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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1:01 minutes

Problem 22

Textbook Question

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

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Understand that the 'folded-fiber' model is a concept used to describe the structure of chromosomes during mitosis.

Recognize that this model suggests that chromatin fibers, which are composed of DNA and proteins, fold into a highly compact structure to form the mitotic chromosome.

Note that the model proposes that the chromatin fiber is approximately 30 nm in diameter and folds into loops, which are further organized into a higher-order structure.

Consider that these loops are thought to be anchored to a scaffold or matrix, providing the structural framework necessary for the chromosome to condense during mitosis.

Acknowledge that the 'folded-fiber' model helps explain how long DNA molecules can be efficiently packed into the small volume of a mitotic chromosome, ensuring proper segregation during cell division.

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Key Concepts

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

Mitotic Chromosome Structure

The mitotic chromosome is a highly condensed form of chromatin that becomes visible during cell division. It consists of two sister chromatids joined at a region called the centromere. This structure is essential for the accurate segregation of genetic material into daughter cells during mitosis.

Folded-Fiber Model

The folded-fiber model proposes that chromosomes are composed of a long DNA molecule that is organized into a series of loops or folds. These loops are further compacted and organized by proteins, allowing the chromosome to fit within the confines of the cell nucleus while maintaining the ability to be accessed for gene expression and replication.

Chromatin and Its Levels of Organization

Chromatin is the complex of DNA and proteins found in the nucleus, existing in two forms: euchromatin (less condensed, active in transcription) and heterochromatin (more condensed, generally inactive). The organization of chromatin into higher-order structures, such as the folded-fiber model, is crucial for regulating gene expression and ensuring proper chromosome behavior during cell division.

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Describe the role of the following structures or proteins in cell division:

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Describe the role of the following structures or proteins in cell division:

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Textbook Question

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?

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Textbook Question

Contrast the chromatin fiber with the mitotic chromosome. How are the two structures related?

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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

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

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