Explanation of hybrid vigor


Link: www.sciencedaily.com/releases/2002/06/020612072701.htm

Henry this is a very interesting article. I just wish they did this experiment with something other than corn. From my undertanding corn is unusal in that even in open pollinated varieties it needs a much wider base of genetic material than most plants. If it is inbreed to long it does not take long for a severe genetic depression to occur preventing them from even functioning. Maybe this experiment does not give a reason for say why hybrid vigor happens but it gives a reason why corn needs a much wider base. I would love to see them do this same experiment using a plant species more in the middle of the extreme. One extreme being corn another extreme being lupins which can go through decades of inbreeding without any sign of lost of vigor. Roses would be a good median plant. But this is something to think about. By the way thanks for the new site I did not know about this science daily seems like something I would want to read more of.

Henry, You have found one of my all time favorite papers. I love papers that shake up how we think about things - in this case that all alleles in an individual have allelic counterparts in a second individual. I feel that the most important aspect of this paper, however, has less to do with the genes and more to do with the repetitive DNA or what has been called “junk” DNA. There is absolutely no alignment (corespondence) between the 2 lines in the repetitive DNA sequences. This has potentially huge implications with regards to crossing over and even more importantly with regards to causes of genetic variation. The repeptitive DNA is starting to be recognized as a major “cause or influence” of genetic differences.

Adam, this phenomenon has also been observed in other species - humans for example. Redon et al. 2006. Global variation in copy number in the human genome. Nature 444. I think that once enough species have multiple genomes sequenced that this will turn out to be the norm rather than the exception.


The science daily article is an interesting piece of hype for the work of a very good scientist- Hugo Dooner. I’ll have to read the original to see what they actually did. But I believe that I wrote an article for the RHA newsletter recently that addresses the flip side of this, something called linkage disequilibrium. I think it is coming in the next issue.

Hybrid vigor is a lot more than just additional members of gene families, or else tetraploids would be twice as good as diploids. It is all about getting the right balance of various factors in metabolism. A homely analogy is the synergy of the Colorado Rockies or Boston Red Sox. If you took half the players of each team and made them into two new teams they wouldn’t be nearly as good. That’s why our pro B-'ball teams alway do poorly in olympics.

Actually maize inbreds are pretty good yielding as they are. The hybrid vigor effect these days is not huge. A hundred years ago inbreds had lots of defects and the crossing helped overcome those. With strong selection, we can have pure lines with quite good yields.

In wheat, sorghum and rice, hybrids have never paid off with enough of an increase in yield to be worth the effort. And that’s not for want of trying by several big companies over many years. So maize is a little bit of an exception, probably because you can cut off the tassles cheaply and don’t have to use male steriles to produce hybrids.

Remember that maize is an outcrossing crop so it is designed to tolerate being mixed up. Lupines on the other hand are basically self-pollinating, like peas, soybeans and most legumes. So inbreeding does little harm.

As for roses, I’d dare to say we wouldn’t recognize hybrid vigor ( of the kind seen in maize) if we saw it. We don’t have two inbred lines of even 3 generations except possibly in tetraploid species because diploids are generally reported to be pretty much self-sterile, and the tetraploids may go self-sterile if deliberately inbred 3x. I’d be really interested to hear of a verified example of 3 or more gens of selfing in a species. With a non-species we would need 6-8 gens to get a real inbred. Then we’d have to have a way to measure that the offspring in a cross outdid both parents by some quantitative measure. In nature, species hybridize and intergrade right across North America and there doesn’t seem to be extra vigor in the interspecies hybrids. So if there is heterosis it won’t be a very big effect I’d guess.

lol, I wish there was a way to make 20" rose blooms on giant rose trees about 50’ tall.