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Friday, April 29, 2011

Exploiting threes

Ever wonder how seedless fruits are propagated? Or for that matter, how could they come to be? A simple lesson in genetics is in order.

Most plants and animals of dietary consequence to us are diploids. That means that, like humans, they each carry two sets of their genetic material in their cells. When procreating, each parent has to make sex cells which carry only one set of genetic material - so that the progeny doesn't get a doubled set. This process of halving the DNA content is called meiosis, and is a system full of checks and balances. Should anything go awry, in most cases, the resulting sperm or egg cell is infertile.

So, if you want to make a seedless plant, you have to set up a situation where this process doesn't go as planned. One common strategy is triploidy.

The little black specks are the abortive seeds.
Unlike the diploid state, triploid organisms have three sets of the genetic material in their cells. This makes things simple - three just doesn't divide neatly into two. Consequently, triploid organisms tend to be sterile. Added bonus is that since there's one extra set of genes, many triploids produce bigger fruit than their diploid cousins. The most common example of a triploid is the banana. We take it for granted, but just about all commercial bananas are clones (the Cavendish), and they are propagated as such because they can't make seeds. Diploid bananas do exist, and they are so chock full of peppercorn sized seeds, you'll have a hard time eating them - and they are so much smaller than the Cavendish, too.

Not to say that triploidy can only be applied to plants. One of the animals that we take advantage of triploidy in: oysters. Unable to make viable sex cells, the decreased gonad sizes mean that triploid oysters become larger and devote more their resources making, well, themselves. Think of them as molecular eunuchs.

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