downs syndrome is caused by
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HESI Maternal Newborn

1. What causes Down's syndrome?

Correct answer: C

Rationale: Down's syndrome, also known as trisomy 21, is caused by the presence of an extra chromosome on the 21st pair. Choice A is incorrect as alcohol abuse is not the cause of Down's syndrome. Choice B is incorrect because Down's syndrome is not related to sex-linked chromosomal abnormalities. Choice D is also incorrect as drug abuse by the mother during pregnancy is not the cause of Down's syndrome.

2. What is the typical sex chromosome pattern for males?

Correct answer: C

Rationale: The correct answer is C: XY. In males, the typical sex chromosome pattern consists of one X chromosome and one Y chromosome. Choice A (XX) is the sex chromosome pattern for females. Choice B (XYY) is a chromosomal disorder where males have an extra Y chromosome. Choice D (XXY) is the sex chromosome pattern associated with Klinefelter syndrome, a condition where males have an extra X chromosome.

3. Humans begin life as a single cell that divides repeatedly. This cell is known as a(n):

Correct answer: A

Rationale: A zygote is the correct answer. It is the initial cell formed when a sperm cell fertilizes an egg cell, marking the beginning of human development. Choice B, gonadotrope, is incorrect as it refers to a type of hormone-secreting cell in the pituitary gland. Choice C, embryo, is incorrect as it is the stage of development after the zygote has implanted into the uterine wall and undergone initial cell divisions. Choice D, chromaffin, is incorrect as it refers to cells found in the adrenal medulla that produce and store catecholamines.

4. What is a procedure for using ultrasonic sound waves to create a picture of an embryo or fetus?

Correct answer: B

Rationale: A sonogram, also known as an ultrasound, is a procedure that utilizes sound waves to generate images of a developing embryo or fetus. This imaging technique is commonly used in prenatal care to monitor fetal development and identify any potential abnormalities. Choices A, C, and D are incorrect because a phenotype refers to an individual's observable traits resulting from genetic and environmental influences, a genotype is an individual's genetic makeup, and an alpha-fetoprotein (AFP) assay is a blood test used to screen for certain birth defects.

5. An individual’s phenotype reflects both genetic and environmental influences.

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.

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