Video Transcript
The genetic material of eukaryotic cells is found in the form of chromosomes. Which of the following best describes a chromosome? (A) A chromosome is a specialized protein that controls the division of the cell. (B) A chromosome is a threadlike structure of DNA that has been condensed and coiled. (C) A chromosome is a section of DNA that codes for a particular protein. (D) A chromosome is a short, single strand of DNA that is ready to be replicated. Or (E) a chromosome is a variant of a gene.
This question states that the genetic material of eukaryotic organisms exists in the form of chromosomes. In humans, our DNA is organized on 46 chromosomes in the nucleus of our cells. Usually, these chromosomes are all mixed up, and we really can’t differentiate one from another. So let’s remove all but two so we can see them better.
In preparation for cell division, these chromosomes replicate to make an additional copy. Then, the replicated chromosomes begin to condense and coil to create the well-known X-shaped structure. This condensation allows for the accurate and efficient separation of chromosomes during cell division. This way, the copied DNA can be separated into two cells during mitosis. In fact, the word part “mitos” in mitosis means threads, and it refers to how these chromosomes look like threads under the microscope during mitosis. Now let’s go through our answer choices to choose which one best describes a chromosome.
Answer choice (A) states a chromosome is a specialized protein that controls the division of the cell. This is incorrect because a chromosome is not a protein. It’s a structure made up of DNA. Answer choice (B) states a chromosome is a thread-like structure of DNA that has been condensed and coiled. This sounds like a good description of a chromosome. But let’s see if the other answer choices have a better description. Answer choice (C) states a chromosome is a section of DNA that codes for a particular protein. A chromosome is more than just a section of DNA. It’s made up of a long molecule of DNA. This description sounds more like a gene, so this is incorrect. Answer choice (D) states a chromosome is a short, single strand of DNA that is ready to be replicated. DNA is often double stranded, and chromosomes are made up of double-stranded DNA that is typically very long. So this is incorrect. Answer choice (E) states a chromosome is a variant of a gene. This sounds more like the definition for an allele, not a chromosome, so this is incorrect.
Therefore, the answer choice that best describes a chromosome is (B). A chromosome is a thread-like structure of DNA that has been condensed and coiled.
