In the context of Mendel's experiments, which structure in a diagram of meiosis is referred to as a tetrad?

• A. A single chromosome after DNA replication
• B. A group of four chromatids aligned during metaphase I
• C. Two homologous chromosomes separated during anaphase I
• D. A pair of sister chromatids joined at the centromere

Answer: (B)

Verified step by step guidance

1. Recall that during meiosis, homologous chromosomes pair up in a process called synapsis, which occurs in prophase I.
2. Understand that each homologous chromosome has already been replicated, so it consists of two sister chromatids.
3. When the homologous chromosomes pair, the structure formed consists of four chromatids in total (two from each homolog).
4. This group of four chromatids aligned together is called a tetrad, and it is visible during metaphase I of meiosis.
5. Therefore, the tetrad refers specifically to the paired homologous chromosomes, each made of two sister chromatids, aligned during metaphase I.