Hmm...4 N vs. 3N vs. 2N..
You know, a mule is a cross between a horse and a donkey. Horses and donkeys don't have the same number of chromosomes, so mules are sterile. This sterility is due to the fact that there is a differing number of chromosomes. Donkeys have 62 while horses have 64.
There is a chemical that can cause the usual number of orchid chromosomes to double, resulting in a plant that has twice the number of usual chromosomes; therefore 4N (a 2N plant has the normal number of chromosomes). These 4N plants are back crossed with 2N plants resulting in 3 sets of chromosomes (2N). These chromosomes can't pair up normally so a 3N plant is sterile.
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I took a taxi from LA to Venus in 1985.
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