Interpreting DNA Profiles
Bands in a DNA profile are similar to phenotypes because they
give an indication of the individual's underlying 
genotype.
They can be thought of as "alleles" which are inherited according to
the principles of Mendelian genetics. In this system, there are two
alleles: the "marker allele", which produces a band, and the "null allele"
which does not. It is not possible to tell whether an individual has
one or two copies of the "marker allele".
Every individual has an unique combinations of bands (or DNA profile)
which he inherited from his parents. Siblings also have distinct banding
patterns (DNA profiles) because they inherited different combinations
of bands from their parents. Only identical twins, which share the same
genetic material, have the same DNA profile. Unrelated individuals may
share some bands by chance (just as not all people with brown hair are
related). All bands present in a child's profile are inherited from
his parents. DNA profiles can be used to establish identity or paternity.
Steps to Determine Paternity
- Begin with the known parent. Assign the known parent a color, blue for instance.
- Color all of the known parent's bands blue.
- Look at the first nestling (n1). Color all of the bands from the nestling (n1) that exactly match a band from the known parent, blue.
- Look at the remaining adult individuals. Assign each one of them a different color, green and yellow for instance.
- Color all of an adult's band his/her assigned color.
- Look at the nestling's remaining bands. They must have been contributed by the second parent. Compare these bands to the remaining adult individuals. Find the adult which contains ALL of the remaining non-colored bands in the nestling's profile.
- Color the identifying bands in the nestling the same color as the second parent's bands.
- Repeat steps #3, 6 and 7 with the remaining nestlings.
Practice
This DNA profile is from a nest of captive Harris' hawks at the Arizona-Sonora
Desert Museum in Tucson, Arizona. Follow the steps described above to
identify the bands in the nestlings' profile which were contributed
by each parent. Use the Female (A) as the known parent.
You can now continue on to the other nests which all have three adult
birds. Remember to start with the known parent.
Directions: Please answer
the following questions in complete sentences.
- What problems might arise if the agarose wasn't dissolved
completely or if there were air bubbles in the gel?
- Why did you mix your DNA samples with a loading dye
prior to loading the samples into the gel? Give 2 reasons.
- What causes the DNA to travel through the gel?
- Draw a sketch of what your gel would have looked like
(after 5 minutes) if you reversed the positive and negative leads
and placed the positive lead closest to the wells. Label the
positive and negative leads, the wells, and the DNA.
- Why did we get a single large band at the top of each
gel when we loaded the DNA we had extracted from our cheek cells?
- Why does the lane with 1 kb ladder have several bands?
- Why do smaller DNA fragments travel further down the
gel?
- Study the gel below and answer the questions. Lanes
are numbered from left to right.
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- Why is the band in lane 2 thicker and darker than the
other bands?
- Why isn't there a band in lane 3?
9. Refer to lanes #5-7. Estimate the amount and concentration
of DNA in the following lanes; 5 uL of DNA was mixed with the loading
dye and added to each well:
- Lane 2: amount of DNA = _____ ng concentration of DNA = ______ ng/uL
- Lane 3: amount of DNA = _____ ng concentration of DNA = ______ ng/uL
- Lane 4: amount of DNA = _____ ng concentration of DNA = ______ ng/uL
DNA Analysis from Cheek Cells
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers
warder@email.arizona.edu
http://biology.arizona.edu/sciconn/lessons2/lessons.html
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