Advanced Placement (AP) Biology Practice Exam

What is a centromere?

1. The point where two chromatids are joined

2. The structure forming during cytokinesis

3. A form of genetic material in prokaryotes

4. The structure that disassembles during telophase

The correct answer is: The point where two chromatids are joined

A centromere is defined as the point where two sister chromatids are joined together. This region plays a crucial role during cell division, specifically during mitosis and meiosis. The centromere ensures that chromatids are evenly divided between the two daughter cells by facilitating their proper alignment on the metaphase plate and ensuring that they are pulled apart during anaphase. The other options pertain to different cellular structures or processes. The structure forming during cytokinesis refers to the process by which the cytoplasmic division occurs, often involving a cleavage furrow or cell plate, not specifically about where chromatids are joined. As for prokaryotes, they do not have a centromere, as this term is specific to eukaryotic chromosomes which contain distinct chromosomal structures. The disassembly during telophase refers to the breakdown of the mitotic spindle and the reformation of the nuclear envelope, rather than the centromere's function. Thus, the definition of a centromere is fundamentally about its role as the connection point for chromatids, making that the correct understanding.