Chapter 9-02 - Pearson Homework PDF

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Chapter 9-02 Due: 11:59pm on Tuesday, November 30, 2021 You will receive no credit for items you complete after the assignment is due. Grading Policy

HHMI Video: The Biology of Skin Color Click on the image below to launch the video in a new tab and then answer the questions.

Part A Which of the following statements apply to the variation in human skin color? Select all that apply. ANSWER:

Human skin color variation evolved recently in hominid evolution, once some populations of our human ancestors migrated out of Africa. Variability in human skin color can be explained by the activity of a single gene. Human skin color variation is primarily determined by the type and amount of melanin pigment in the skin. The color of human skin and the skin of our closest primate relative exhibits a similar range in variability. Human skin color variation likely evolved in response to differences in the intensity of sunlight around the world.

Correct Evidence suggests that human skin color variation, which is determined by the amount and type of melanin in the skin, evolved in response to varying intensities of UV radiation in different parts of the world.

Part B Which of the following statements accurately describes melanin's function? ANSWER:

Lighter skin has less of the dark-brown eumelanin that protects cells from UV damage. Melanin is a molecule that distinguishes humans from their primate relatives. The more melanin an individual has in his or her skin cells, the more likely he or she is to get mutations in DNA. Everyone has the same type of melanin, but the amount varies from person to person.

Correct People with darker skin have more eumelanin. People with lighter skin tones produce mostly the reddish-yellow pigment pheomelanin.

Part C Darker skin is more prevalent in high-UV areas. Dr. Nina Jablonski proposed a hypothesis to explain the selective pressure for darker skin in these environments. On what evidence did she base this hypothesis? ANSWER:

the melanin in darkly pigmented skin protects DNA from UV radiation, and UV radiation can cause skin cancer she discovered that people of African descent have less folate circulating in their blood and that folate is important for human reproduction people of African descent all have the same version of the MC1R gene, indicating that this gene was under selection the melanin in darkly pigmented skin protects circulating folate from being destroyed by UV radiation, and folate is important in human reproduction

Correct This observation led Dr. Jablonski to propose that being able to protect folate from destruction by UV radiation would provide a selective advantage to individuals living in a high-UV environment.

Part D Human populations in low-UV environments tend to have more lightly pigmented skin. One explanation is that the selective pressure for dark skin decreases as UV intensity decreases. At the same time there is selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production. What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones? ANSWER:

red hair and light skin are typical of people of northern European descent indigenous peoples living at high latitudes have darker skin, but they eat foods rich in vitamin D lightly pigmented people tend to be at higher risk of vitamin D deficiency lightly pigmented people cannot synthesize vitamin D in high-UV environments, such as equatorial Africa

Correct Populations that get ample vitamin D from their diets may therefore have had relaxed selection for lighter skin. This observation supports the idea that the need for vitamin D production provided the selective pressure for the evolution of lighter skin.

Part E Based on the risk factors discussed in the video, which of the following groups would be most likely to develop the bone disease rickets? ANSWER:

adults with dark skin who live close to the equator children born to parents with dark skin living far from the equator adults with light skin who live far from the equator children born to parents with light skin living close to the equator

Correct Children born to parents with dark skin would likely have dark skin. Dark skin coupled with low UV intensity during winter months can limit vitamin D synthesis in the skin and lead to vitamin D deficiencies. In children, vitamin D deficiency can cause rickets.

Part F In what way does natural selection depend on the specific environment in which an organism lives? ANSWER:

natural selection produces traits that are always either helpful or harmful, regardless of the environment. when the environment changes, traits that were beneficial to an organism may become harmful and vice versa. natural selection is random, and the direction of the selective pressure cannot be predicted based on the environment. when an organism enters a new environment, it evolves all of the traits it needs to survive there

Correct The evolution of a trait is often a balance of conflicting selective pressures that are influenced by the environment.

Learning through Art: Codominant Cross Can you correctly label the genotypes and phenotypes in this Punnett square of a cross that traces human blood types?

Part A Human ABO blood type is determined by a single gene that comes in 3 distinct alleles: IA , IB , and i. The IA and IB alleles are each dominant to the i allele, but are codominant with each other, meaning that both phenotypes are expressed in the heterozygote. The Punnett square below shows a cross between two parents with different blood types. Drag the genotypes and phenotypes from the left to correctly complete the Punnett square. ANSWER: Reset

Type AB

Type A

Type B

Type O

Help

Correct

Learning through Art: Sex-linked Cross Can you correctly label the phenotypes in this Punnett square of a sex-linked cross?

Part A The disease hemophilia is caused by a single gene that is located on the X chromosome. Because human females have two X chromosomes (XX), they have two copies of this gene. Since hemophilia is recessive (h), a female must have two copies of the recessive allele to have the disease. A human male (XY), on the other hand, has only one X chromosome, and so needs only one copy of the recessive allele to have the disease.

Complete the Punnett square below of a cross between a carrier mother (a female who carries one copy of the recessive allele and so appears normal herself) and a non-hemophiliac father. 1. Drag the pink labels to the pink targets to indicate the sex dictated by the genotype in each box. (Pink labels may be used more than once.) 2. Drag the blue labels to the blue targets to indicate whether the genotype in each box confers hemophilia, normal, or carrier status. (Blue labels may be used more than once.) ANSWER: Reset

male female

female

male

normal

normal

female

male

carrier

hemophiliac

hemophiliac carrier normal

Correct

Everyday Biology: Cystic Fibrosis and the Promise of Gene Therapy Watch the Everyday Biology video, read the accompanying essay, and then answer the questions below.

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Because she has cystic fibrosis, Sophie must work harder than most people to stay healthy. Cystic fibrosis is caused by a genetic mutation that prevents the correct functioning of the chloride carriers in the cell membranes of the cells found in mucus membranes. As a result, the mucus produced by these membranes is very thick, creating problems in places like the lungs, the gastrointestinal tract, and the pancreas. Thick mucus in the lungs clogs up the bronchioles and the alveoli, and traps bacteria that cause infections. Thick mucus in the GI tract prevents the proper absorption of food. And thick mucus in the pancreas can interfere with the production and release of insulin, leading to diabetes. Treatment involves a combination of exercise and percussive vibrations to the torso to help loosen and expel the mucus, enzymes to help break down the mucus, and antibiotics to combat infections. But over time, the permanent damage, especially to the lungs, makes long-term health and survival difficult. How did Sophie get cystic fibrosis? She was born with a mutation in the CFTR gene on chromosome 7 that codes for the building of the chloride carrier protein. We all have two copies of this gene – one from our mother, and one from our father. If you have only one bad copy of the gene, then the good copy of the gene makes enough normal proteins for you to be healthy. Since a normal gene can mask the effects of a bad gene, we consider cystic fibrosis to be a recessive genetic disease. Since Sophie has cystic fibrosis, we can infer that she has two bad copies, and must have inherited a bad gene from each of her parents. This means that both of her parents were carriers of the bad gene – they each had one bad copy, had no sign of the disease, and unfortunately they both passed that bad gene along to their daughter. How promising is gene therapy in the treatment of cystic fibrosis? There are several obstacles to overcome. In the description of the gene therapy procedure that Rhys Evens received, it sounds pretty straightforward: cells were taken from his bone marrow, mixed with copies of the healthy gene, then the cells were injected back into his body to repopulate his bone marrow. However, there are steps that must occur in that process that can impact the success of the treatment. First of all, when the cells are taken from the bone marrow and mixed with fragments of DNA containing the correct gene, there is no guarantee that those cells will indeed take up the fragments of DNA and incorporate that new DNA into the chromosomes. There is also no guarantee that cells that do incorporate the new DNA will start making proteins based on the instructions from that new DNA. And once the cells are injected back into the body, there is no guarantee that the cells will survive and take up residence in the bone marrow, and begin improving the patient’s immune system. Despite all the difficulties, gene therapy shows great promise, especially when there is a clear target for inserting the correct gene. In Rhys’ case, he just needed a few cells with the correct gene to become established in his bone marrow. But in Sophie’s case, with cystic fibrosis, she needs the correct gene inserted into ALL of the cells in ALL of her mucus membranes in order to be completely cured of the disease. Since the worst problems in a cystic fibrosis patient are with his or her lungs, the cells of the lungs are the main target for the gene therapy described in the video. But as stated in the video, the large surface area of the lungs, combined with the immune system protecting the lungs from foreign particles, make gene therapy for cystic fibrosis a challenge. Hopefully an effective method of gene therapy can be found quickly for Sophie, and for the 70,000 other people in the world with cystic fibrosis.

Part A Which of the following is LEAST likely to be a health problem for someone with cystic fibrosis? ANSWER:

obesity frequent infections nutritional deficiencies diabetes

Correct

Part B The allele that causes cystic fibrosis is recessive. An individual who is heterozygous for cystic fibrosis ANSWER:

cannot have children with cystic fibrosis. cannot reproduce. will have children who are all carriers of cystic fibrosis. is a carrier.

Correct

Part C If Sophie conceives a child, and the father neither has cystic fibrosis nor is a carrier, what are the chances that the child would have cystic fibrosis? ANSWER:

25%, because only one in four gametes will carry the bad gene 0%, because the child must receive the bad gene from both parents 75%, because Sophie has the condition but the father does not 50%, because there is a 50% chance that Sophie will pass along the bad gene 100%, because Sophie has the condition

Correct

Part D If Sophie has a brother or sister from the same parents, what are the chances that sibling would have cystic fibrosis? ANSWER:

100% 0% 75% 25% 50%

Correct

Part E If someone is a carrier of a recessive genetic disorder, it means he or she has __________ of the allele, and __________ exhibit symptoms of the disorder. ANSWER:

two copies; does one copy; does not one copy; does two copies; does not zero copies; does not

Correct

Part F Which of the following do you think contributed the most to the success of Rhys’ gene therapy? ANSWER:

Rhys was very young at the time of the gene therapy procedure. Rhys’ illness was never severe or life-threatening. Doctors were replacing only one gene, and they only had to insert that gene into bone marrow cells. Doctors were able to supplement his gene therapy with numerous rounds of bone marrow transplants.

Correct

Part G Theoretically, which of the following diseases should be the easiest to treat through gene therapy, considering the targeted organs and tissues where the corrected gene must be delivered? ANSWER:

Gaucher’s disease, where fat deposits accumulate in cells throughout the body cystic fibrosis, since the target cells are found in both the lungs and the GI tract diabetes, since the target cells are found only in the pancreas Down syndrome, since there is an extra copy of chromosome 21 in every cell of the body

Correct

Video Tutor Session Quiz: Sex-Linked Pedigrees Watch the Video Tutor Session to your right. You can also download the video or view the text of the tutor session to read while you are watching. After you have watched the tutor session, answer the questions. Estimated time: 15 minutes

Part A

ANSWER:

XhY0 XHYH XHY0 XHYh we cannot say for sure

Correct Since hemophilia is sex-linked, I must have only one copy of the gene, on my X chromosome. And since I don’t have the recessive disorder, I must have the dominant form of the gene.

Part B

ANSWER:

XbXb XBXB XBXb XBY it could be X B X B or X B X b

Correct We know that my mother passed on a dominant allele to me, so she must have an X B . But whether she has one or two copies of the X B , we cannot say for sure from the information shown here.

Part C

ANSWER:

0% 25% 50% 100% the answer cannot be determined from the information given

Correct If a woman is bald, she must have two copies of the recessive gene, so she must pass one on to her children. Since her son would get his Y chromosome from his father and his X chromosome from his mother, he would inherit her baldness gene. That means that all of her sons will be bald.

Part D

ANSWER: XBXb XbXb XBXB it could be X B X B or X b X b we cannot say for sure

Correct Since the mother has an affected son who inherited his X from her, she must have an X b to pass on to him. But she has another son who inherited an X from her but is not affected, so she must also have an X B to pass on.

Part E

ANSWER: XbXb XBXB XBXb it could be X B X B or X B X b we cannot say for sure

Correct Since she is not affected, she must have at least one X B , which she inherited from her father. But her mother is heterozygous, so we cannot say for certain whether she is a carrier or not.

Identifying Major Themes – Chapter 9

Part A Can you identify the major theme illustrated by each of the following examples? If necessary, you may review the themes in Chapter 1 of your book. Match the themes on the left with the examples on the right. Not all themes will be used. ANSWER:

Reset

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The clogging of blood vessels causes a cascade of symptoms; blood flow to body parts is reduced, resulting in periodic fever, severe pain, and damage to the heart, brain, and kidneys. The abnormal cells are destroyed by the body, causing anemia and general weakness. Pathways that transform Interactions within biological systems

energy and matter

Mendel crossed homozygous plants having round-yellow seeds with plants having wrinkled-green seeds. The union of gametes from the parental generation yielded hybrids heterozygous for both characters. All of these offspring had round-yellow seeds. Information flow

Over thousands of years, genetic tinkering has led to the incredible variety of body types and behaviors we have today, from huge, docile Great Danes to tiny, spunky Chihuahuas. Evolution The H allele specifies a cell-surface receptor protein that liver cells use to mop up excess "bad cholesterol" from the blood. Each receptor protein type only accepts specific molecule shapes. With only half as many receptors on their liver cell membranes as HH individuals, heterozygotes can remove much less excess cholesterol. Relationship of structure to function

Correct Themes can help you organize and evaluate new information.

Score Summary: Your score on this assignment is 96.3%. You received 7.7 out of a possible total of 8 points....