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As good an explanation of hybrids and polyploidy as I have seen in a long time.

http://waynesword.palomar.edu/hybrids1.htm#polyploid

What a superb find of yours Amaranth. Thats the most interesting and informative article that I have read in a long while.

Mike Kremer.

Amaranth, you're right. We were using colchicine to make polyploids when I did my agriculture degree in the mid 60s. Polyploids happen naturally also. They often don't survive in the wild because of infertility or at least reduced fertility. But I suspect tetraploidy occurred way back when grains were first domesticated. The tetraploids could survive because of cultivation.

By the way hybrids between a female donkey and male horse are sometimes fertile. Don't ask me how the chromosomes separate during meiosis. It's probable that any extra chromosomes in species within the genus are actually the product of a split chromosome. Therefore two chromosomes simply attach end to end along one.

Regarding hybrid oaks. We have some plants here called Alseuosmia. All sorts of regional leaf shapes throughout NZ but each leaf shapes breed true. Some are recognised as hybrids but it seems others may derive from ancient hybrids within the species. Some people believe the plants take on the leaf shape of the most common other species around them. We'll work it out one day.

Regarding fertility of hinnies and mules:

http://www.ncbi.nlm.nih.gov/sites/entrez...p;dopt=Abstract

Seems in China both have been shown to be fertile. Could be suspect of course. And regarding Mongolian and domestic horse hybrids:

http://www.iht.com/articles/2005/10/12/healthscience/snhorses.php

From the article:

"Teri Lear, an expert in horse genetics at the University of Kentucky, said comparisons of mitochondrial DNA, the genetic material inherited through the maternal line, showed that the P-horse and the domestic horse diverged from a common ancestor 500,000 years ago" ... "the only clearly distinctive difference between the two species was in the number of their chromosomes" ... "The P-horse has 66; the domestic horse, 64" ... "The close relationship, Lear said, "is reflected in the P-horse's ability to produce fertile offspring with domestic horses."

"If the wild horse mates with a domestic, the hybrid offspring will have only 65 chromosomes. But future generations will be back at 66 again."