The nuclear DNA content of a single sperm cell in Drosophila melanogaster is approximately 0.18 picogram. What would be the expected nuclear DNA content of a primary spermatocyte in Drosophila? What would be the expected nuclear DNA content of a somatic cell (non-sex cell) in the G1 phase? What would be the expected nuclear DNA content of a somatic cell at metaphase?
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
9. Mitosis and Meiosis
Mitosis
Problem 25
Textbook Question
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., Am and Ap). 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.
In mitosis, what chromatid combination(s) will be present during metaphase? What combination(s) will be present at each pole at the completion of anaphase?

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Step 1: Understand the problem. The question asks about the chromatid combinations during metaphase and at the poles after anaphase in mitosis. Mitosis is a process of cell division that results in two genetically identical daughter cells, maintaining the diploid chromosome number.
Step 2: Recall the key events of mitosis. During metaphase, replicated chromosomes (each consisting of two sister chromatids) align at the metaphase plate. Each chromosome has a maternal and paternal origin, and the chromatids are held together by a centromere. For the given cell, the chromosomes are AA, BB, and CC, with maternal (A^m, B^m, C^m) and paternal (A^p, B^p, C^p) chromatids.
Step 3: Represent the chromatid combinations during metaphase. At this stage, each chromosome is replicated, so you will have pairs of sister chromatids: A^m-A^m, A^p-A^p, B^m-B^m, B^p-B^p, C^m-C^m, and C^p-C^p. These chromatids are aligned at the metaphase plate, with spindle fibers attached to the centromeres.
Step 4: Analyze the chromatid combinations at the poles after anaphase. During anaphase, the sister chromatids are separated as the centromeres divide. Each chromatid is pulled to opposite poles of the cell. At the completion of anaphase, each pole will have one copy of each chromatid: A^m, A^p, B^m, B^p, C^m, and C^p. This ensures that each daughter cell will have a complete set of chromosomes.
Step 5: Summarize the results. During metaphase, the chromatids are paired as sister chromatids (e.g., A^m-A^m, A^p-A^p, etc.) and aligned at the metaphase plate. At the completion of anaphase, each pole will have one copy of each chromatid (e.g., A^m, A^p, B^m, B^p, C^m, C^p), ensuring the diploid chromosome number is maintained in the daughter cells.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mitosis
Mitosis is a type of cell division that results in two genetically identical daughter cells, each with the same number of chromosomes as the original cell. It consists of several phases: prophase, metaphase, anaphase, and telophase. During metaphase, chromosomes align at the cell's equatorial plane, and during anaphase, sister chromatids are pulled apart to opposite poles. Understanding these phases is crucial for analyzing chromatid combinations during these stages.
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Mitosis Steps
Chromatid
A chromatid is one half of a duplicated chromosome, which is formed during the S phase of the cell cycle. Each chromosome consists of two sister chromatids joined at a region called the centromere. During mitosis, these chromatids are separated and distributed to daughter cells. Recognizing the role of chromatids in cell division is essential for understanding the chromatid combinations present during metaphase and anaphase.
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Chromatin
Diploid Cell
A diploid cell contains two complete sets of chromosomes, one from each parent, denoted as 2n. In the context of the question, the diploid cell has three pairs of chromosomes (AA, BB, CC), which means it has six total chromosomes. This genetic configuration is important for understanding how chromosomes and chromatids behave during mitosis, particularly in terms of their alignment and separation during the different phases of cell division.
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Diploid Genetics
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