Read each question carefully. Write your response in the space provided for each part of each question. Answers must be written out in paragraph form. Outlines, bulleted lists, or diagrams alone are not acceptable and will not be scored. Aquaporin channel proteins are found in the plasma membrane of various cell types. Scientists studied the production of aquaporins in the keratinocytes (skin cells) of healthy individuals and found that these proteins play a role in hydration of the skin. Some individuals have a skin disorder that causes the absorption of excess water by the skin of their hands and feet when they are soaked in water. Scientists determined that the keratinocytes of these individuals are characterized by the presence of abnormal aquaporins. Scientists studied a family in which some individuals have this skin disorder and constructed a pedigree (Figure 1).

Figure 1 presents a pedigree with three generations. The first generation consists of an affected male and an unaffected female. They have the following second generation children: an affected female, an affected male, a male of unknown phenotype as indicated by a question mark, and an unaffected female. The second generation affected female has the following third generation children with an unaffected male: two unaffected males and an affected female. The second generation affected male has the following third generation children with an affected female: an affected male, an unaffected female, and an unaffected male. The second generation male of unknown phenotype has the following third generation children with an unaffected female: an affected female and an unaffected male. The second generation unaffected female has the following third generation children with an unaffected male: an unaffected male and an unaffected female.
Figure 1. Pedigree of a human family in which some members have a skin disorder. An individual with an unknown phenotype is marked by a question mark.

(a) Based on the pedigree in Figure 1, predict the most likely genotype AND phenotype of the individual marked by " ? ". Justify your prediction.

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Question 2
(b) Describe the characteristics of the keratinocyte membrane that restrict water movement across the membrane. If isolated keratinocytes are placed in a hypotonic solution for 24 hours, explain why there are likely to be far fewer cells at the end of this time than there were at the start.

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Question 3
(c) Explain how the aquaporin polypeptides are transported from the Golgi complex and inserted into the plasma membrane.

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Question 4
(d) A student claims that individuals who have a lower than normal number of aquaporins in their skin cells will easily dehydrate. Refute this claim with evidence from biological concepts.