For Problems 25–30, 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. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text. 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?

Key Concepts

Mitosis

Mitosis is the process of cell division that results in two genetically identical daughter cells, each with the same number of chromosomes as the original cell. It involves a series of stages: prophase, metaphase, anaphase, and telophase, where chromosomes are replicated and evenly distributed. Understanding mitosis is crucial for recognizing how diploid cells maintain their chromosome number during cell division.

Meiosis

Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in four haploid gametes. It consists of two rounds of division: meiosis I, where homologous chromosomes are separated, and meiosis II, where sister chromatids are separated. This process is essential for sexual reproduction, as it ensures genetic diversity through recombination and independent assortment.

Chromatid Pairing and Fertilization

Chromatid pairing occurs during the S phase of the cell cycle when DNA is replicated, resulting in sister chromatids that are joined at the centromere. In the context of fertilization, when two haploid gametes fuse, they form a diploid zygote containing one maternal and one paternal chromosome from each pair. This combination is vital for understanding genetic variation and the inheritance of traits in offspring.