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
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

9. Mitosis and Meiosis

Mitosis

Genetics

9. Mitosis and Meiosis

Mitosis

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2:12 minutes

Problem 27

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., 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.
Are there any possible combinations present during prophase of meiosis II other than those that you drew in Problem 26? If so, draw them.

Verified step by step guidance

Understand the context: The problem involves a diploid cell with three pairs of chromosomes (AA, BB, CC), each having a maternal (m) and paternal (p) member. The focus is on meiosis, specifically prophase of meiosis II, and whether additional chromatid combinations are possible.

Recall the key concepts: During meiosis II, the cell is haploid, and each chromosome consists of two sister chromatids. Prophase of meiosis II occurs after meiosis I, where homologous chromosomes have already separated. No further DNA replication occurs before meiosis II.

Determine the chromatid combinations: In meiosis II, the chromatids are no longer paired with their homologous counterparts (e.g., A^m is no longer paired with A^p). Instead, each chromosome consists of two sister chromatids (e.g., A^m and A^m or A^p and A^p). Consider all possible arrangements of chromatids for the AA, BB, and CC chromosomes.

Account for crossing over: If crossing over occurred during prophase I, the chromatids may now be recombinant. For example, a chromatid might contain a mix of maternal and paternal genetic material (e.g., A^m/p). This increases the number of possible chromatid combinations in prophase of meiosis II.

List all possible combinations: To determine if additional combinations are present, systematically list all potential arrangements of chromatids for each chromosome (AA, BB, CC) in the haploid cells. Include both non-recombinant and recombinant chromatids, if applicable, and compare these to the combinations identified in Problem 26.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 several stages: prophase, metaphase, anaphase, and telophase, where chromosomes are replicated and evenly distributed. Understanding mitosis is crucial for recognizing how cells replicate and maintain genetic continuity.

Meiosis

Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in four genetically diverse gametes. It consists of two rounds of division: meiosis I and meiosis II, with key processes such as crossing over and independent assortment occurring during prophase I. This concept is essential for understanding genetic variation and the formation of reproductive cells.

Chromatid Pairing and Synapsis

Chromatid pairing occurs when replicated chromosomes align closely during cell division, particularly in meiosis. Synapsis is the process during prophase I of meiosis where homologous chromosomes pair up, allowing for genetic recombination. Recognizing these processes is vital for understanding how genetic material is exchanged and how it influences genetic diversity in offspring.

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Textbook Question

Describe the 'folded-fiber' model of the mitotic chromosome.

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Textbook Question

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. Describe all that you can about these chromosomes.

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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., 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.

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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Textbook Question

During meiosis I, assuming no crossing over, what chromatid combination(s) will be present at the completion of prophase I? Draw all possible alignments of chromatids as migration begins during early anaphase.

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Textbook Question

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Explain how you determined the correct alignment of homologous chromosomes on opposite sides of the metaphase plate.

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Textbook Question

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Carefully examine and redraw these chromosomes in any valid metaphase I alignment. Draw and label the metaphase plate, and label each chromosome with its assigned letter.

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Textbook Question

Drosophila has a diploid chromosome number of 2n = 8, which includes one pair of sex chromosomes (XX in females and XY in males) and three pairs of autosomes. Consider a Drosophila male that has a copy of the A₁ allele on its X chromosome (the Y chromosome is the homolog) and is heterozygous for alleles B₁ and B₂, C₁ and C₂, and D₁ and D₂ of genes that are each on a different autosomal pair. In the diagrams requested below, indicate the alleles carried on each chromosome and sister chromatid. Assume that no crossover occurs between homologous chromosomes.

How many different metaphase I chromosome alignments are possible in this male? How many genetically different gametes can this male produce? Explain your reasoning for each answer.

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Textbook Question

For the metaphase I alignment shown in (c), what gamete genotypes are produced at the end of meiosis?

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