Cambridge O Level Biology · Syllabus 5090 · Inheritance
Chromosome Mutation
What is Chromosome Mutation?
A change in the number of chromosomes in a cell or in the structure of a chromosome. Because a single chromosome carries many genes, a chromosome mutation affects far more genetic material than a gene mutation does. The required Cambridge O Level Biology example is Down's syndrome, in which body cells contain 47 chromosomes rather than the usual 46 because there is an additional copy of chromosome 21. Chromosome mutations arise at random during the formation of gametes and are not caused by anything the organism does or needs.
This definition is part of the Inheritance chapter in Cambridge O Level Biology.
Questions students ask about Chromosome Mutation
How many chromosomes does a person with Down’s syndrome have?
47, rather than the usual 46, because there is an additional copy of chromosome 21. It is classified as a chromosome mutation because what has changed is the number of whole chromosomes, not the base sequence within a gene. It arises at random during the formation of gametes.