Very interesting Bruce.

If we assume that one fish population is 1.5 pounds, and the other fish population is 3 pounds then one might suspect that the hybrid offspring might be, lets say 2.25 pounds which would be the average of the two (after many many crosses).

With hybrid vigor / heterosis, you might see that the population of hybrids actually have a weight of 2.35 pounds, which is greater than the average of the two parentals.

Hybrid vigor / heterosis just means greater than the average expected. Not greater than the parentals. Intuitively, and scientifically (unless there is a mutation within a promoter that controls growth) we would not expect the offspring to be greater than both of the parentals. Just one of the parentals (the smaller one... but remember this would only be if size was the trait that is experiencing the hybrid vigor. It does not always happen this way. Just an illustrative example).

I really made a BIG mistake when I said that the hybrid would be larger than the Parentals. What I really meant was that I would expect the hybrid to be larger than ONE parent, with an average weight larger than the average of BOTH parentals.

I apologize for completely screwing that up. I think I am going to stop writing things after midnight. Never comes out how I thought I wrote it when the morning rolls around. Pretty embarrassing.

The problem with heterosis in most animals is that it is extremely difficult to find two populations that are far enough apart genetically. If they are very similar from a genetic standpoint, then the effectiveness of hybrid vigor is lowered significantly. I don't know enough about fish and their relatedness to say anything of value as far as that goes.




Last edited by Gflo; 06/28/10 01:41 PM. Reason: Terrible at typing
Dr. Flores D.V.M.