dizygotic dz twins share percent of their genes
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HESI Focus on Maternity Exam

1. Dizygotic (DZ) twins share _________ percent of their genes.

Correct answer: C

Rationale: Dizygotic (DZ) twins share approximately 50% of their genes. This is because dizygotic twins, also known as fraternal twins, originate from two separate fertilized eggs and share similar genetic similarity to regular siblings. Choice A (100%) is incorrect because if twins shared 100% of their genes, they would be identical twins (monozygotic). Choice B (75%) is incorrect as it is not the typical genetic similarity seen in dizygotic twins. Choice D (25%) is incorrect as it represents a significantly lower genetic similarity than what is observed in dizygotic twins.

2. _____ is a life-threatening disease, characterized by high blood pressure that may afflict women late in the second or early in the third trimester.

Correct answer: C

Rationale: Preeclampsia is a serious pregnancy complication characterized by high blood pressure that typically occurs in the second half of pregnancy. If left untreated, it can lead to severe complications for both the mother and the baby. Rubella (choice A) is a viral infection that can harm the developing fetus but is not directly related to high blood pressure in pregnancy. Syphilis (choice B) is a sexually transmitted infection that can affect pregnancy but does not specifically cause high blood pressure. Phenylketonuria (choice D) is a genetic disorder that affects metabolism and is not associated with high blood pressure in pregnancy.

3. Does the probability of having a child with Down’s syndrome increase with the age of the parents?

Correct answer: A

Rationale: The correct answer is A: TRUE. Advanced parental age, particularly maternal age, is associated with an increased risk of Down's syndrome in offspring. As parents get older, the likelihood of having a child with Down's syndrome increases. Choices B, C, and D are incorrect because the risk of Down's syndrome is known to rise with parental age, especially maternal age, due to the increased likelihood of chromosomal abnormalities during egg formation.

4. Tim, a 27-year-old man, has unusually narrow shoulders, low muscle mass, and has no facial and body hair. His doctor recently prescribed testosterone replacement therapy to him. Tim is most likely suffering from:

Correct answer: C

Rationale: Tim's physical characteristics, such as narrow shoulders, low muscle mass, and lack of facial and body hair, are typical signs of Klinefelter syndrome, a genetic condition where males have an extra X chromosome (XXY). This leads to underdeveloped testes and reduced testosterone production, resulting in features like gynecomastia, sparse facial and body hair, and reduced muscle mass. Testosterone replacement therapy is commonly used to address the hormonal imbalance in individuals with Klinefelter syndrome. Phenylketonuria (PKU) is a metabolic disorder unrelated to the symptoms described in Tim's case. Cystic fibrosis is a genetic respiratory condition that does not present with the physical characteristics mentioned. Huntington’s disease (HD) is a neurodegenerative disorder primarily affecting motor function and cognition, not physical appearance and muscle mass.

5. Most victims of _____ die of respiratory infections in their 20s.

Correct answer: B

Rationale: Individuals with cystic fibrosis have a genetic disorder that causes mucus to be thick and sticky, leading to blockages in the lungs and digestive system. This mucus buildup makes them more susceptible to severe respiratory infections, which can ultimately result in premature death in their 20s. Tay-Sachs disease (Choice A) is a genetic disorder that affects the nervous system, not typically causing respiratory infections. Turner syndrome (Choice C) and Klinefelter syndrome (Choice D) are chromosomal disorders that do not directly lead to the respiratory issues observed in cystic fibrosis.

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