Mutations in Chromosome Number (AQA AS Biology): Revision Note

Mutations in Chromosome Number

• Mutations can occur at different levels

• Non-disjunction occurs when chromosomes fail to separate during meiosis

  • This occurs spontaneously

• The gametes may end up with one extra copy of a particular chromosome or no copies of a particular chromosome

• These gametes will have a different number of chromosomes compared to the normal haploid number

• If the abnormal gametes take part in fertilization, then a chromosome mutation occurs as the diploid cell will have the incorrect number of chromosomes

• Chromosome mutations involve a change in the number of chromosomes

• An example of chromosome mutation is Down’s syndrome: Individuals with this syndrome have a total of 47 chromosomes in their genome as they have three copies of chromosome 21

Image showing how chromosomes failing to separate properly during meiosis can result in gametes with the incorrect number of chromosomes