Student Blog Post Assignment #9: A Matter of Selection

The characteristic of the Brassica oleracea that shows the greatest variation is the shape of each variety' leaves. Many of them are similarly colored, but they exhibit many different forms and lengths. The characteristic of the Brassica oleracea that exhibits the greatest range of variation between extremes is their height. While the average height of the cabbage is only 10 inches, the average height of the broccoli plants is 42 inches. While many fit in a small range of height, the broccoli is literally four times the height of the rounded cabbage plants.

	Cauliflower	Kohlrabi	Kale	Cabbage	Collards	Broccoli	Brussels	Romanesco
Height inches	25	21	24	10	16	42	15	32

The reason there is so much variability in the domesticated forms of Brassica oleracea is that as they have become more common in the farming world, certain, more helpful genes have been selectively bred to produce more productive plants. This is called artificial selection; some farmers choose only to breed plants with the desired traits so as to pass on those traits and not others. Based on where each variety is being grown, it is going to be helpful to have different traits, so humans modify there Brassica to fit their growing needs. In addition, some mutations will appear over time. More effective ones will stick around and affect the plants for longer. Sometimes the plants will be affected by dissent with modification. Parent plants will pass on their traits but not in the exact form; the traits will be modified. All of these things affect the Brassica oleracea over time.

The feature of the Brassica Ocelerae that appears to be the most consistently the same is the color of the plants' leaves. While the shape varies quite a bit between each variety, the vast majority of the plants' leaves are a similar sage green. Kale's leaves are slightly darker and cabbage leaves are purple but the rest are very similarly colored. This is most likely because the chlorophyll in the plants has a green pigment. Because the plants are the same species, they most likely have similar levels of chlorophyll. This is why their coloring is the same. The purple color of the cabbage leaves is most likely due to a mutation that stuck and the kale is probably just a slight variation in the chlorophyll.

In order to increase diversity in leaf color among Brassica Oleracea, farmers would need to only let the extremes breed for each variety. If for instance, you wanted to make the average shade of Kohlrabi leaves darker, then you would breed only the Kohlrabi plants with the darkest leaves and ignore the ones with lighter pigments. That way over time the lighter leaved plants would die off and the number dark leave plants would increase, in addition the degree of darkness of the plants.