Biology Reference
In-Depth Information
CHAPTER 3
Nuclear and Extranuclear
DNA in Insects
Chapter Outline
3.1 Overview 71
3.2 Introduction 72
3.3
C-Value Paradox: Is it Real?
73
3.4
Repetitive DNA is Common in Insects
74
3.5
Composition of Insect DNA
76
3.6
Chromosomes are DNA Plus Proteins
76
3.7
Packaging Long, Thin DNA Molecules into Tiny Spaces
77
3.8
Structure of the Nucleus
79
3.9
Euchromatin and Heterochromatin
80
3.10 Centromeres 81
3.11 Telomeres 82
3.12 Chromosomes during Mitosis and Meiosis
84
3.12.1 Mitosis 84
3.12.2 Meiosis 87
3.13 Chromosome Damage
90
3.14 Polyteny 92
3.15 Chromosomal Puffing
93
3.16 B Chromosomes 94
3.17 Sex Chromosomes 94
3.18 Extranuclear Inheritance in Mitochondrial Genes 95
3.19 Transposable Elements are Ubiquitous Agents that Alter Genomes
99
References Cited
99
3.1 Overview
DNA is found in chromosomes, complex structures in the nucleus of insect
cells. Each chromosome contains a single linear DNA molecule combined with
a variety of proteins, including histones. DNA and histones form structures
called nucleosomes. Nucleosomes are arranged in a higher level of organiza-
tion that serves to condense the DNA. Chromosomes visible by light microscopy
may have discrete structures called centromeres to which spindle fibers attach
