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 each gamete resulting from Problem 29 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?

Verified step by step guidance

1. First, understand the chromosome setup: 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. Before mitosis or meiosis, each chromosome replicates, forming two sister chromatids per chromosome, which remain attached at the centromere.
2. For mitosis, illustrate that after replication, each chromosome consists of two identical sister chromatids (e.g., A^{m} with two identical chromatids). During mitosis, sister chromatids separate, so each daughter cell receives one chromatid from each chromosome pair, maintaining the diploid number and identical genetic content.
3. For meiosis, start by showing synapsis during prophase I, where homologous chromosomes (e.g., A^{m} and A^{p}) pair up tightly, forming tetrads of four chromatids. Crossing over may occur here, exchanging genetic material between non-sister chromatids.
4. After meiosis I, homologous chromosomes separate into two cells, each still with sister chromatids attached. Then, during meiosis II, sister chromatids separate, resulting in four haploid gametes, each containing one chromatid from each chromosome pair (either maternal or paternal origin, possibly recombinant due to crossing over).
5. For fertilization, consider that each gamete from meiosis fuses with a normal haploid gamete (with one chromatid from each chromosome). To find the combinations of zygotes, combine the chromatids from both gametes. The percentage of diploid zygotes containing one paternal and one maternal member of each chromosome pair depends on the assortment and recombination events; calculate this by considering independent assortment probabilities and crossing over outcomes.

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 doubles chromatids, preparing the cell for division, and is essential for understanding chromatid pairing during mitosis and meiosis.

Mitosis vs. Meiosis

Mitosis produces two genetically identical diploid daughter cells by separating sister chromatids, maintaining chromosome number. Meiosis involves two divisions, reducing chromosome number by half and producing haploid gametes with recombined chromatids due to synapsis and crossing over between homologous chromosomes.

Fertilization and Zygote Formation

Fertilization fuses two haploid gametes, restoring diploidy in the zygote. The genetic combination depends on the gametes' chromosome composition, including whether chromatids are maternal or paternal. Understanding this helps predict the percentage of zygotes with one maternal and one paternal chromosome from each pair.