What is the “central dogma” of genetics?

Correct Answer: C

Rationale: The central dogma of genetics states that DNA directs the production of RNA, which in turn directs the production of proteins. This process is known as gene expression. First, DNA is transcribed into RNA by RNA polymerase. Then, the RNA is translated into proteins by ribosomes. This sequence of events is crucial for the flow of genetic information within a cell. Choice A is incorrect because it reverses the sequence of events. Choice B is incorrect because RNA does not direct the production of DNA. Choice D is incorrect because while DNA is the genetic material, it does not encompass the entire central dogma of genetics.

Correct Answer: B

Rationale: Correct Answer: B Rationale: At mitosis, a chromosome looks like an "X" because after DNA replication, each chromosome consists of two identical chromatids connected at the centromere. This structure ensures that each daughter cell receives an identical copy of the genetic material during cell division, maintaining genetic consistency. The other choices are incorrect as: A: At mitosis, chromosomes condense and are not visible as double helix strands. C: "X" does not stand for a mutation; it represents the chromatids of a replicated chromosome. D: Homologous chromosomes do not form the "X" shape; it results from sister chromatids of a replicated chromosome.

Correct Answer: D

Rationale: The correct answer is D because all factors listed (A, B, and C) can influence the clinical effects of chromosome aberrations. A) Whether genetic material is lost or gained affects the function of genes. B) The amount of genetic material lost or gained can lead to more severe consequences. C) Euchromatic vs. heterochromatic material influences gene expression and function. Therefore, considering all these factors together provides a comprehensive understanding of the clinical effects of chromosome aberrations. Other choices are incorrect because they only focus on individual aspects and do not provide a holistic view.

Correct Answer: A

Rationale: Step 1: Amniocentesis and chorionic villus sampling are prenatal diagnostic tests. Step 2: These tests are performed to access fetal DNA for genetic analysis. Step 3: Amniocentesis involves extracting amniotic fluid, while chorionic villus sampling involves collecting cells from the placenta. Step 4: Both procedures allow for genetic testing of the fetus. Step 5: Choice A is correct as it accurately describes the purpose of these tests. Summary: Choices B, C, and D are incorrect because they do not accurately reflect the main purpose of amniocentesis and chorionic villus sampling, which is to access fetal DNA for genetic analysis, not to result in induced miscarriage, not just when non-invasive techniques are uninformative, and not necessarily to document a genetic defect.

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.