D2.1.9

• The base sequence of individual genes on a chromosome can change by mutation, resulting in new alleles. These alleles can be reshuffled during meiosis to produce new combinations. This is called recombination and together with gene mutation it explains how chromosomes can b homologous but not identical.
• Haploid (n) - a nucleus, cell or organism with a single set of chromosomes, which are all non-homologous
• Diploid (2n) - a nucleus, cell or organism with two sets of chromosomes and therefore homologous pairs of chromosomes
• A species has a characteristic number of types of homologous chromosomes, known as the haploid number n. Body cells in most plants and animals contain two homologous pairs of chromosomes, called diploid 2n.
• Diploid cells are produced by sexual reproduction. Gametes that fuse, are haploid so the zygote produced is diploid.
• In most organisms, normal body cells are all diploid; meiosis happens during gametogenesis.