A Matter of Selection

by Ryan Keeney

                1. The leaves of the Brassica oleracea definitely show the widest range of variation. Differences range in everything from color to size. For example, while our kohlrabi leaves measure only 12 centimeters from stem to tip, the collard and kale plant leaves have grown to over 20 centimeters each.


                2. There is a large amount of variation in domestic Brassica oleracea because each of the different variations has been created through selective breeding. Although the basic genes in the different subspecies of plants are the same, due to this breeding, certain alleles which control different phenotypes are favored over others. The first Brassica oleracea plants already had very small natural variations. Farmers would use artificial selection to accentuate these natural traits that already existed, depending on what they needed. For example, they may want to breed plants with a higher resistance for cold or an increased food yield. Through descent with modification, the different plants would slowly become more and more unique, with better versions of whatever traits are being bred for. Mutations also produce new traits which may also be seen as desirable, which can also be accentuated through natural selection.

                  3. A characteristic that is shared between all of the different subspecies of Brassica oleracea is the width of the stems. The stems of all of the plants are all around 1 centimeter thick, whether they are broccoli, kale, kohlrabi, or cabbage.

                  4.  If farmers wanted a plant to have larger leaves, which would increase food output, they would only allow plants with the largest leaves to breed, giving the offspring large leaves. Then, only the offspring with the most desirable characteristics would be allowed to breed, and this cycle would continue until the leaves reached the desired size.