Jill bears the genetic code for Von Willebrand disease, but she has never developed the illness herself. Jill would be considered:

Correct Answer: A

Rationale: Jill is a carrier of the recessive gene for Von Willebrand disease. Being a carrier means that she has one copy of the gene but does not show symptoms of the disease. Carriers can pass on the gene to their offspring. Choice B is incorrect as being a carrier does not mean she is susceptible to developing the disease after adolescence. Choice C is incorrect as 'acceptor' is not a term used in genetics in this context. Choice D is incorrect as susceptibility to the disease is not related to late adulthood in carriers of a recessive gene.

Correct Answer: C

Rationale: Tim's physical characteristics, such as narrow shoulders, low muscle mass, and lack of facial and body hair, are typical signs of Klinefelter syndrome, a genetic condition where males have an extra X chromosome (XXY). This leads to underdeveloped testes and reduced testosterone production, resulting in features like gynecomastia, sparse facial and body hair, and reduced muscle mass. Testosterone replacement therapy is commonly used to address the hormonal imbalance in individuals with Klinefelter syndrome. Phenylketonuria (PKU) is a metabolic disorder unrelated to the symptoms described in Tim's case. Cystic fibrosis is a genetic respiratory condition that does not present with the physical characteristics mentioned. Huntington's disease (HD) is a neurodegenerative disorder primarily affecting motor function and cognition, not physical appearance and muscle mass.

Correct Answer: C

Rationale: The correct answer is C. Sickle-cell anemia results from a mutation in the beta-globin gene, causing red blood cells to become sickle-shaped. These misshapen cells can obstruct small blood vessels, leading to reduced oxygen delivery to tissues. Choices A, B, and D are incorrect because sickle-cell anemia is typically managed with treatments such as pain relief medications, hydration, and in severe cases, blood transfusions. It is caused by a specific mutation in the beta-globin gene, not by the inability to metabolize phenylalanine. Additionally, sickle-cell anemia is more prevalent in individuals of African, Mediterranean, Middle Eastern, and Indian descent, not exclusive to any specific gender.

Correct Answer: B

Rationale: The correct answer is B. Cystic fibrosis is a genetic disorder that causes the body to produce thick, sticky mucus. This mucus can clog the airways in the lungs and obstruct the pancreas, leading to severe respiratory and digestive problems. Choice A is incorrect because uncontrollable muscle movements and personality changes are not typical symptoms of cystic fibrosis. Choice C is incorrect because cystic fibrosis does not directly cause red blood cells to clump together and obstruct small blood vessels. Choice D is incorrect because cystic fibrosis primarily affects the respiratory and digestive systems, not the central nervous system.

Correct Answer: A

Rationale: The correct answer is A: phenotype. A phenotype is the observable characteristics of an individual, which result from the interaction of their genotype with the environment. This interaction between genetics and the environment determines how genes are expressed and how traits are manifested in an individual. Choices B, C, and D are incorrect because chromosomes, alleles, and genotypes are components of an individual's genetic makeup, but they do not directly reflect the observable traits influenced by both genetics and the environment.