Whales have undergone very large physical changes in their recent evolutionary past. This makes comparisons with other mammals difficult. It also makes understanding their evolutionary kinships particularly challenging. However, genetic sequences are now providing biologists with powerful new tools for revealing evolutionary relationships. One potentially ideal type of genetic sequence is known as a SINE (short interspersed element). In this investigation you will use the presence of SINEs to construct a cladogram and infer the evolutionary relationship of whales to some land mammals.
Purpose
To use the presence of SINEs to investigate the evolutionary kinship of whales with cows, giraffes, hippopotamuses, and pigs
Predictions
Make the following two predictions:
- Which of these species do you suspect whales are most closely related to? - Which of these species to you think whales are least closely related to?
Procedure
Background: SINEs are sequences of DNA (more than 100 bases long) that have become inserted into a chromosome at random during a viral infection. Because the DNA molecules in chromosomes contain millions of bases, the chances of two identical SINEs getting inserted into the same location in many different individuals is extremely remote. If all African elephants, for example, have the same SINE at the same position on chromosome #9, we can conclude that all African elephants inherited this SINE from a common ancestor. By extension, if every Asian elephant also has the identical SINE in the same position on their chromosome #9, then we can assume that the SINE was found in an individual that was an ancestor to both Asian and African elephants.
1. Use the information in Table 1 to construct a cladogram showing the phylogenetic relationships between these five species. Note: Each of these SINEs can be considered a recently derived trait.
Table 1
Species: cow SINEs: A: + B: + C: - D: +
Species: pig SINEs: A: - B: - C: - D: +
Species: fin whale SINEs: A: - B: + C: + D: +
Species: giraffe SINEs: A: + B: + C: - D: +
Species: hippopotamus SINEs: A: - B: + C: + D: +
Species: camel* SINEs: A: - B: - C: - D: -
*The camel is the outgroup.
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2. Your cladogram should include the letters A, B, C, and D at positions indicating when each of these SINE insertion events may have taken place.
3. Also include the label MRCA to indicate the position of the most recent common ancestor of whales and their most closely related species.
Analyze and Evaluate
(a) Were your predictions correct? To which species are whales most closely related? To which species (ignoring the outgroup) are they most distantly related? K/U
(b) Which SINE insertion occurred first—A or B? Explain your reasoning. K/U
(c) Are pigs more closely related to camels or whales? How do you know? K/U
(d) What SINE(s) would you expect to find in all giraffes? What SINE(s) would you never expect to find in giraffes? K/U
Apply and Extend
(e) Imagine a geneticist discovers a new matching SINE in DNA samples from a hippopotamus and a cow. Predict the results of looking for this same SINE in DNA samples from each of the other mammals. T/I (f) A new SINE is discovered in the pygmy hippopotamus but not in the closely related common hippopotamus. Do you think it would be possible to find this same SINE in whales? Explain your reasoning. T/I
(g) Imagine you are describing the results of this investigation to a fellow student. You explain that, when tested, a number of hippopotamuses, whales, cattle, and giraffes all had the same SINE insertion B in matching positions in their chromosomes. The other student suggests that this is not evidence of evolution, but simply evidence that these animals had each been infected by the same virus. Is this a strong alternative hypothesis? Why or why not? T/I A
OBSERVATIONAL STUDY
SKILLS MENU
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Looking for SINEs of Evolution
Whales have undergone very large physical changes in their recent evolutionary past. This makes comparisons with other mammals difficult. It also makes understanding their evolutionary kinships particularly challenging. However, genetic sequences are now providing biologists with powerful new tools for revealing evolutionary relationships. One potentially ideal type of genetic sequence is known as a SINE (short interspersed element). In this investigation you will use the presence of SINEs to construct a cladogram and infer the evolutionary relationship of whales to some land mammals.
Purpose
To use the presence of SINEs to investigate the evolutionary kinship of whales with cows, giraffes, hippopotamuses, and pigs
Predictions
Make the following two predictions:
- Which of these species do you suspect whales are most closely related to?
- Which of these species to you think whales are least closely related to?
Procedure
Background: SINEs are sequences of DNA (more than 100 bases long) that have become inserted into a chromosome at random during a viral infection. Because the DNA molecules in chromosomes contain millions of bases, the chances of two identical SINEs getting inserted into the same location in many different individuals is extremely remote. If all African elephants, for example, have the same SINE at the same position on chromosome #9, we can conclude that all African elephants inherited this SINE from a common ancestor. By extension, if every Asian elephant also has the identical SINE in the same position on their chromosome #9, then we can assume that the SINE was found in an individual that was an ancestor to both Asian and African elephants.
1. Use the information in Table 1 to construct a cladogram showing the phylogenetic relationships between these five species. Note: Each of these SINEs can be considered a recently derived trait.
Table 1
Species: cow
SINEs:
A: +
B: +
C: -
D: +
Species: pig
SINEs:
A: -
B: -
C: -
D: +
Species: fin whale
SINEs:
A: -
B: +
C: +
D: +
Species: giraffe
SINEs:
A: +
B: +
C: -
D: +
Species: hippopotamus
SINEs:
A: -
B: +
C: +
D: +
Species: camel*
SINEs:
A: -
B: -
C: -
D: -
*The camel is the outgroup.
Print Page 368
2. Your cladogram should include the letters A, B, C, and D at positions indicating when each of these SINE insertion events may have taken place.
3. Also include the label MRCA to indicate the position of the most recent common ancestor of whales and their most closely related species.
Analyze and Evaluate
(a) Were your predictions correct? To which species are whales most closely related? To which species (ignoring the outgroup) are they most distantly related? K/U
(b) Which SINE insertion occurred first—A or B? Explain your reasoning. K/U
(c) Are pigs more closely related to camels or whales? How do you know? K/U
(d) What SINE(s) would you expect to find in all giraffes? What SINE(s) would you never expect to find in giraffes? K/U
Apply and Extend
(e) Imagine a geneticist discovers a new matching SINE in DNA samples from a hippopotamus and a cow. Predict the results of looking for this same SINE in DNA samples from each of the other mammals. T/I
(f) A new SINE is discovered in the pygmy hippopotamus but not in the closely related common hippopotamus. Do you think it would be possible to find this same SINE in whales? Explain your reasoning. T/I
(g) Imagine you are describing the results of this investigation to a fellow student. You explain that, when tested, a number of hippopotamuses, whales, cattle, and giraffes all had the same SINE insertion B in matching positions in their chromosomes. The other student suggests that this is not evidence of evolution, but simply evidence that these animals had each been infected by the same virus. Is this a strong alternative hypothesis? Why or why not? T/I A