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Summary Chapter 8 - Variation in Chromosome Structure and Number
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Chapter 8 of Genetics by Brooker.
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Chapter 8 Variation in chromosome structure and number8.1 Microscopic examination of eukaryotic chromosomes
Genetic variation refers to genetic differences among members of the same species or
among different species. Allelic variation refers to the differences in specific genes.
Cytogeneticists examine the chromosome from many members of a given species to
determine the common chromosomal composition and to identify rare individuals that show
variation in chromosome structure and/or number. They use three features to classify and
identify chromosomes: 1. Location of the centromere 2. Size 3. Banding patterns.
Location of the centromere:
- Metacentric: centromere is near the middle
- Submetacentric: centromere is slightly off the center
- Acrocentric: centromere is significantly off the center but not at the end
- Telocentric: centromere is at one end
Karyotype: micrograph in which all of the chromosomes within a single cell have been
arranged in a standard fashion.
Banding pattern:
- Individual chromosomes can be distinguished from each other
- Detect changes in chromosome structure
- Assess evolutionary relationships between species
8.2 Changes in chromosome structure: an overview
Overview:
- Deletion: a segment of chromosomal material is missing
- Deficiency: A missing region of a chromosome
- Duplication: A section of a chromosome is repeated more than once within a
chromosome
- Inversion: A change in the direction of the genetic material along a single
chromosome
- Translocation: One segment of a chromosome becomes attached to a different
chromosome or to a different part of the same chromosome.
- Simple: A single piece of chromosome is attached to another chromosome
- Reciprocal: Two different chromosomes exchange pieces, thereby altering
both of them
8.3 Deletions and duplications
The loss of genetic material in a deletion tends to be detrimental to an organism. A
chromosomal deletion occurs when a chromosome breaks in one or more places and a
fragment of the chromosome is lost.
Single break: A normal chromosome has broken into two separate pieces. The piece
without the centromere is eventually lost from future daughter cells because it usually does
not find its way into the nucleus following mitosis and is degraded in the cytosol. This event
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