From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Separate the chromosomes as though anaphase II and telophase II have taken place.
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 32g
Textbook Question
From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts, to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Are there any alternative alignments of the chromosomes for this cell-division stage? Explain.

1
Understand the setup: You have created three pairs of homologous chromosomes, each consisting of two sister chromatids. The pairs are labeled as 'A/a,' 'B/b,' and 'D/d.' These represent homologous chromosomes, where one chromosome comes from one parent and the other from the other parent.
Recall the concept of independent assortment: During metaphase I of meiosis, homologous chromosomes align at the metaphase plate. The orientation of each pair of homologous chromosomes is independent of the others. This means that the alignment of 'A/a' does not influence the alignment of 'B/b' or 'D/d.'
Determine the possible alignments: For each homologous pair, there are two possible orientations. For example, 'A' could align on one side of the metaphase plate while 'a' aligns on the other, or vice versa. The same applies to 'B/b' and 'D/d.'
Calculate the total number of alignments: Since the orientation of each pair is independent, the total number of possible alignments is given by the formula 2^n, where n is the number of homologous pairs. In this case, n = 3 (for 'A/a,' 'B/b,' and 'D/d').
Conclude the explanation: The alternative alignments arise due to the random and independent orientation of homologous chromosomes during metaphase I. This contributes to genetic variation in the gametes produced during meiosis.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chromatids and Chromosomes
Chromatids are the two identical halves of a replicated chromosome, joined together at a region called the centromere. During cell division, specifically in mitosis and meiosis, chromatids separate to ensure that each daughter cell receives an identical set of chromosomes. Understanding the structure and function of chromatids is essential for grasping how genetic material is distributed during cell division.
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Chromatin
Homologous Chromosomes
Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci but may carry different alleles. In the context of meiosis, these chromosomes undergo processes such as crossing over and independent assortment, which contribute to genetic diversity. Recognizing the role of homologous chromosomes is crucial for understanding how genetic variation occurs during reproduction.
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Chromosome Structure
Cell Division and Alignment
During cell division, particularly in metaphase of meiosis, chromosomes align at the cell's equatorial plane before being separated into daughter cells. The orientation of homologous chromosomes can vary, leading to different combinations of alleles in the resulting gametes. This concept is vital for explaining how alternative alignments can result in genetic diversity among offspring.
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Cell-cell interactions
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