How many pairs of autosomes does a human zygote contain?

Correct Answer: D

Rationale: A human zygote contains 22 pairs of autosomes and one pair of sex chromosomes, totaling 46 chromosomes. Therefore, the correct answer is 22. Choices A, B, and C are incorrect because they do not accurately represent the number of autosomes in a human zygote. Option A (46) represents the total number of chromosomes in a human zygote, not the number of autosomes. Option B (44) is incorrect as it does not account for the correct number of autosomes. Option C (23) is inaccurate since it represents the total number of chromosomes in a human gamete, not the number of autosomes in a zygote.

Correct Answer: B

Rationale: When an individual inherits a recessive gene for eye color from both parents, the recessive trait will be expressed in the child. This is because having two copies of the recessive gene overrides the presence of any dominant gene. Choice A is incorrect because the expression of the trait is determined by the genetic makeup, not the gender of the child. Choice C is incorrect as the expression of the recessive trait is certain when both parents pass on the recessive gene, but it does not mean that all offspring will express the trait. Choice D is incorrect because if both parents provide a recessive gene, the dominant trait will not be expressed in the child, but it does not mean it will be suppressed; rather, the recessive trait will be expressed.

Correct Answer: C

Rationale: The correct answer is C. According to a study in 2013 by van Gameren-Oosterom, individuals with Down syndrome often exhibit deficits in cognitive development. This is a common characteristic of Down syndrome, along with other health challenges. Choice A is incorrect because individuals with Down syndrome are at a higher risk of cardiovascular problems, contrary to being unlikely to die from them. Choice B is incorrect as Down syndrome is associated with specific characteristic features such as distinctive facial characteristics, making the statement that they have no specific features incorrect. Choice D is incorrect as individuals with Down syndrome have an extra copy of chromosome 21, resulting in a total of 47 chromosomes, not 46.

Correct Answer: A

Rationale: Rico's symptoms align with Klinefelter syndrome, which is characterized by an extra X chromosome in males (XXY). Enlarged breasts (gynecomastia), mild mental retardation, learning difficulties, and reduced testosterone production are common features of Klinefelter syndrome. Choice B, Tay-Sachs disease, is a genetic disorder that affects the nervous system and is not associated with the symptoms described. Choice C, Turner syndrome, occurs in females with a missing or partially missing X chromosome and does not fit Rico's profile. Choice D, Down syndrome, is caused by an extra copy of chromosome 21 and typically does not present with the symptoms mentioned for Rico.

Correct Answer: C

Rationale: Sickle-cell anemia is a genetic disorder caused by inheriting two copies of a recessive gene, one from each parent. The correct answer is C. Choice A is incorrect because sickle-cell anemia is not primarily caused by a chromosomal abnormality. Choice B is incorrect as the condition is not linked to a single segment found only on the Y chromosome. Choice D is unrelated as it mentions a decrease in estrogen levels, which is not a cause of sickle-cell anemia.