Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- Chapter 1 Life Forms and Their Origins
- Chapter 2 Nucleic Acids
- Chapter 3 Proteins
- Chapter 4 Simple Chromosomes
- Chapter 5 Chromosomes of Eukarya
- Chapter 6 Genome Content
- Chapter 7 RNA Synthesis 1: Transcription
- Chapter 8 RNA Synthesis 2: Processing
- Chapter 9 Abundance of RNAs in Bacteria
- Chapter 10 Abundance of RNAs in Eukarya
- Chapter 11 Protein Synthesis
- Chapter 12 DNA Replication
- Chapter 13 Chromosome Replication
- Chapter 14 Molecular Events of Recombination
- Chapter 15 Micromutations
- Chapter 16 Repair of Altered DNA
- Chapter 17 Reproduction of Bacteria
- Chapter 18 Horizontal Gene Transfer in Bacteria
- Chapter 19 Cell Cycles of Eukarya
- Chapter 20 Meiosis
- Chapter 21 Chromosomal Abnormalities
- Chapter 22 Life Cycles of Eukarya
- Chapter 23 Reproduction of Viruses
- Chapter 24 Genetic Processes in Development
- Chapter 25 Sex Determination and Dosage Compensation
- Chapter 26 Cancer
- Chapter 27 Cutting, Sorting, and Copying DNA
- Chapter 28 Genotyping by DNA Analysis
- Chapter 29 Genetically Engineered Organisms
- Chapter 30 Genomics
- Chapter 31 Behavior of Genes and Alleles
- Chapter 32 Probability and Statistics Toolkit
- Chapter 33 Genes, Environment, and Interactions
- Chapter 34 Locating Genes
- Chapter 35 Finding and Detecting Mutations
- Chapter 36 Cytoplasmic Inheritance
- Chapter 37 Genetic Variation in Populations
- Chapter 38 Mutation, Migration, and Genetic Drift
- Chapter 39 Natural Selection
- Chapter 40 Quantitative Genetics
- Chapter 41 Speciation
- Chapter 42 Molecular Evolution and Phylogeny
- Glossary
- Index
Chapter 4 - Simple Chromosomes
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Acknowledgments
- Chapter 1 Life Forms and Their Origins
- Chapter 2 Nucleic Acids
- Chapter 3 Proteins
- Chapter 4 Simple Chromosomes
- Chapter 5 Chromosomes of Eukarya
- Chapter 6 Genome Content
- Chapter 7 RNA Synthesis 1: Transcription
- Chapter 8 RNA Synthesis 2: Processing
- Chapter 9 Abundance of RNAs in Bacteria
- Chapter 10 Abundance of RNAs in Eukarya
- Chapter 11 Protein Synthesis
- Chapter 12 DNA Replication
- Chapter 13 Chromosome Replication
- Chapter 14 Molecular Events of Recombination
- Chapter 15 Micromutations
- Chapter 16 Repair of Altered DNA
- Chapter 17 Reproduction of Bacteria
- Chapter 18 Horizontal Gene Transfer in Bacteria
- Chapter 19 Cell Cycles of Eukarya
- Chapter 20 Meiosis
- Chapter 21 Chromosomal Abnormalities
- Chapter 22 Life Cycles of Eukarya
- Chapter 23 Reproduction of Viruses
- Chapter 24 Genetic Processes in Development
- Chapter 25 Sex Determination and Dosage Compensation
- Chapter 26 Cancer
- Chapter 27 Cutting, Sorting, and Copying DNA
- Chapter 28 Genotyping by DNA Analysis
- Chapter 29 Genetically Engineered Organisms
- Chapter 30 Genomics
- Chapter 31 Behavior of Genes and Alleles
- Chapter 32 Probability and Statistics Toolkit
- Chapter 33 Genes, Environment, and Interactions
- Chapter 34 Locating Genes
- Chapter 35 Finding and Detecting Mutations
- Chapter 36 Cytoplasmic Inheritance
- Chapter 37 Genetic Variation in Populations
- Chapter 38 Mutation, Migration, and Genetic Drift
- Chapter 39 Natural Selection
- Chapter 40 Quantitative Genetics
- Chapter 41 Speciation
- Chapter 42 Molecular Evolution and Phylogeny
- Glossary
- Index
Summary
Overview
Every life form's genetic material is packaged in one or more chromosomes. Its genome is the nucleic acid in one complete set of chromosomes, excluding nonessential ones. This chapter is about the composition, size, shape, and number of chromosomes in bacteria, archaea, mitochondria, chloroplasts, and viruses – all but the eukarya. The nucleic acid of chromosomes is double stranded DNA, except for a few single-stranded DNA plasmids and except for some viruses.
Bacteria and Archaea
Bacteria and archaea have two kinds of chromosomes, essential chromosomes, which are required for the survival and normal functioning of the cell, and plasmids, which are not absolutely necessary for survival and reproduction. Most bacteria and archaea whose genomes have been analyzed have only one essential chromosome, and in nondividing (nonreproducing) cells there is one copy of that chromosome. The number of different types of plasmids per cell varies from zero to several, and the number of copies of each plasmid ranges from 1 to ~102, depending on the plasmid. Usually, essential chromosome is simply referred to as chromosome.
In most bacteria the genome is located in an amorphous region, the nucleoid (Figure 4.1), which takes up from a quarter to half the cell's volume. It is not known whether plasmids are also restricted to the nucleoid. The parts of the chromosome where DNA replication begins and ends are attached to the cell's membrane. Unlike the nucleus of a eukaryal cell, a membrane does not bound the nucleoid region.
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- Fundamental Genetics , pp. 26 - 33Publisher: Cambridge University PressPrint publication year: 2004