Inheritance System of anthocyanin pigments in Brassica rapa. Introduction The observations of Brassica rapa in class revealed a variation in color. Brassica rapa, also called fast plants, was studied because as their name suggests, they are able to complete a lifecycle in a short period of time. (www. fastplants. org) The color variations we observed among the plants were that some had green stalks while others were purple. The pigment which gives plants their color is called anthocyanin. (www. carnivorousplants. rg) Anthocyanin is responsible for the variety of colors seen in plants. The anthocyanin pigment serves two purposes for plants. Plants use the color to attract insects to facilitate reproduction. The pigment also serves as a sun block, protecting the plants DNA from UV damage from the sun. What was the inheritance system for the differing pigmentations? Was green the dominant allele or was purple the dominant allele? Or does Brassica rapa exhibit incomplete dominance which would result in a brown colored pigment?
An experiment was needed in order to determine how the pigment was inherited. It was expected that if the allele which provided the green pigment was dominant than all the F1 generation would be green. Alternatively, if the allele which is responsible for purple is dominant, than all the F1 plants should be purple. If the plant exhibited incomplete dominance than the F1 generation should all be brown, a hybrid of purple and green. (Biology) Once an F1 generation was produced, we could then crossbreed to see what phenotypic ratios the F2 Brassica rapa exhibited.
If green pigmentation was dominant, we could expect to see a 3:1 ratio of green to purple plants. If purple pigmentation was dominant, we would see a 3:1 ratio of purple to green. If there was incomplete dominance between green and purple alleles, a ration of 1:2:1 of green:brown:purple would be expected. Method The experiment consisted of eight seeds of true breeding green and eight seeds of true breeding purple plants being grown in a planter. The plants were all maintained at the same temperature and given the same amount of water.
They were all exposed to fluorescent lighting for 24 hours a day. Once the true breeding green and purple plants flowered, which occurred in about 14 days, we cross pollinated them and waited about 16 days for the F1 generation to germinate. When the F1 generation flowered, we again cross pollinated the plants but this time we pollinated only among the F1 generations. When the F2 generation bloomed and produced seeds, about 40 days time, we separated the seed pods into a Petri dish and observed the coloration when the seeds germinated.
At this point we were able to look at our data and see what kind of inheritance system was exhibited by Brassica rapa. Results In our group, 35 out of 40 seeds from the F2 generation sprouted. 19 of the sprouts were purple and 16 were green. The entire class, including our group, had a total of 240 spouts. There were a total of 139 purple and 101 green. Discussion and Conclusion What did the results tell us about the inheritance system of anthocyanin pigments? We could rule out an incomplete dominance system as there were no brown sprouts.
While we hypothesized a ratio of 3:1 in favor of the dominant allele, we instead had a ratio that was almost 1:1. When we completed a chi-square test to see if we did indeed have a 1:1 ratio, our p value was less than . 05 and we had to reject the 1:1 ratio. The ratio which we ended up with was different than what we hypothesized we would see. It’s possible that the samples were contaminated, or perhaps the true breeding seeds we had started with had not been sorted correctly at the factory. There could have been some cross pollination which happened outside of our control.
There could have been a miscount in the number of sprouts and their color by one of the groups which threw off the p value. And it’s quite possible that 240 sprouts are too small a number of sprouts to make up a sample study. Even though we cannot control the seeds which we receive from the factory, a new experiment could be set up which would mitigate the concerns brought up above. References Biology 7th Edition, Campbell & Reece. Chapter 14 http://www. fastplants. org http://www. carnivorousplants. org Science 9/1998 Sullivan, Jack