If having a gene for Parkinson's disease guarantees that Parkinson's disease will develop, the gene is a ________.

Correct Answer: B

Rationale: The correct answer is B: necessary cause. A necessary cause is an essential factor for the disorder to occur. In this scenario, if having a gene for Parkinson's disease guarantees the development of the disease, then the gene is a necessary cause. Choice A, 'risk factor,' implies an increased likelihood of developing the disease but does not indicate certainty. Choice C, 'sufficient cause,' indicates that the gene alone can bring about the disease, which is not necessarily true in this context. Choice D, 'contributory cause,' suggests that the gene plays a part in causing the disease but is not essential for its development.

Correct Answer: B

Rationale: The correct answer is B: 'Genes play a role in most mental disorders.' This statement is true as genes do play a significant role in the development of various mental disorders. Choice A is incorrect because most behavioral disorders are influenced by a combination of genetic, environmental, and other factors, not exclusively genes. Choice C is incorrect as genes do affect biochemical processes. Choice D is incorrect because the expression of genes in an individual can be influenced by experiences and environmental factors, a concept known as gene-environment interaction.

Correct Answer: A

Rationale: Normal human cells have twenty-two chromosome pairs and one pair of sex chromosomes. This is the correct answer as it accurately describes the typical chromosome count in human cells. Choice B is incorrect because it mentions 'twenty-one trisomy chromosome pairs,' which is not characteristic of normal cells. Choice C is incorrect as it suggests having 'two trisomy chromosome pairs,' which is abnormal. Choice D is incorrect as it states 'twenty-three chromosome pairs,' which is not the standard count in normal human cells.

Correct Answer: B

Rationale: The correct answer is B because most behaviors are influenced by a complex interaction of many genes and the environment. Choice A is incorrect because it states that it is easy to differentiate between the effects of the environment and genes, which is not the case. Choice C is incorrect because although twin studies are commonly used in genetic research, this alone does not hinder the full understanding of genetic influences on behavior. Choice D is incorrect because even though we have some understanding of how genes impact brain chemistry, this does not mean that we fully understand the genetic influences on behavior.

Correct Answer: B

Rationale: The correct answer is B because most behaviors are influenced by the interaction of multiple genes and the environment. Choice A is incorrect because it suggests that researching the effects of the environment and genes is easy, which is not the case. Choice C is incorrect as it focuses on a specific method (twin studies) rather than the broader concept of gene-environment interaction. Choice D is incorrect as the statement implies a high level of understanding that contradicts the idea that genetic influences on behavior may never be fully understood.