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This diagram shows a chromosome pair before, during and after the cross-over of genetic material that occurs during production of eggs and sperm. The diagram shows three stages. In the first stage, a label reads 'pair of homologous chromosomes' – to tell them apart, one chromosome is coloured in red, the other is coloured in blue. Stage two, labelled 'breakage occurs during meiosis' shows the same chromosomes, both of which now have a white line crossing them two thirds of the way down, indicating natural breakages. This leads to the third stage which is labelled 'rejoining to the other member of the pair', and shows that the chromosomes have exchanged genetic material at the natural breakage points, such that novel combinations are formed (i.e. both are now a mix of red and blue material).

 5.2 Genes and chromosomes