It's true that sexual reproduction shuffles genes, and this
contributes to diversity in the sense that it produces new combinations
of genetic material. Even self-pollination achieves this. However, a
diploid organism will generally only have two copies of a particular
gene, while a wild stand of a particular species could have countless
genetic variations. I think the risk in relying on captive plants for
reintroduction of a species in the future is, in an overly general and
simplistic sense, two-fold: 1. We do not understand what traits the
plants will need to survive upon reintroduction, and we may be selecting
against those traits inadvertently in cultivation and 2. Once the
original habitat is lost, we have lost not only our favorite plants in
the wild, but all the other microbes, plants and animals that grew with
them but weren't deemed "cool" enough for anyone to bother preserving.
As for transposable elements, which I assume are the jumping
genes you're refering to, I don't see how they contribute significantly to
diversity. True, they can be mutagenic when they insert into genes and
thereby knock out those genes, but this is rarely beneficial to the plant.
They do not typically carry host genes with them when they move, so they
aren't really jumping plant genes to new locations. Even if they
did, this isn't really contributing to genetic diversity.
> I'm reminded of the story of the 30 British starlings that were
> released in New York (I think in the 1930's). They're now a pest and
> are found all over the United States, much to the consternation of our
> American blue bird. The genetic diversity of those 30 starlings was
> enough to ensure the survival of the species in the US. My impression
> is that the diversity within a plant is much greater than the
> diversity within a bird.
I think Michael Chamberland adressed these points very nicely,
and I won't add anything to his response.
Wayne Forrester