downs syndrome is caused by
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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. Is a low sperm count or lack of sperm the most common infertility problem in men?

Correct answer: A

Rationale: A low sperm count or lack of sperm is indeed one of the most common causes of infertility in men. Factors such as hormonal imbalances, genetic issues, reproductive anatomy problems, and lifestyle factors can also contribute to male infertility. Choice B is incorrect because a low sperm count is a prevalent issue among men facing infertility, making it a common problem. Choices C and D are incorrect as they do not accurately reflect the prevalence of low sperm count as a cause of infertility in men.

3. Rico is a man who has enlarged breasts and suffers from mild mental retardation. He has a problem learning languages, and his body produces less of the male sex hormone testosterone than normal males. Rico is most likely suffering from:

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.

4. According to a study conducted in 2013 by Fellman, what affects the chances of having twins?

Correct answer: B

Rationale: The correct answer is B. According to the study by Fellman in 2013, the chances of having twins actually increase with parental age. Choice A is incorrect as the study does not specify a younger age for conceiving to increase the chances of twins. Choice C is incorrect as the frequency of intercourse before conception is not a highlighted factor in the study. Choice D is also incorrect as the study does not discuss the impact of fertility drugs on the likelihood of having twins.

5. What is the process in which the double helix of deoxyribonucleic acid (DNA) duplicates?

Correct answer: B

Rationale: Mitosis is the correct answer because it is the process of cell division in which a cell duplicates its DNA and divides into two identical daughter cells. During mitosis, the DNA is replicated, and each daughter cell receives an identical copy of the genetic material. Amniocentesis is a medical procedure to collect amniotic fluid for prenatal genetic testing and is not related to DNA duplication. Meiosis is a type of cell division that produces gametes with half the genetic material of the parent cell, leading to genetic diversity. Mutation is a permanent alteration in the DNA sequence that can lead to genetic variations but is not the process of DNA duplication.

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