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Name _ _ Class _

Evidence of Evolution: Comparative Anatomy Lab

INTRODUCTION: Evidence has been found to indicate that living things have changed gradually during their natural history. The study of fossils as well as embryology, biochemistry, and comparative anatomy provides evidence for evolution.

OBJECTIVE: In this lab activity you will learn about homologous, analogous, vestigial structures, fossils, embryology and biochemistry and their significance in evolution theory.

Station 1: Homologous Structures

There are many examples of body structures that are formed in similar ways during embryonic development and that share similar patterns of bone structure, even though they take on different forms and perform somewhat different functions. These structures are called homologous structures. Homo- means same, and -logous means information, so homologous means “same information”. Homologous structures mean that the animals share a relatively recent common ancestor.

1. Carefully examine the drawings of forelimb skeletons shown in Figure 1 on the next

page. Look for similarities in the bones amongst the various animals.

2. Color in the human arm first. Color the bones of the arm (the humerus, ulna, and radius) blue. Color the bones of the hand (the carpal, metacarpals, and phalanges) yellow.

3. Color the corresponding bones in each of the other animals the same color as the

human bones.

4. Observe each of the skeletons again, and describe the function of each limb in the table below:

Animal Function

human

whale

cat

bat

bird

crocodile

5. Answer the Summary Questions.

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Figure 1.

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HOMOLOGOUS STRUCTURES

1. Are the functions of the limbs of each of the animals illustrated the same or different?

2. Are the bones of the limbs arranged in a similar or in a very different way in each animal?

3. Does the similarity in bone structure suggest a common ancestry amongst these animals?

4. Offer a possible evolutionary explanation for how the skeletons can be similar but the functions very different in each of the animals.

5. Are the bones arranged in a similar way in each animal?

These structures are formed in similar ways during embryonic development and share like arrangements: however, they have somewhat different forms and functions. They are called homologous structures.

Station 2: ANALOGOUS STRUCTURES

There are also many examples of body structures in animals that are very similar in function and superficially similar in form and but develop very different and have very different internal structures and embryonic development. These structures are called analogous structures. Analogous structures mean that the animals do not share a recent common ancestor.

6. Examine the butterfly wing and the bird wing shown below.

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7. Look for any similar bone structure.

8. What function do the butterfly and bird wings share?

9. In what way do these structures differ?

10. Can you think of a possible reason why two unrelated species have the same way of getting from place to place?

______________________________________________________________________________________ ______________________________________________________________________________________

11. Do birds and insects share any structural similarities that would suggest they are closely related? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________

Some apparently unrelated animals have organs with similar function, yet are very different in structure and form. These structures are called analogous structures.

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Station 3: Vestigial Structures

There are also many examples of body structures in animals that show gradual changes over time. In some cases, these changes have reduced or removed the function of some body parts and organs. These reduced or lost structures are called vestigial structures. The wings of penguins and the leg bones of snakes are examples of this phenomenon.

12. Observe the drawings of the cavefish and the minnow shown in Figure 3. The fish are

related to each other but the cave fish is blind and only has the remnants of an eye.

13. Explain why eyesight is not an important adaptation to life in a deep sea cave.

14. Does the appearance of the cavefish and the minnow suggest a common ancestry? Why?

15. Read the list of human vestigial structures shown below. Suggest a possible function for each structure and explain why it became vestigial:

16. List another structure (not listed in this lab) that you think is vestigial and explain why.

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VESTIGIAL STRUCTURES

Structure Probable Function Why Vestigial?

appendix

Possible raw meat digestion? Discovery of fire? We started cooking meat…

coccyx (tail bone)

muscle that move ears

muscles that make hair stand up

little toe

wisdom teeth

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Station 4: Embryology

Evolution occurs slowly. In most cases, it is not possible to observe evolution in progress. However, evidence of evolution can be found by observing the early stages of development in vertebrates. All vertebrate embryos start out similar in appearance. This similarity has led scientists to think that these organisms have a common ancestor. The diagrams below illustrate stages in the embryonic development of a fish, a pig, and a human.

17. How does a comparison of the embryos provide evidence of evolution?

18. Which of the organisms would be most biochemically similar to humans: fish or pig?

19. Looking at the diagram below, identify the structures that each of the embryos have in common. You should do this by making a list.

20. Use evidence from your lists to explain which organism is the closest relative to man?

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21. Why do you think humans have gill-slits and tails when they are embryos? Station 5: Fossil Record

According to the geological law of superposition, older layers of sedimentary rock lay beneath younger layers. Scientists use this law to determine the order in which organisms appeared and disappeared in the fossil record. The law cannot be used to determine the absolute ages of rock layers. It can be used to determine the relative ages of rock layers by comparing their fossil records.

22. Which layer is the oldest in each formation?

a. Are the two layers the same age?

b. How could you tell?

23. Suppose fossils from layer C’ of Formation 2 are the same as fossils from layer D in Formation 1. What could you say about the age of fossils from Layer E?

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24. Suppose you also found that layers C and B’ shared similar fossils. Layers B and A’ look very similar, but contain no fossils. What could you say about the relative ages of all layers of both formations?

25. Suggest one or more geological events that might explain why Formation 2 has fewer layers than Formation 1 and describe the scenarios you chose.

This is a series of skulls and front leg fossils of organisms believed to be ancestors of the modern-day horse.

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26. Give two similarities between each of the skulls that might lead to the conclusion that these are all related species.

27. What is the biggest change in skull anatomy that occurred from the dawn horse to the modern horse?

28. What is the biggest change in leg anatomy that occurred from the dawn horse to the modern horse?

Station 6 – Molecular Evidence Cytochrome c is a protein found in mitochondria. It is used in the study of evolutionary relationships

because most animals have this protein. Cytochrome c is made of 104 amino acids joined together. Amino acid sequences of certain proteins can be used to determine how closely related different species are. If the amino acid sequences for a certain protein are very similar in two species, one can assume that those two species had a common ancestor. All 104 amino acids in the protein cytochrome c are identical in humans and chimpanzees.

Below is a list of the amino acids in part of a cytochrome protein molecule for 9 different animals. Any

sequences exactly the same for all animals have been skipped. For each non-human animal, take a highlighter and mark any amino acids that are different than the

human sequence. When you finish, record how many differences you found in the table on the next page.

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42 43 44 46 47 49 50 53 54 55 56 57 Human Q A P Y S T A K N K G I Chicken Q A E F S T D K N K G I Horse Q A P F S T D K N K G I Tuna Q A E F S T D K S K G I Frog Q A A F S T D K N K G I Shark Q A Q F S T D K S K G I Turtle Q A E F S T E K N K G I Monkey Q A P Y S T A K N K G I Rabbit Q A V F S T D K N K G I

58 60 61 62 63 64 65 66 100 101 102 103 104 Human I G E D T L M E K A T N E Chicken T G E D T L M E D A T S K Horse T K E E T L M E K A T N E Tuna V N N E T L R E K A T S - Frog T G E E T L M E S A C S K Shark T Q Q E T L R I K T A A S Turtle T G E E T L M E D A T S K Monkey T G E D T L M E K A T N E Rabbit T G E D T L M E K A T N E

Animal Number of Amino Acid Differences Compared to Human Cytochrome C

Animal Number of Amino Acid Differences Compared to Human Cytochrome C

Horse Shark

Chicken Turtle

Tuna Monkey

Frog Rabbit

29. Based on the Cytochrome C data, which organism is most closely related to humans? Explain your answer.

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30. Do any of the organisms have the same number of differences from human Cytochrome C? In situations like this, how would you decide which is more closely related to humans?

Final Review…How did you do?

Evidence Homologous

Structures Analogous Structures

Vestigial Structures

Embryological Development

Genetic Comparisons

31. A modified structure

seen among different groups of descendants

32. .In the earliest stages of development, a tail and gill slits can be seen in fish, birds, rabbits, and mammals.

33. Examples of forelimbs of bats, penguins, lizards, and monkeys

34. The forelimbs of flightless birds

35. DNA and RNA comparisons may lead to evolutionary trees

36. Bird and butterfly wings have same function but different structures.

37. A body structure reduced in function but may have been used in an ancestor