Think of Footprints
How does this work? Think of yourself standing in a field covered by an inch or two of fresh, untouched snow--or perhaps in front of the smooth, wet sand closest to the water on a favorite beach--before anyone else has had a chance to walk there.
If you decide to be the first to walk on this field of snow or on this smooth, wet sand, you'll disturb it by changing its appearance with your footprints! The change may seem minor, but it's still a change. In the case of the snow field, the spots marked by your footsteps may be the first to melt if no one else goes into that field.
What's That Got To Do With Grapes?
The jumping gene that causes the color mutation in grapes was named "Gret1."
“When Gret1 ‘visits’ and then leaves parts of the gene, it slightly changes the surrounding material, like the footprints in the snow," says Owens. These changes make the VvmybA1 gene slightly different--and different enough to affect the color of the grape.