Advanced Placement (AP) Biology Practice Exam

What are identical copies of a chromosome known as?

1. Homologous chromosomes

2. Sister chromatids

3. Karyotypes

4. Autosomes

The correct answer is: Sister chromatids

Identical copies of a chromosome are referred to as sister chromatids. When a cell undergoes DNA replication, each chromosome is duplicated, resulting in two identical copies linked together at a region known as the centromere. These sister chromatids are crucial during cell division, particularly in mitosis and meiosis, as they ensure that each daughter cell receives an exact copy of the genetic material. Homologous chromosomes are not identical copies; instead, they are a pair of chromosomes (one from each parent) that contain similar but not identical genetic information. Karyotypes are visual representations of an individual's complete set of chromosomes, organized by size, shape, and number, but they do not refer to the copies of chromosomes themselves. Autosomes are a specific type of chromosome that are not involved in determining sex; they can be homologous but do not describe identical copies. Therefore, sister chromatids is the precise term for identical copies of a chromosome.