What structures are formed during prophase of meiosis I?

During prophase of meiosis I, the key event is the formation of bivalents, also known as tetrads. A bivalent consists of a pair of homologous chromosomes that have undergone synapsis, where they come together and align closely, allowing them to be recognized as a distinct unit. This process is crucial for facilitating genetic recombination through crossing over, where segments of DNA are exchanged between homologous chromosomes.

While homologous chromosomes and sister chromatids are present, they do not specifically characterize what is formed during prophase I. Each homologous chromosome is composed of two sister chromatids; however, the term "bivalent" specifically describes the paired structure that emerges as they align closely during this stage. Centromeres are structural components of chromosomes that hold sister chromatids together but do not form any new structures themselves during this phase. Therefore, recognizing bivalents as the primary structures formed is central to understanding the events that take place during prophase of meiosis I.