The Biology of Skin Color: A Case Study in Human Evolution and Natural Selection

Worksheet 19 The Biology of Skin Color 1. True / False. Biologists classify specific forms of traits as good or bad. For example, long tails in cats could be classified as good and short tails as bad. false 2. Explain the reasoning or evidence you used to answer Question 1. Some organisms have an advantage with some trait s, but they have a disadvantage in other situations. 3. If you travel north from the equator, what generally happens to the intensity of ultraviolet (UV) light? _____ a. The intensity increases. b. The intensity decreases. c. The intensity stays the same. d. It is impossible to predict. 4. Who would you expect to be most at risk for developing the bone disease rickets? _____ a. Children born to mothers with dark skin, living far from the equator b. Adults with dark skin who live close to the equator c. Children born to mothers with light skin, living close to the equator d. Adults with light skin who live close to the equator e. Anyone who eats a diet that includes a lot of fish 5. Explain the reasoning or evidence you used to answer Question 4. They would not be able to make enough vitamin. 6. When Dr. Nina Jablonski describes her discovery of the UV data collected by NASA, a headline is visible that reads, “Ozone Depletion Raising Risk of Skin Cancer, Scientist Says.” Use this headline and your understanding of what causes skin cancer to infer a beneficial feature of the ozone layer for humans. Why would a depleted ozone layer increase the risk of skin cancer? Depleted ozone layer would cause a n overexposure of sunlight and skin receive more UV light than our bodies need and would cause skin cancer. 7. Ultraviolet light can cause mutations and other damage within cells, which can hurt an individual’s chance of surviving and leaving offspring. Some molecules can protect cells from damage by UV. The amount of these molecules is determined by genes. Within a population, some individuals make more of these UV-protection molecules than others. What do you predict would happen to the frequency of the genes that cause more of the molecules to be made in a population over time? Assume all other factors are equal. ______ a. The frequency would increase because individuals need the genes. b. The frequency would increase because individuals with the genes for more molecules would leave more offspring. c. The frequency would decrease because molecules are types of chemicals and having more chemicals in the body is harmful. d. The frequency would stay the same because populations do not change over time. 8. Write down the evidence or reasoning you used to answer Question 7. They would decrea se if a person lived closer to the poles and incr ease if the y were closer to the equator. 9. Describe your ideas about why indigenous groups of people in different parts of the world have different skin colors from other groups of people. In high-UV environments, darker skin offers protection from the damaging effects of UV radiation, especially to DNA and the valuable nutrient folate. 10. Describe at least three different types of evidence that support your ideas for Question 9. The effect of UV on DNA or folate, the protective effect of melanin data from anthropology documen ting the skin colors of indigenous people. Use the following scenario to answer Questions 11 and 12. A biologist was studying two indigenous groups of people from different areas of the world. The first population was from equatorial Africa. The second population was from northern Europe. The biologist was studying a gene that affects skin color. The biologist examined the gene in 100 people from each population. She kept track of how many different forms (or alleles) of the gene she found in each population. The results are in the graph in Figure 1. Figure 1. 11. Describe the major pattern in the data in Figure 1. The graph shows the number of alleles in a gene that control skin color in two different population. Population 1 from equatorial Africa shows three different alleles and population 2 from northern Europe has 16 different alleles for skin color. So, people in northern Europe has higher number of alleles in their genes that control skin color. 12. Make a claim about the strength of stabilizing natural selection on this gene in the two populations. Use evidence from the graph (Figure 1) to support your claim. People that live near the equator have a small amount of variation in skin color which helps them survive and people who live farther away from the equator have more variation which helps them live in the variations in climate and altitude. 13. Describe how having dark skin may have provided an advantage in survival and reproduction to people thousands of years ago in some places in the world but not in others. Having dark skin would give the advantage of having a smaller chance of vitamin D deficiency and would lower the chance of being unable to reproduce, because they would be outside for longer periods of time in be exposed to a lot of UV light. 14. Biologists sometimes say that “natural selection depends on the specific environment where a species lives.” What does this statement mean? _______ a. If populations of a species are in different environments, traits that individuals need to meet their needs in each environment will appear. b. Traits can be helpful or harmful. If populations of a species are in different environments, some traits that are helpful in one environment might be harmful in another environment. c. Traits are always either helpful or harmful, and the environment of a population doesn’t matter. If populations of a species are in different environments, the same traits will always be helpful. d. Species were formed to perfectly match their environment. The traits of individuals in a species depend on the specific environment in which they were created. 15. Describe how UV light is harmful to people but can also be necessary. UV light is needed for Vitamin Dproduction, but it can cause mutations in skin cells and cause skin cancer . 16. How does the synthesis of melanin by melanocytes help these cells with their major function in skin? It helps them protect the nucleus by creating a shield around it . 17. The graph in Figure 2 summarizes the age at which people are diagnosed with melanoma, the most serious form of skin cancer. Use the graph to explain why protection from skin cancer may not explain the strong selective pressure for dark skin in high-UV areas. Figure 2. A scientist proposed that skin cancer was a selective force for the evolution of dark pigmentation . Melanoma of skin is most frequently diagnosed among people aged 55-64 with median age at diagnosis being 63. Most of the melanoma patients are well past their reproductive age group. So, protection from skin cancer may not explain the strong selective pressure for dark skin in high UV light areas. Many people get skin cancer at an older age after they have already had children and probably passed the gene onto them. WS-Skin color, BIOS 208, Dr. Bergan-Roller, Fall 2020