A Matter of Selection-Whitley Moody

For B1.  My team and I observed all of the Brassica oleracea plants in our garden. We saw the greatest variation between the different leaves from the plants.  They were not only multiple different textures, but different colors, sizes, and smells.  We found at least ten leaves that looked completely different than the ones before them.  Below is a picture of a few examples of the leaves.

We saw the greatest range of variation in the height of the plants.  We went out into our garden and measured the height of all of our plants using a meter stick.  For being the same species, there was an extreme change from the height of the smallest fully grown plant and the largest fully grown plant.  The smallest fully grown plant had a height of 12cm, while the largest fully grown plant had a height of 72cm.  In the pictures below you can see the variety of heights displayed by the plants.  

2.  There are many reasons why there is so much variability in domestic forms of Brassica oleracea. First off, farmers have performed artificial selection and selective breeding.  Those processes allow the farmers to pick and choose which specific traits new generations of the plant will receive.  This allows them to create a new plant that might be completely different from it's mother and father plant, yet still be a part of the Brassica oleracea species.  Another way that multiple different types of Brassica oleracea have developed over time is through a process where natural variations are created.   These variations happen when mutations occur to the cells of the plants in order for them to be able to survive in their environments.  Mutations occur in the genes of the plants by deleting or adding alleles.  After both artificial selection and the process of creating natural variations happens, descent with modification will pass the genes for specific traits on to the next generation.  

3.  The part of the Brassica oleracea plants that seems to be the same in all of the examples in our garden is the fact that all of the plants originate from the Wild Cabbage plant.  Every single plant has a part that can be traced back to that plant.  I think that this happened because the species had to start with a single organism, and then it mutated and changed over time.  

-For Kohlrabi, the stem was modified from the original plant.

-For Kale, the leaves were modified from the original plant.

-For Broccoli, the stem and flower buds were modified from the original plant.

-For Brussel Sprouts, the lateral leaf buds were modified from the original plant.

-For Cabbage, the terminal leaf bud was modified from the original plant.

-For Cauliflower, the flower buds were modified from the original plant.

Clearly, all of the different plants that branch off in the Brassica oleracea species can be traced back to the Wild Cabbage plant.  Over many years, natural selection and/or artificial selection must have occurred in order for the new plants to have been made.

4. Well, since I focused on how each plant originates from the Wild Cabbage plant, in order to drastically change how each of the plants are now, plant breeders would need to continue to artificially change each new plant generation.  This would be extremely difficult because there would be a point where the plants would be unable to be engineered further.  The breeders would reach a limit on how they could change the plants.