The best answer is C. The primary focus of the passage is on gene linkage; what it is and how it works. The other answer choices are too specific and do not adequately express the overall main idea of the passage.

The best answer is G. The passage states that “Each hereditary unit, the gene, contains specific ...” This clearly shows us that in this passage, a hereditary unit is referred to as a gene.

The best answer is B. The passage lists hair color, height, and susceptibility to disease all as inherited traits. Therefore, answer choice B is correct. The passage tells us that genes are found on segments of the DNA molecule,

The best answer is J. The passage describes the fruit fly as a “prolific breeder, producing hundreds of offspring in a single mating.” The word “prolific” means “productive and fertile,” which best correlates with answer choice J. This makes the most sense in the context of the passage; if fruit flies produce so many offspring in a single mating they are clearly highly productive breeders. The other answer choices do not fit the context of the sentence as well.

The best answer is C. According to the first paragraph, asexual reproduction involves a single parent.

The best answer is F. The last paragraph of the passage indicates that current research is exploring the fact that “many factors affect the transmission of certain traits from parents to offspring.” The passage goes on to state the location of genes is “but one of a multitude of determinants involved in whether or not a characteristic will be inherited.” These facts suggest that research is ongoing, and that there are still many questions regarding the transmission of genes from one generation to the next. This best correlates with answer choice F.

The best answer is B. After stating the Morgan chose to experiment on Drosophila melanogaster, the passage cites a reason for this choice: “The fruit fly is a prolific breeder, producing hundreds of offspring in a single mating.” This best corresponds with answer choice B. Although answer choice A may appear to be correct because fruit flies have easily distinguishable chromosomes, fruit flies have only four pairs of chromosomes, not “many.”

The best answer is G. As stated in paragraph 4, Morgan bred “female flies that appeared normal, but carried the mutant genes.” This tells us that the female flies held the mutant genes, yet did not appear to be mutated. This statement is best supported by answer choice G. The other answer choices are not supported by the context of the passage.

The best answer is D. The last paragraph discusses the “many factors” that affect the transmission of traits, as well as the “multitude of determinants” that determine whether a characteristic will be inherited. These statements indicate that there are many components that affect genetic transmission, which is most consistent with answer choice D. The other answer choices are not supported by the information found in the last paragraph.

The best answer is J. To answer this question, a parallel must be drawn between the logic used in the passage and the question at hand. As written in the passage “the genes for body color and wing size are transmitted together from parents to offspring because they are located on the same chromosome and must be somehow linked.” Therefore, if the genes for blue eyes and brown hair are found on the same chromosome, these two traits would be inherited together. Because the passage also states that combinations from both parents were present, it can be concluded that a certain number of offspring would inherit both blue eyes and brown hair, but a certain number of offspring would receive the eye and hair color of the other parent. This best correlates with answer choice J.