The basic genetic architecture of fungi is fairly typically eukaryotic, and all the major principles of genetics apply – Mendelian segregations, recombination, chromosomal structure, gene structure, etc. (Clutterbuck, 1995a). Nevertheless, there are some differences between most fungi and most of the rest of the eukaryotes. These will be summarised here; detailed information can be obtained from Carlile and Watkinson (1994), Elliott (1994) and Chiu (1996).

Fungi have a generally smaller genome size than other eukaryotes (Clutterbuck, 1995b). The yeast, Saccharomyces cerevisiae, for example, has a haploid genome of about 15 × 106 base pairs, which is less than four times the size of the genome of the bacterium Escherichia coli (Table 5.1). Fungal nuclei are consequently difficult to study by conventional cytological procedures because both nuclei and chromosomes are small, variable in shape and indistinct by conventional microscopy. Progress in understanding nuclear changes during the fungal life cycle has been slow, though in recent years the study has benefited greatly from application of electron microscopy and molecular techniques for analysing the karyotype.

Fungal mitotic divisions are intranuclear, unlike most animals and plants, which means that their division spindle is formed within an intact nuclear membrane. This makes the progress of the division even more difficult to see and study, but does not appear to affect the biological consequences of the mitotic division.