Ch. 2 - Mitosis and Meiosis

Klug - Essentials of Genetics 10th Edition

Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook

Klug 10th Edition

Ch. 2 - Mitosis and Meiosis

Problem 21

Chapter 2, Problem 21

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

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Step 1: Define chromatin fiber by explaining that it is the complex of DNA and proteins (mainly histones) found in the nucleus during interphase, where DNA is less condensed and accessible for transcription and replication.

Step 2: Define the mitotic chromosome as the highly condensed and organized structure formed during mitosis, which ensures proper segregation of duplicated DNA into daughter cells.

Step 3: Describe the structural differences, noting that chromatin fiber is a loosely packed 10 nm or 30 nm fiber, while the mitotic chromosome is a tightly coiled and folded structure visible under a light microscope.

Step 4: Explain the relationship by stating that the mitotic chromosome is formed by further condensation and folding of the chromatin fiber, involving additional levels of packaging and scaffold proteins.

Step 5: Summarize that the chromatin fiber is the functional form of DNA during most of the cell cycle, and the mitotic chromosome is the condensed form that ensures accurate DNA distribution during cell division.

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Key Concepts

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

Chromatin Fiber Structure

Chromatin fiber is a complex of DNA and proteins, primarily histones, that forms a loosely packed structure in the nucleus during interphase. It exists mainly as a 10 nm 'beads-on-a-string' form or a more compact 30 nm fiber, allowing gene accessibility for transcription and replication.

Mitotic Chromosome Organization

Mitotic chromosomes are highly condensed and organized structures formed during cell division to ensure accurate DNA segregation. They consist of tightly coiled chromatin fibers, making them visible under a microscope and preventing DNA damage during mitosis.

Relationship Between Chromatin Fiber and Mitotic Chromosome

Mitotic chromosomes arise from the further condensation and folding of chromatin fibers. The chromatin fiber serves as the fundamental unit that compacts into the dense mitotic chromosome, linking gene regulation in interphase to chromosome segregation in mitosis.

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Related Practice

Textbook Question

If one follows 50 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed? How many first polar bodies would be formed? How many ootids would be formed? If one follows 50 primary spermatocytes in an animal through their various stages of spermatogenesis, how many secondary spermatocytes would be formed? How many spermatids would be formed?

Textbook Question

What is the probability that, in an organism with a haploid number of 10, a sperm will be formed that contains all 10 chromosomes whose centromeres were derived from maternal homologs?

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

During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. How many chromosomes are present in

(a) the mature ovum and

(b) the second polar body?

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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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