Blog Post #8 by Clare Robke

A Matter of Selection 

Since the start of the school year, my team and I have had the eye-opening opportunity to plant and observe our very own Brassica oleracea, or broccoli, plants in the garden. Throughout the experience with our own plant, we have also been able to witness many other types of Brassica oleracea grow and mature to develop different traits at every stage of their life cycles. Despite the fact that all 4 types of plants growing in the garden (broccoli, cabbage, kale and cauliflower) share 99% of the same DNA, upon close observation and data collection it is clear that, along with the obvious similarities, there are also notable differences and variation present among the organisms. 

During our investigation, we discovered that the characteristic of the plants that exhibited the most variation (greatest number of different forms) was the leaf shape and size. Some of the plant leaves were round and floppy, while others were more ridged with a lot of indentations. And the size in all of them varied greatly as well, with the average length ranging from over 19 centimeters to 12 centimeters, and the average width ranging from 15 centimeters to just 8 centimeters. We collected our data by looking at and measuring the leaves, specifically those that seemed to be the most average, best representation of that specific plant group.

The above image shows the length and width of every plant measured as well as the average for each of those measurements. 

Here you can see the length of one of the broccoli leaves as well as the process by which we measured. The length of this leave was 17 centimeters and the average length for broccoli was 17.67 cm.

This image shows the width of the same broccoli leaf to be 8 centimeters, which also happened to be the average. That shows how we collected data from plants that represented the majority of the plant types.

The images to the left and right show the length and width of one of the kale leaves. The average length for kale leaves was 13.67 cm. and the average width was 10.33 cm.

This picture shows the length of a cabbage leaf. The average length for cabbage leaves was 12.33 cm.

The above photo shows the width of one of the cabbage leaves we measured. The average cabbage leaf width was 9.67 cm.

Above and below are pictured the length and width of a particular cauliflower leaf. Cauliflower plants had the overall biggest leaves, with the average length being over 19 cm. and the average width being 15 cm. 

Throughout our data collection from the various forms of Brassica oleracea, it was immediately clear to us, as it would be to anyone who just took a look around at the garden, the great variability in the domestic forms of the species. Variability is just a fancy way of saying different, or not in a fixed pattern, and based on the images and measurements I have shown, this characteristic of the organisms is obvious. But as to why their is such variability in all the plants' traits, I believe it has something to do with humans and artificial selection as well as adaptations and natural selection. With the technology and agricultural knowledge that humans have today, we are able to develop organisms with specific desired traits that we want them to possess for some purpose that will benefit us. This is called artificial selection, which makes sense because it is kind of like natural selection, except humans are in charge of which traits get passed on rather than mother nature. One of the ways humans can control this is by selective breeding. It's pretty self-explanatory: we pick specific males and females of the same species with the "best" traits and make them reproduce to pass down the desired genes to their offspring who will then pass them down to their offspring and so on. This process of passing down the new genes is called decent with modification. This human interaction affects our Brassica oleracea because the diversity we see in its different forms likely comes in part from years of farmers selectively breeding plants with specific phenotypes to create different offspring for different purposes. Another factor that contributes to the variability we see in our garden is much more natural. In order to get natural variations of our Brassica oleracea, like our cabbage, broccoli, kale, and cauliflower plants that all taste very similar and can reproduce, but also have some differences, the plants must adapt to different environmental factors. For example, the cauliflower leaves are significantly larger than any of the other leaves, but otherwise look pretty similar to the broccoli leaves. This could be because a group of broccoli plants were growing among many other plants so they needed to adapt and grow larger because they were in competition for sunlight. Eventually, after many years of the broccoli growing larger and passing that trait down to offspring, the broccoli was no longer broccoli, but cauliflower. That is just one example of how nature creates variety. Another natural way is mutations. A mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene. Some mutations can harm or hurt and organism, or not affect it at all. They can also code for a different amino acid, which can create some noticeable differences in the phenotype of the organism, like we have witnessed in the different Brassica oleracea. I believe that a combination of man-made and natural factors have all contributed to the variability we see in Brassica oleracea today.





Despite the variation of traits and variability we have been discussing, all of the Brassica oleracea do share 99% of their DNA so they also have many similarities. Upon looking closely at all the plants, I discovered that the part of the plants that was most consistently the same throughout the garden were the flowers. All of the flowers were a bright yellow color, had roughly the same number of petals, and grew in clumps at the end of the stem. My teammates and I agreed that the flowers were so similar that it would be hard to tell the plants apart if we only looked at their flowers. I think the flowers are probably the most similar because they are the reproductive part of the plant, and because the plants can reproduce with one another and share so much of their DNA, their reproductive parts would need to be pretty alike.

 The following images are the flowers from the four different plants (broccoli, kale, cabbage, and cauliflower). The resemblance between all of them is quite apparent, which is why I chose them as the part of the plants that were most consistently the same.

In order for plant breeders to get the flowers of the Brassica oleracea mentioned above to become much different than they are currently, they would need to identify which of the flowers' traits they want to modify and find some plants that exhibit that phenotype. Then, they would need to grow the plants with the desired traits in close proximity with the other regular flower plants until they begin to reproduce and pass on the desired trait to more and more generations until a natural variation results, like we see in the different leaves and stems of the plants. Another possibility to change the flowers would be to grow the plants in conditions where the flowers must adapt. For example, if a certain pollinator, like a bee, is more attracted to purple flowers than yellow, the breeders could start growing some broccoli in an area where bees are the only possible way to be pollinated. The flowers would be forced to adapt in order to survive. This combination of artificial and natural selection is another way to alter the genes of the plants.