Which has more DNA, Plants or Animals?

[vasan]

My son is in the 4th grade and he has chosen to do a project on DNA extraction. At first we were just doing a simple extraction experiment from strawberries and other foods. But when I got back with his teacher he wanted there to be graphs in the results displayed. So we decided that we would not just extract but also weigh the DNA extracted to be able yo compare the data. We have then come down to this title. Which has more DNA, plants or animals? The sample for plants would be strawberries and the animal sample would be chicken liver. We plan to use detergent, salt, water, alcohol to extract and isolate the dna. The plan is to remove the dna from the container witha popsicle stick and weigh the dna on the stick. We have not actually performed the experiment. What do you think is there any thing we have overlooked ? Project is due next week. Also could you give us any ideas on resource material on this project.

[donnahardy2]

Hi,

I think you are doing this excellent project from the Science Buddies website:

Hi Vasan,

Welcome to Science Buddies! I think your son is doing this really good project from this website. The background section includes a basic description, some terms and concepts, and one reference that you can review with you son:

http://www.sciencebuddies.org/science-f ... p001.shtml

Here are two sites that discuss the difference between plant and animal DNA and the difference between bacterial and plant/animal DNA, respectively. Don’t worry if you son doesn’t understand everything at this point.

http://www.ehow.com/about_6791106_diffe ... plant.html

http://www.sciencebuddies.org/science-f ... eityourown

http://curiosity.discovery.com/question ... ant-animal

Here is an abstract of a science fair project on a this subject. .

http://www.usc.edu/CSSF/History/2008/Projects/J0415.pdf

Your idea to compare the quantity of DNA from different samples is a good idea. The key to doing this experiment will be control all other conditions except the sample. For example:

1. Use the same weight of each sample
2. Weigh the popsicle stick for each sample before you the collect the DNA.

Ask your son if he can think of any other parameters that should be controlled.

I recommend doing each sample in duplicate.

I recommend display results in a bar graph.

http://nces.ed.gov/nceskids/createagraph/

http://www.sciencebuddies.org/science-f ... ysis.shtml

Your son has very little time to complete this project so he should start writing sections for the display board. Be sure the read the teacher’s assignment and include any details that are required. Here are all of the sections required for a display board:

http://www.sciencebuddies.org/science-f ... oard.shtml

Please post again in this topic if there are any other questions.

Donna Hardy

[vasan]

Thank you for your reply. I was mistaken about the dates. He had to submit a progress report the following week but the final display isn't due till 2/27. Very sorry. He did do the experiment already. He controlled all the ingredients. All items were weighed to 75 gms. alcohol ,salt, detergent and water were all pre-measured and consistent. he did the experiment with strawberries, chicken liver, beef liver and kiwi. beef liver was 1st , strawberry was 2nd, chicken liver was 3rd and kiwi was 4th. he had a problem then because his hypothesis was that animals had more dna than plants. so he did another 5th experiment with sweet peas. after this final experiment the results were beef 1st, starwberries 2nd, chicken liver 3rd, peas 4th and kiwi 5th. so his conclusion was that animals has more dna except for strawberries which came in between beef and chicken because strawberry is a special fruit. We know that strawberry is an octoploid but he needs to look up some resource to prove that since he can't just mention it after reading this website. What would be a sound and good resource to prove that strawberries are octoploids? Thank you for your input

[vasan]

I love the website you posted on the graph. He will surely be able to do the graph on his own using this. At this point actually he's so confused about how to present his conclusion. I don't think he would have been able to take 2 samples of each item as you recommened. It is his 1st science project and I feel he has chosen a heavy topic. I wish the results would have been easier to explain but now with the strawberry in between he is sort of stuck on how to word his results. Any input would be appreciated.

[donnahardy2]

Hi Vasan,

It sounds like your son did a great job and obtained quantitative results. He had a reasonable hypothesis and he did a controlled experiment, however, he did not confirm his hypothesis. There is nothing wrong with this and it is very common with science projects and with experiments done in research labs.

Your son should go ahead and prepare his bar graph. The results are empirical; they are actually what happened. Be sure the graph is labeled completely. The graph should be the centeripeice of the display board.

He really can’t say that animals have more DNA than plants because of the results of the strawberries. What about all of the plants and animals he did not test? The best thing to do is to do some additional reading and try to do a thoughtful analysis that will explain the results. Your son should start his conclusion section by saying that his hypothesis was not correct, that animals do not have more DNA compared to plants. He can then distinguish his project with his discussion section. Here are some ideas:

Here is a website that lists the number of chromosomes for various species. Please note that the list contains a mixture of plants and animals, and there does not seem to be any trend in the numbers. Rats and ferns are at the top of the list and rye and mosquitoes are close to the bottom of the list.

http://en.wikipedia.org/wiki/List_of_or ... some_count

Why don’t you help your son do a search for the number of chromosomes for each of the species tested? Perhaps there is a correlation between his results and the number of chromosomes?

Did your son do duplicate results on his samples? If so, were the results reproducible? If he did not run duplicate samples, then it’s possible that the normal variation in results from this experiment caused the variation. So the cause would be normal experimental error.

If the results are still not explainable, ask you son if he can think of anything else. Your son can also include a suggestion for another experiment that he might do in the future that would explain his results.


Donna Hardy

[vasan]

Hi Donna,

Love your inputs. Thanks so much. He had to accept that his hypothesis was wrong. We went through the internet looking for any correlation between the number of chromosomes and his results but they were not in any way showing any correlation. However, as we were reading your first reply again, there was a webiste with some information you had given on "differences between plant and animal dna extraction". The idea was cell walls. He concluded that animals were easy to extract because they have no cell walls but because plants have cell walls they are harder to extract from with the exception of strawberries because it has thinner walls than kiwi and peas.

[donnahardy2]

Hi Vasan,

Thanks for your feedback. Your son's project sounds like it was excellent, and the fact that the hypothesis was not confirmed will not detract at all from the scientific merit of the investigation. Science fair judges look for the hypothesis, the data, and the conclusion and make sure there is some correlation, and your son's project was absolutely correct.

Donna