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DNA Extraction from Fruit
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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Update: June 2012
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