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. Align the chromosomes as they might appear at metaphase I of meiosis.
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 32b
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. Align the chromosomes as they might appear at metaphase of mitosis.

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Step 1: Understand the structure of chromatids and homologous chromosomes. Chromatids are the replicated forms of a chromosome, and homologous chromosomes are pairs of chromosomes (one from each parent) that have the same genes but may have different alleles. In this problem, you are creating models to represent these structures.
Step 2: Create the chromatids. Cut out 12 cigar-shaped structures from paper, ensuring that each set of four chromatids has the same size and shape. Label the first set of four chromatids as 'A', 'A', 'a', and 'a'. Label the second set as 'B', 'B', 'b', and 'b'. Label the third set as 'D', 'D', 'd', and 'd'.
Step 3: Form sister chromatids. For each set, cut the chromatids halfway across near their midpoint. Slide the two chromatids with the same label together at the cuts to form sister chromatids. For example, slide the two 'A' chromatids together to form one pair of sister chromatids, and do the same for the 'a', 'B', 'b', 'D', and 'd' chromatids.
Step 4: Arrange the homologous chromosomes. Place the sister chromatids of 'A' and 'a' next to each other to represent one pair of homologous chromosomes. Repeat this for the 'B' and 'b' chromatids, and the 'D' and 'd' chromatids. You now have three pairs of homologous chromosomes, for a total of six chromosomes.
Step 5: Align the chromosomes for metaphase of mitosis. Arrange the three pairs of homologous chromosomes along an imaginary metaphase plate (a central plane). Ensure that each pair is aligned such that the centromeres of the sister chromatids are in a straight line, mimicking the alignment seen during metaphase of mitosis.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chromatids
Chromatids are the two identical halves of a replicated chromosome, which are joined together at a region called the centromere. During cell division, specifically mitosis, chromatids are separated to ensure that each daughter cell receives an identical set of chromosomes. Understanding the structure and function of chromatids is crucial for grasping how genetic information is accurately distributed during cell division.
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Homologous Chromosomes
Homologous chromosomes are pairs of chromosomes that have the same structure and carry genes for the same traits, but may have different alleles. One chromosome of each pair is inherited from each parent. In the context of the question, creating models of homologous chromosomes helps visualize how genetic variation can occur during processes like meiosis, where these chromosomes can exchange genetic material.
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Metaphase of Mitosis
Metaphase is a stage in mitosis where chromosomes align at the cell's equatorial plane, preparing for separation. During this phase, spindle fibers attach to the centromeres of the chromatids, ensuring that each new cell will receive an equal and complete set of chromosomes. Understanding metaphase is essential for comprehending how cells divide and maintain genetic stability across generations.
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