Advanced Placement (AP) Biology Practice Exam

Which best describes a chromosome?

1. A complex of proteins without DNA

2. A structure that separates during anaphase

3. A threadlike structure containing a DNA molecule

4. A cytoplasmic division entity

The correct answer is: A threadlike structure containing a DNA molecule

A chromosome is best described as a threadlike structure containing a DNA molecule. Chromosomes are made up of tightly coiled DNA and proteins, specifically histones, which help in organizing and packaging the DNA into a compact form that fits within the nucleus of eukaryotic cells. Each chromosome consists of a DNA molecule that carries genetic information crucial for the growth, development, and functioning of an organism. During the process of cell division, chromosomes become visible under a microscope as distinct structures, but their primary function revolves around the storage and transmission of genetic material. They ensure that DNA is accurately replicated and distributed during cell division, which is central to the maintenance of genetic integrity across generations. While there are other components involved in cell division, and chromosomes do undergo separation during anaphase, this action alone does not fully encapsulate the essence of what a chromosome is. Similarly, while chromosomes play a role in processes related to cytoplasmic division, especially during the latter stages of cell division, the term 'cytoplasmic division entity' does not accurately define the structure or its function in genetics.