Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A^m and A^p). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.
Are there any possible combinations present during prophase of meiosis II other than those that you drew in Problem 26? If so, draw them.

Verified step by step guidance

1. Begin by understanding the chromosome composition: the diploid cell has three pairs of chromosomes (AA, BB, CC), each with a maternal (e.g., A^{m}) and paternal (e.g., A^{p}) homolog.
2. For mitosis, first illustrate the chromosomes before replication: each chromosome is a single chromatid (A^{m}, A^{p}, B^{m}, B^{p}, C^{m}, C^{p}). Then, show replication where each chromosome duplicates into two sister chromatids joined at the centromere (e.g., A^{m} consists of two identical sister chromatids).
3. For meiosis, during prophase I, depict homologous chromosomes pairing (synapsis) to form tetrads, where each homologous pair consists of four chromatids (two sister chromatids from each homolog). Indicate this synapsis for each pair (AA, BB, CC).
4. Recall that after meiosis I, homologous chromosomes separate, and in prophase II, each cell contains chromosomes with sister chromatids but no homologous pairs. Draw the chromatids in prophase II as pairs of sister chromatids (e.g., A^{m} chromatids together), without synapsis.
5. To answer the question about possible combinations during prophase II beyond those in Problem 26, consider whether any crossing over or recombination events could create new chromatid combinations. If so, illustrate chromatids with recombinant segments paired as sister chromatids, emphasizing that no homologous synapsis occurs at this stage.

Key Concepts

Chromosome Structure and Replication

Chromosomes consist of two sister chromatids joined at a centromere after DNA replication. In a diploid cell with pairs like AA, BB, and CC, each chromosome pair has one maternal and one paternal homolog. Replication occurs during the S phase, resulting in duplicated chromatids that remain attached until separated during cell division.

Mitosis vs. Meiosis Chromatid Behavior

Mitosis involves separation of sister chromatids to produce identical diploid daughter cells, while meiosis includes two divisions: meiosis I separates homologous chromosomes, and meiosis II separates sister chromatids. Synapsis and crossing over occur only in meiosis I, affecting chromatid combinations seen in later stages.

Prophase of Meiosis II and Chromatid Combinations

During prophase II, cells have haploid sets of chromosomes, each still composed of sister chromatids. Unlike prophase I, no synapsis occurs here, so chromatid combinations reflect prior recombination events. Understanding whether new combinations arise depends on recognizing that chromatids remain paired only as sisters at this stage.