Correct Answer: D

Rationale: Huntington's disease is a fatal genetic neurologic disorder characterized by progressive nerve cell degeneration in the brain. It typically manifests in middle age with symptoms such as involuntary movements, cognitive decline, and psychiatric disturbances. Tay-Sachs disease (Choice A) is a genetic disorder that primarily affects the nervous system in early childhood, not middle age. Duchenne muscular dystrophy (Choice B) is a genetic disorder that primarily affects muscle function and usually presents in early childhood. Hemophilia (Choice C) is a genetic disorder related to blood clotting, and its onset is not typically in middle age.

Correct Answer: D

Rationale: An amniocentesis in this scenario is most likely being performed to assess fetal lung maturity. This is necessary when considering early delivery due to macrosomia (large fetal size), which is a common concern in gestational diabetes. Evaluating fetal lung maturity is crucial to determine if the fetus's lungs are developed enough to support breathing independently outside the womb. The presence of a neural tube defect and chromosomal abnormalities are not typically assessed through amniocentesis in this situation, and determining the gender of the fetus is not the primary purpose of the procedure here.

Correct Answer: D

Rationale: A platelet count of 60,000/mm3 is significantly low and can indicate HELLP syndrome, a severe complication of preeclampsia that involves hemolysis, elevated liver enzymes, and low platelet count. HELLP syndrome requires prompt medical intervention to prevent serious maternal and fetal complications. The other findings listed are within normal limits or not directly related to the severe condition associated with HELLP syndrome.

Correct Answer: C

Rationale: Individuals with Klinefelter syndrome have an extra X chromosome (XXY) and typically have reduced testosterone levels, which can lead to gynecomastia (enlarged breasts). This condition is not usually associated with Down syndrome (choice A), XYY syndrome (choice B), or Turner syndrome (choice D), making them less likely to have gynecomastia.

Correct Answer: A

Rationale: The correct answer is A: 'They regulate the development of traits.' Genes play a crucial role in regulating the development of traits by encoding proteins that control various bodily functions and characteristics. This process involves gene expression and the production of proteins that ultimately determine an individual's traits. Choice B is incorrect because genes do not have a direct role in preventing foreign particles from entering the body; this function is primarily carried out by the immune system. Choice C is incorrect as genes do not specifically work with lutein to influence development; genes operate independently to regulate trait expression. Choice D is incorrect as genes are not responsible for transferring oxygen in the bloodstream; this function is carried out by red blood cells and hemoglobin.