CHAPTER 8 Variation in Chromosome Structure and
Number
8.1 Microscopic Examination of Eukaryotic Chromosomes
8.2 Changes in Chromosome Structure: An Overview
8.3 Deletions and Duplications
8.4 Inversions and Translocations
8.5 Changes in Chromosome Number: An Overview
8.6 Variation in the Number of Chromosomes Within a Set: Aneuploidy
8.7 Variation in the Number of Sets of Chromosomes
8.8 Natural and Experimental Mechanisms That Produce Variation in Chromosome
Number
Allelic variation: variation in specific genes.
Genetic variation: genetic differences among members of the same species or among different
species.
, 8.1 Microscopic Examination of Eukaryotic Chromosomes
Cytogeneticists: scientists who study chromosomes microscopically. These scientists have
various ways to classify and identify chromosomes. The three most commonly used features
are location of the centromere, size, and banding patterns that are revealed when the
chromosomes are treated with stains.
Chromosomes are classified with regard to centromere location as follows:
- Metacentric: the centromere is near the middle;
- Submetacentric: the centromere is slightly off center;
- Acrocentric: the centromere is significantly off center, but not at the end;
- Telocentric: the centromere is at one end.
The short arm of the chromosome is designated with the letter p (petite).
The long arm of the chromosome is designated with the letter q.
Karyotype: a photographic representation in which all of the chromosomes within a single cell
arranged in a standard fashion (numbered big to small).
Because different chromosomes often have similar sizes and centromeric locations, geneticists
must use additional methods to accurately identify each type of chromosome within a
karyotype. For detailed identification, chromosomes are treated with stains to produce
characteristic banding patterns (e.g. G bands).
The banding pattern of eukaryotic chromosomes is useful because:
- When stained, individual chromosomes can be distinguished from each other, even if they
have similar sizes and centromere locations;
- Banding patterns are used to detect changes in chromosome structure. Chromosomal
rearrangements/changes in the total amount of genetic material are more easily detected;
- Chromosome banding is used to assess evolutionary relationships between species. The
similarity of chromosome banding patterns is a good measure of genetic relatedness.
Number
8.1 Microscopic Examination of Eukaryotic Chromosomes
8.2 Changes in Chromosome Structure: An Overview
8.3 Deletions and Duplications
8.4 Inversions and Translocations
8.5 Changes in Chromosome Number: An Overview
8.6 Variation in the Number of Chromosomes Within a Set: Aneuploidy
8.7 Variation in the Number of Sets of Chromosomes
8.8 Natural and Experimental Mechanisms That Produce Variation in Chromosome
Number
Allelic variation: variation in specific genes.
Genetic variation: genetic differences among members of the same species or among different
species.
, 8.1 Microscopic Examination of Eukaryotic Chromosomes
Cytogeneticists: scientists who study chromosomes microscopically. These scientists have
various ways to classify and identify chromosomes. The three most commonly used features
are location of the centromere, size, and banding patterns that are revealed when the
chromosomes are treated with stains.
Chromosomes are classified with regard to centromere location as follows:
- Metacentric: the centromere is near the middle;
- Submetacentric: the centromere is slightly off center;
- Acrocentric: the centromere is significantly off center, but not at the end;
- Telocentric: the centromere is at one end.
The short arm of the chromosome is designated with the letter p (petite).
The long arm of the chromosome is designated with the letter q.
Karyotype: a photographic representation in which all of the chromosomes within a single cell
arranged in a standard fashion (numbered big to small).
Because different chromosomes often have similar sizes and centromeric locations, geneticists
must use additional methods to accurately identify each type of chromosome within a
karyotype. For detailed identification, chromosomes are treated with stains to produce
characteristic banding patterns (e.g. G bands).
The banding pattern of eukaryotic chromosomes is useful because:
- When stained, individual chromosomes can be distinguished from each other, even if they
have similar sizes and centromere locations;
- Banding patterns are used to detect changes in chromosome structure. Chromosomal
rearrangements/changes in the total amount of genetic material are more easily detected;
- Chromosome banding is used to assess evolutionary relationships between species. The
similarity of chromosome banding patterns is a good measure of genetic relatedness.
