Thanks KarenO: your POV is appreciated.
What I'm wondering is how much segregation you continue to see in F4, 5, 6... after you have selected the plant you love from F2 and F3 generation. How many plants did you need to grow to find one identical to your chosen prior generation? Or expressed as a ratio, how many of four or six or ten plants are so similar by F4, 5, 6... that you can't really tell them apart?
As Carolyn pointed out, that would depend to some extent on the cross, how wide ie how much variation is there that has to be rendered homozygous. Obviously if the parents are very similar then there will be more stability early on. Also if the parents are not themselves stable, there's going to be more variation, potentially, for generations to come.
And chance plays a part as well, in the segregation. So for example, I have two sibling lines from a cross between an F3 and an F1 - one of them had a high degree of similarity to the selected F1 (skipper) - meaning that 4/6 F2 plants had the same fruit shape and size, and similar quality. One had the recessive pink-black trait but otherwise entirely similar. But the other sibling F2 was all over the map, none of them matching the shape and size of the original selection (rodney). So it stands to reason, I need to grow more of that F2 to find the one I was looking for, and I expect it to take longer to stabilize because that line contains a lot of divergent traits.
|