Human and Ape DNA Lab

Part I When you hear the word evolution, what do you think of first? For many people, the first thing that comes to mind is the phrase, “Humans evolved from apes.” However, we did not evolve directly from modern apes. Instead, we evolved from a common ancestor with modern apes. This activity will give you the opportunity to observe differences and similarities in human and ape DNA.

Background Knowledge DNA is a double helix shape DNA is made of nitrogen bases that make up the “steps of the ladder” A and T, C and G always match up and are called “base pairs”

Background Knowledge One side of DNA is called the parent strand and the opposite side is called the complimentary strand For example: A G G C A T Parent strand T C C G T A Complimentary strand

Background knowledge Organisms that share matching bases are closely related in evolution. The more bases you match, the closer you are related. Sections that do not match show differences A G T G A T C C G C A T Parent strand of Human T C C G T A Complimentary strand of Organism X Don’t Match 4 unmatched bases and 2 unmatched sections

procedure 1. Diagrams called morphologic trees, are based on comparisons of organisms. Look at the morphologic tree in figure 1 and find the part of the tree that shows the relationships between gorillas, chimpanzees, and humans. You will notice that there are no lines showing relationships. 2. Develop three hypotheses to explain how these organisms are related. On the DNA Lab Answer Sheet, under Part I, make a diagram of your hypotheses by drawing lines from point A to each of the three organisms (G = gorilla, C = chimpanzee, H = human, A = common ancestor). 3. Circle ONE of the hypotheses as the one that you think best shows the relationship between humans, gorillas and chimpanzees.

example G C H A You can use this one on your paper but make sure to make up 2 more that are from your brain

Part II Modern research techniques allow biologists to compare the DNA that codes for certain proteins and to make predictions about how closely related the organisms are based on their DNA. You will use models of these techniques to test your hypotheses.

procedures 1. Using your DNA Lab Answer Sheet, “recreate” three strands of DNA. Use the provided DNA sequences and a color code like the one listed below: blue = adenine (A) green = guanine (G) yellow = thymine (T) red = cytosine (C) 2. Recreate the three DNA strands by filling in the correct color, coded for each base in the proper sequence of DNA given for each organism. The DNA strands for all three organisms represent a section of the gene that codes for the hemoglobin protein. Hemoglobin carries oxygen in red blood cells.

procedures 3. The Human DNA strand (below) represents the parent strand. Remember DNA exists as two stands, a parent strand and a complimentary strand. Human DNA strand: (position 1) A-G-G-C-A-T-A-A-A-C-C-A-A-C-C-G-A-T-T-A (position 20) A G G C A T Now you can finish the rest…

Procedures 4. The Chimpanzee and Gorilla cDNA strands (below) represent the complimentary strand that matches to the parent strand. Chimpanzee cDNA strand: (position 1) T-C-C-G-G-G-G-A-A-G-G-T-T-G-G-C- T-A-A-T (position 20) Gorilla cDNA strand: (position 1) T-C-C-G-G-G-G-A-A-G-G-T-T-G-G-T- C-C-G-G (position 20)

procedures 5. Compare the human DNA to the chimpanzee cDNA by matching the strands base by base. Remember, the DNA bases are complementary – adenine (A) will always pair with thymine (T), and guanine (G) will always pair with cytosine (C). 6. Count the number of bases that are NOT complementary (matches) and the number of sections of bases that are NOT complementary (matches). Record your data in table 1 on your Lab Answer Sheet, under Part II. Repeat steps 5 and 6 with the human DNA and the gorilla cDNA.

Part III Biologists have determined that some mutations in DNA occur at a regular rate. They can use this rate as a “molecular clock” to predict when two organisms began to separate from a common ancestor. Most evolutionary biologists agree that humans, gorillas, and chimpanzees shared a common ancestor at one point in their evolutionary history. They disagree, however, on the specific relationships between these three species. In this part of the activity, you will use data from Table 1 to answer discussion questions and determine which hypothesis from Part I is best supported by the analyzed DNA evidence. Answer these discussion questions on the back of your Lab Answer Sheet under Part III.