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Name: Danbi
Status: Student
Grade:  6-8
Location: NY
Country: United States
Date: April 2005


Question:
I was just curious and was really interested in DNA extraction and I am just wondering about this one thing that I wanted to ask. Does the difference in sets of chromosomes affect the DNA extraction? For example, the bananas have triploid sets of chromosomes and kiwi has diploid sets of chromosomes.. so does that mean from equal amount of those two fruits, a banana has greater amount of DNA extracted if I do extract DNA from both fruits? And also what are differences between triploid and diploid sets of chromosomes?



Replies:
It is not only the *number *of chromosomes in a cell that determines the amount of DNA in a cell but the length and thickness of the chromsomes. There are several species of amphibians and plants that have more DNA per cell than human cells. There is just no way of predicting the amount of DNA in a cell based on just the number of chromosomes. Some species are polyteny meaning they have multiple parallel copies of genes in a single chromosome, for example, the salivary glands of fruit flies (*Drosophila melanogaster*) have 1024 copies of the same strand of DNA in each of the 8 chromosomes in these cells.

Ron Baker, Ph.D.


What a great couple of questions!! It really lets me know that you're grappling with what is happening with the molecules responsible for heredity, and I know that that has got to be quite a leap. So, let's take the questions bit by bit.

Does the number of chromosomes in a cell have an impact on the amount of DNA extracted from the cell? Your example presented a diploid and a triploid, meaning two sets of chromosomes and three sets of chromosomes. And what I want you to understand is that you've focussed on a characteristic of the genetic material that has everything to do with how the mechanism of heredity works (how the genes are passed from generation to generation joined together on one or another chromosome, therefore more likely inherited together if on the same chromosome or less likely inherited together if on separate chromosomes), but very little to do with how much genetic material may be in each cell. If the chromosomes in the two species you mentioned were about the same size, meaning that the amount of DNA in a haploid of each species were about the same, then taking equal numbers of cells of the diploid species and the triploid species should result in a 50% increase in DNA extracted from the triploid as compared to the diploid species. So, you'd need to know how the haploid (i.e., single) set of chromosomes in one organism compared to the haploid set of chromosomes in the other organism.

And as to the difference between the triploid and the diploid sets, as indicated above, you'd have three sets of chromosomes and two sets, respectively. In the typical diploid, there will be one set of chromosomes from the father and one set of chromosomes from the mother, resulting in a fertile offspring. The triploid common in the banana is what makes the banana seedless.

Thanks for the question!

D. Silvert



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