can work on something like: "Must taste good".
This year I discovered an okra plant that tolerated one more day of frost than any other okra in the garden.
