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 of each daughter cell as they might appear in metaphase II 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 32e
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. What are the genotypes of the daughter cells?

1
Step 1: Understand the concept of homologous chromosomes and sister chromatids. Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes but may carry different alleles. Sister chromatids are identical copies of a chromosome connected at the centromere.
Step 2: Recognize that the labeling of chromatids ('A' and 'a', 'B' and 'b', 'D' and 'd') represents alleles of genes on homologous chromosomes. 'A' and 'a' are alleles for one gene, 'B' and 'b' for another, and 'D' and 'd' for a third gene.
Step 3: Recall the process of meiosis, which involves the separation of homologous chromosomes during meiosis I and the separation of sister chromatids during meiosis II. This results in four daughter cells, each with half the number of chromosomes as the parent cell.
Step 4: Determine the possible combinations of alleles in the daughter cells. Since homologous chromosomes segregate independently during meiosis, each daughter cell will receive one allele from each homologous pair. For example, a daughter cell might inherit 'A', 'B', and 'D' or 'a', 'b', and 'd'.
Step 5: Conclude that the genotypes of the daughter cells depend on the random assortment of alleles during meiosis. The possible genotypes are combinations of one allele from each homologous pair, such as 'ABD', 'AbD', 'aBD', 'abD', 'ABd', 'Abd', 'aBd', and 'abd'.

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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 analyzing genetic outcomes in daughter cells.
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Homologous Chromosomes
Homologous chromosomes are pairs of chromosomes that have the same structure and gene sequence but may carry different alleles. In the context of meiosis, these chromosomes undergo processes such as crossing over, which increases genetic diversity. Recognizing homologous chromosomes is crucial for determining the genotypes of daughter cells after cell division.
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Genotype and Alleles
A genotype refers to the genetic constitution of an organism, specifically the alleles present for a given gene. Alleles are different versions of a gene that can result in variations in traits. In this experiment, the genotypes of the daughter cells will depend on the combinations of alleles from the parent chromatids, which can be predicted based on the labeling and pairing of chromatids.
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