ABOUT THIS WORKSHEET
This worksheet complements the Click and Learn “CSI Wildlife.” (http://www.hhmi.org/biointeractive/csi-wildlife).
As you proceed through the interactive, follow the instructions and answer the questions in the space provided.
- Read the introduction and watch the opening video.
- What is a keystone species?
When you pull the species out of the eco system, the whole thing stats to unravel.
- Wasser states that approximately 50,000 African elephants are killed each year. According to the video, it is estimated that there are around 470,000 African elephants. If these numbers are correct, approximately what percentage of African elephants are killed each year? (Show your work.)
470,000 – 50,000 = 420,000
420,000 ¸ 470,000 = .8936
.8936 x 100 = 89%
89% of African elephants are killed each year
- In one or two sentences, summarize Dr. Wasser’s research and how it is being used to conserve elephants.
Dr. Wasser is studying where the elephants are killed. He uses forensic tools based on DNA to pin point the elephant population to find out where the elephant ivory comes from. This allows them to find out where they are being killed so they can send law enforcement there to shut it down.
- Watch the crime scene video on the first slide of Case One. Explain the goal of the case.
One goal of the case it to find the origin of the ivory.
- Look at the map provided and list the region or countries the majority of African elephants inhabit.
Ivory Coast, Mali, Burkina Faso, Nigeria, Chad, Cameroon, Cabon, South Sudan, Kenya, Democratic Republic of the Congo, Angola, Zambia, Zimbabwe, and Nambia
Proceed to the How DNA Profiling Works section.
- What does “STR” stand for?
STR stands for short tandem repeats.
- Look at the gel on the screen. What do the bands on the gel represent?
The Left is a DNA latter made up of fragments of DNA of known lengths, the center and right are DNA fragments from two elephants.
- STRs at specific loci have shared characteristics between individuals and/or alleles. Place a check next to the characteristic(s) that are shared.
Made up of nucleotides
Unit, i.e., CTA
Same number of units
- DNA profiling is also called DNA fingerprinting. A common misconception about DNA fingerprinting is that the analysis has to do with actual fingerprints. Explain one similarity and one difference between a human being’s pattern of bands on an electrophoresis gel and a human fingerprint.
The difference is that the fingerprints are visible and are easily detected and the similarity is that they are both unique to each individual
- Click on Technique. List three sources to obtain elephant DNA for analysis.
Hair roots, saliva and body tissue
- Watch the animation on the polymerase chain reaction under Technique. Why are flanking sequences important for amplifying STR fragments?
Its important because it ensures that the regions between the bound primers are amplified
- A scientist makes primers specific to a particular STR fragment in elephants. These primers are then used to amplify the STR fragment from 10 different elephants. Would you expect the fragment to be the same size in all the elephants? Explain your answer.
No they would not be the same because all the elephants would have all different strands of DNA.
- Scientists typically amplify multiple STR fragments from an individual in a single PCR. Explain how they are able to do that.
They raise the temperature near boiling which causes them to separate into single strands. Next they use primers complementary to portions of the flanking sequences at different. This ensures that the regions between the bound primers, which include the repeat units, are amplified.
- What is the relationship between the size of a DNA fragment and the distance it migrates in the gel?
An electrical current is then applied to the gel, causing the negatively charged DNA to move toward the positively charged electrode. The longer the DNA fragment, the more slowly it moves through the gel.
- Why does DNA migrate to the positive electrode?
Because the DNA is negatively charged and the negative is attracted to the positive.
- Run the gel in the Technique section by pressing the Start Which elephant (left or right) has both the largest and smallest fragments? ___Left____________. Approximately what size is the largest fragment (bp)? 190__________ Smallest? _60________.
- Proceed to the Application section and look at the gel. For Marker C, are the two elephants in the gel on the left homozygous or heterozygous? How do you know?
They are heterozygous because there are two different bands that appear on the gel.
- These two elephants come from two different populations that are geographically distant from one another. If the gel were to show data from two elephants that were siblings, would their profiles be more or less similar? Why?
They would be more similar because they share more DNA
- Why do you think scientists use multiple markers to identify individual elephants?
Its less likely that the two individuals will have the same profile by chance.
- Complete the problems under the Review Show the equation you used to calculate the number of base pairs in the 10-repeat unit below.
8 repititions = 32 bp
10 repititions = x bp
X= 40 bp + 9 flanking sequence = 49 bp
- Sometimes PCR fails and instead of having two bands you end up with just one. The elephants represented in lanes 3 and 5 could have been a match to the ivory sample if you failed to amplify one allele in either the ivory or the sample, so you cannot exclude these choices without running the experiment multiple times. On the other hand, you can definitely eliminate the elephants in lanes 1, 2, 4, and 6. Explain why.
the pattern of the band won’t be the same in some parts and it varies causing errors during analysis, this is why several markers are used
- Watch the video on the “Case Solved” slide. Name two properties of a good marker and explain why good markers are important.
they point to different regions of the genome and it shows variation in DNA sequence
- How do you determine an allele’s relative frequency?
You determine it through the proportion of individuals that contribute a certain level within a population depending on whether they are haploid or diploid
- The gel shows a DNA profile of the elephant you identified in Case One. What is the relative allele frequency of the smallest marker fragment? ____0.09___________ Explain what this value means.
this means that within the specific marker the individual contains lower base pairs in their DNA
- The truck containing the ivory was equally distant from three different parks, so scientists calculated allele frequencies using the genetic profiles of elephant populations from just those parks. If they had no idea of the source of the ivory, they would have needed to calculate frequencies using genetic profiles from elephant populations throughout Africa. Why would a scientist choose one of these methods over the other?
A scientist should use this method because it could be said that it is based on speculation since they found the truck near three different parks.
- Looking at the calculation for profile probability, what does p2 represent?
It represents that the elephant could inherit a copy of his mothers DNA and a copy of his fathers DNA
- What does 2pq represent? Why is it important to “double” (multiply by 2) this frequency?
This represents a heterozygous elephant. Its important to double it because the elephant has 2 chances of obtaining the heterozygous genotype (one from his mother and one from his father)
- From the example, the homozygous frequency of the FH71 marker is 0.008 and the heterozygous frequency of the FH67 marker is 0.048.
- What is the heterozygous frequency of the FH127 marker? (Show your work.)
- What is the homozygous frequency of the FH19 marker? (Show your work.)
- Calculate the probability of an elephant having this exact DNA profile using all four markers. (Show your work.)
- Watch the crime scene video and read the Case Two introduction on the first slide. In Case One, you were looking for a match with an individual elephant. How does Case Two differ from Case One?
It differs because in case one we were trying to figure out what elephant the ivory came from whereas case 2 were trying to see where the ivory came from.
- Watch the short video in the “Building a Reference Map” section. Elephant populations differ from one another. These differences are due to geographic distance and the length of time since their ancestors separated from one another. Explain how this relationship affects their relatedness.
The relationship is effected because the researchers are trying to find a match for each ivory sample, using each elephant population to originate the ivory.
- Study the gel in the Building a Reference Map How does this gel differ from the gels you studied in Case One?
In case one, it showed that the alleles for an elephant was in several markers whereas in case 2 the lane has alleles for all the elephants within a population in one marker.
- In the gel under the Applications section, why does the ivory sample contain only two bands while the other lanes (samples A and B) have multiple bands?
It contains only two bands because they represent the DNA sequence whereas the other lanes represents a single population.
- If an ivory sample has two alleles that are also found in a population sample, does that tell you with certainty that the ivory sample came from that population? Explain your answer.
If the fragment sample has two different alleles in the DNA sequence then the allele could be found in two different populations.
- Answer the questions in the Review If the scientist had collected 20 dung samples, would you expect more bands, fewer bands, or the same number of bands on the gel? Explain your answer.
One would expect more bands because of the increase in the number of samples.
- Proceed to the Finding a Location Forest elephants and savanna elephants diverged over 2.5 million years ago, so some researchers think they should be classified as different species. Knowing this information, which genetic profiles would you predict would be more similar to one another: those of a forest elephant and a savanna elephant that are geographically close to one another, or those of two forest elephants that live far apart from one another? Explain your reasoning.
The forest and Savannah elephants would be more similar because the gel shows the alleles for the marker found in a sample of ivory found in these populations.
- The three populations of savanna elephants that were chosen for further analysis are geographically distant from one another. Why does this approach make more sense than choosing three populations that are geographically close to one another?
This will allow the alleles to be different populations which helps when identifying where the ivory comes from.
- On the Eliminating North, East, or South page, which population did you eliminate? ____North_________ Which marker(s) allowed you to make this choice? Marker FH48
- On the next page, which population did you eliminate? ___south__________ Which marker(s) helped you make this choice? Marker Fh60
- By analyzing many more markers and all the populations, Dr. Wasser linked these seized ivory tusks to which country? ______Tanzania____________
- Watch the video on the “Stopping Illegal Poaching” slide. Name two reasons elephant populations are threatened.
Economy and a lack of awareness
- Most of the ivory is bought by Asian countries, but the United States is the second largest market. Name two actions that you could take to reduce elephant poaching.
Protecting elephants natural habitats and implementing conservation laws
- In summary, elephants are a keystone species. Based on your knowledge of this term, explain in your own words why it is important to the ecology and ecosystems of Africa to save the elephant populations.
Its important because they have a role in the ecosystem by spreading seeds of plants to other places so the ecosystem can flourish.