Promiscuous Plants and Gene Flow

What does it mean to be a species? For animals, the definition is, loosely, a population that can interbreed and produce fertile offspring.

Horses and donkeys are considered separate species in this view, because although they can produce offspring, the mules so created are almost always sterile. Part of the issue is how fussy animals are about how many chromosomes they have. Horses have 64 chromosomes, donkeys only 62, so their offspring end up with 63. This causes problems when the chromosomes align and divide for reproduction, problems that are only very rarely overcome.

Plants, on the other hand, have a lot more genetic plasticity.

For example, they can produce viable offspring (who sometimes go on to become new species) with polyploid chromosomes, that is, twice as many (or more) sets of chromosomes as their parents. The development of polyploids can create food plants with larger fruit or vegetable parts. Think teacup strawberries.

While polyploidy doesn't, as far as I know, come into play in the genetically engineered food debate, you can see that such a thing obviously wouldn't work with animals, like us. A human with 48 chromosomes couldn't exist. Plants work differently and the rigidity of their species definitions works differently.

When someone buys a packet of seeds, those seeds have to be of the variety listed on the label. But though that variety may bear little resemblance to a wild relative, and even if the gene in question doesn't give the wild plant an advantage, the genes of the crop plant can become established in the wild population. How closely related would these plant relatives have to be? Not necessarily very closely.

Humans have been able to readily create plant hybrids between members of different genera. By the scientific biological classification system as it applies to animals, individuals of a different genus can be as or more different than humans and chimpanzees. Plants that distantly related can sometimes have viable offspring.

If plant reproduction weren't strange enough, it turns out that big missing pieces in evolutionary history were missing because bacteria can transfer genes between different organisms, or between different genomes within a cell. So the tree of evolution becomes more convoluted, because it isn't solely comprised of a logically spreading genealogy.

These are the things I think about when someone tells me that it's perfectly safe to release lab created plants into the wild for their synthetic genes to join this crazy mix. Because if there comes to be a problem that doesn't get discovered for decades, it will be too late to do much about it besides cross our fingers and hope it didn't contaminate anything important.

(Photo credit: marfis75 on Flickr.)