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.
Assume that during meiosis I none of the C chromosomes disjoin at metaphase, but they separate into dyads (instead of monads) during meiosis II. How would this change the alignments that you constructed during the anaphase stages in meiosis I and II? Draw them.

Verified step by step guidance

1. Step 1: Begin by representing the original diploid cell with three pairs of chromosomes: AA, BB, and CC. Each pair consists of a maternal (e.g., A^{m}) and a paternal (e.g., A^{p}) chromosome. Before replication, each chromosome is a single chromatid.
2. Step 2: Illustrate chromosome replication during the S phase, where each chromosome duplicates to form two sister chromatids joined at the centromere. Now, each pair (e.g., A^{m}) consists of two identical sister chromatids (A^{m} and A^{m}), and similarly for A^{p}, B^{m}, B^{p}, C^{m}, and C^{p}. This results in pairs of sister chromatids for each chromosome.
3. Step 3: For meiosis I, show synapsis where homologous chromosomes pair up (e.g., A^{m} pairs with A^{p}), forming tetrads (four chromatids). This pairing occurs for all three chromosome pairs (AA, BB, CC). Indicate that crossing over may occur at this stage, but focus on the pairing structure.
4. Step 4: At anaphase I of meiosis, normally homologous chromosomes separate and move to opposite poles. However, the problem states that the C chromosomes do not disjoin at metaphase I, meaning both homologous C chromosomes move together to the same pole as dyads (pairs of sister chromatids still joined). Illustrate that AA and BB pairs separate normally, but CC pairs remain together as dyads.
5. Step 5: At anaphase II, sister chromatids usually separate into monads. However, the problem specifies that C chromosomes separate into dyads instead of monads. This means sister chromatids of C chromosomes do not separate and move together to the poles. Show that for AA and BB, sister chromatids separate normally, but for CC, sister chromatids remain paired as dyads during anaphase II.

Key Concepts

Chromosome Structure and Replication

Chromosomes consist of two sister chromatids joined at a centromere after DNA replication. In a diploid cell, each chromosome pair has one maternal and one paternal homolog. Replication duplicates each chromatid, resulting in paired sister chromatids that are identical until separated during cell division.

Mitosis and Meiosis Stages

Mitosis produces two identical diploid daughter cells by separating sister chromatids during anaphase. Meiosis involves two divisions: meiosis I separates homologous chromosomes (dyads), and meiosis II separates sister chromatids (monads). Synapsis and crossing over occur in prophase I, pairing homologs tightly.

Chromosome Disjunction and Non-disjunction

Disjunction is the normal separation of chromosomes or chromatids during anaphase. Non-disjunction occurs when chromosomes fail to separate properly, leading to abnormal chromosome numbers. In the question, C chromosomes fail to disjoin in meiosis I but separate as dyads in meiosis II, altering the expected alignment and segregation patterns.