Filamentous fungi grow by the elaboration of hyphae, which may fuse to form a network as a colony develops. Fusion of hyphae can occur between genetically different individuals, provided they share a common allele at loci affecting somatic compatibility. Diversity in somatic compatibility phenotypes reduces the frequency of hyphal fusion in a population, thereby slowing the spread of deleterious genetic elements such as viruses and plasmids, which require direct cytoplasmic contact for transmission. Diverse somatic compatibility phenotypes can be generated by recombining alleles through sexual reproduction, but this mechanism may not fully account for the diversity found in nature. For example, multiple compatibility phenotypes of Fusarium circinatum were shown to be associated with the same clonal lineage, which implies they were derived by a mutation rather than recombination through sexual reproduction. Experimental tests of this hypothesis confirmed that spontaneous changes in somatic compatibility can occur at a frequency between 5 and 8 per million spores. Genomic analysis of F. circinatum strains with altered somatic compatibility revealed no consistent evidence of recombination and supported the hypothesis that a spontaneous mutation generated the observed phenotypic change. Genes known to be involved in somatic compatibility had no mutations, suggesting that mutation occurred in a gene with an as yet unexplored function in somatic compatibility.

丝状真菌通过菌丝的加工生长，随着菌落的发展，菌丝可能融合形成网络。菌丝融合可以发生在基因不同的个体之间，前提是它们在影响体细胞相容性的基因座上共享一个共同的等位基因。体细胞相容性表型的多样性降低了群体中菌丝融合的频率，从而减缓了病毒和质粒等有害遗传元件的传播，这些元件需要直接与细胞质接触才能传播。通过有性繁殖重组等位基因可以产生不同的体细胞相容性表型，但这种机制可能无法完全解释自然界中发现的多样性。例如, Fusarium circinatum 的多种相容性表型被证明与相同的克隆谱系有关，这意味着它们是通过突变而不是通过有性繁殖重组而来的。该假设的实验测试证实，体细胞相容性的自发变化可以以每百万个孢子 5 到 8 个的频率发生。具有改变的体细胞相容性的F. circinatum菌株的基因组分析显示没有一致的重组证据，并支持自发突变产生观察到的表型变化的假设。已知与体细胞相容性有关的基因没有突变，这表明突变发生在具有尚未探索的体细胞相容性功能的基因中。