This spring, I noticed this striped flower in a stand of feral Hesperis matronis
Stripey flowers! And like almost all striped flower variants, almost certainly caused by transposons, aka jumping genes.
To understand transposons, you can think of genes as instructions. So when making a flower, a plant may be following a gene that says:
MAKE PURPLE PIGMENT
And so it does, and the flower is purple.
You can think of a transposon as a gene that says:
And so the cell makes a copy of the transposon, and then that copy gets dropped somewhere else in the genome. And sometimes, that new copy of the transposon lands in the middle of a gene that does something important. Like, for example, a gene involved in pigment production. So you get this:
MAKE PUR COPY ME! LE PIGMENT
Which doesn’t make any sense. So now the gene for making the purple pigment doesn’t work. And if that happens in a cell in a flower petal, that part of the flower will be white. And as that cell divides, the new cells resulting from it will also have the transposon in place, making more white cells, producing a white patch or stripe in the flower.
When transposons were first discovered in corn by the great geneticist Barbara McClintock, they were thought to be an oddity, something unusual. As we’ve learned more, it turns out they are ubiquitous. Some 40% of the human genome is thought to be transposons. Usually they are invisible, and have been silenced to prevent their moving around and disrupting other genes. But sometimes they pop up in a flower and make themselves visible, in a beautiful, interesting way.