“Unique” (or low copy) DNA sequences

Correct Answer: A

Rationale: Step 1: Unique DNA sequences are low copy number regions that are present in the genome in limited copies. Step 2: These sequences anneal slowly because of their low copy number, making them distinct from high copy number sequences. Step 3: Unique sequences can include functional genes as well as non-coding regions. Step 4: By combining steps 1-3, we can conclude that all of the above statements are true for unique DNA sequences, making option A correct. Summary: Option B is incorrect because the slow annealing is specific to unique sequences. Option C is incorrect as unique sequences can include non-functional regions too. Option D is incorrect because unique sequences can represent more than 1.5% of the human genome.

Correct Answer: A

Rationale: The correct answer is A because preimplantation diagnosis involves screening embryos for genetic abnormalities before they are transferred to the uterus, allowing for the exclusion of abnormal embryos. This ensures that only healthy embryos are selected for implantation, increasing the chances of a successful pregnancy. Choice B is incorrect because preimplantation diagnosis is not done for the creation of stem cells but rather to identify genetic abnormalities. Choice C is incorrect because the purpose of preimplantation diagnosis is not to make decisions about terminating pregnancies but to select healthy embryos for transfer. Choice D is incorrect because preimplantation diagnosis must be done before implantation to identify abnormal embryos and avoid transferring them.

Correct Answer: A

Rationale: Step-by-step rationale: 1. In vitro fertilization (IVF) is commonly used when a couple faces infertility issues. 2. IVF involves fertilizing an egg with sperm outside the body in a laboratory setting. 3. This method helps couples who struggle with conceiving naturally. 4. Choice A is correct as it aligns with the primary purpose of IVF for couples experiencing fertility problems. Summary: - Choice B is incorrect as preimplantation diagnosis is a separate procedure within IVF. - Choice C is incorrect as IVF is not primarily for observing early development but for assisting in conception. - Choice D is incorrect as the optimization of the fertilized egg is not the main goal of IVF, but rather achieving pregnancy for couples with fertility challenges.

Correct Answer: D

Rationale: Certainly! The correct answer is D because both ionizing and non-ionizing radiation originate from the sun (A), are part of the electromagnetic spectrum (C), and have the potential to cause cancer (B) depending on the dose and exposure. Ionizing radiation has higher energy and can directly damage DNA, leading to cancer. Non-ionizing radiation has lower energy but can still cause harm, such as skin burns or increasing cancer risk with prolonged exposure. Therefore, all of the above choices are correct as they accurately describe characteristics of both types of radiation.

Correct Answer: B

Rationale: The correct answer is B (50%). This is because empirical data shows that around half of Americans live in areas with poor air quality due to factors like pollution, industrial activities, and traffic congestion. Choice A (10%) is too low and underestimates the prevalence of poor air quality in the US. Choice C (75%) is too high and exaggerates the problem, as not three-quarters of Americans are affected. Choice D (90%) is also an overestimation, as the majority but not almost all Americans are impacted by poor air quality. Therefore, B is the most accurate representation of the proportion of Americans living in areas with poor air quality.