Fungi need nutrients similar to animals and bacteria. Unlike green plants, they can synthesize food by themselves. The combination of two compatible bacterial nuclei. This nuclear combination is achieved through swimming gamete mating, gametophyte contact mating, gametophyte mating, sex spore mating and somatic cell mating. The typical sexual reproduction process includes three distinct stages: the first stage is called plasmolysis, that is, two protoplasts with nuclei cooperate with each other in the same cell; The second stage is called nuclear coordination, that is, the coordination of two nuclei in the above cells. Some fungi perform nuclear pairing immediately after a large number of pairing, and the number of chromosomes is reduced to haploid again, which is the third stage of sexual reproduction.

These spores are the dormant bodies used by many fungi to survive in adversity, and they are also the first infected bodies discovered by many plant pathogenic fungi, which is of great significance for the rejuvenation of fungi or the formation of heterosis. At the same time, sexual spores are also an important basis for fungal classification.

According to the affinity of sexual reproduction, fungi can be divided into two categories: consanguineous cooperation and heterothallism: the former is that each cell can get pregnant by itself and can have sexual reproduction alone without the help of other cells; The latter is that every cell is sterile, whether hermaphrodite or not, it needs the help of other compatible cells for sexual reproduction. Heterothallism is divided into two categories: bipolar and quadrupole. There is also parthenogenesis in fungi. In 1952, G. Pontecorvo and Roper of the United States discovered the mechanism leading to gene recombination in filamentous fungi. In this mechanism, gene recombination does not depend on meiosis of sexual reproduction, but on mitosis of quasi-sexual reproduction.

The first step of quasi-sexual reproduction is to form heterokaryon. There are three ways to form heterokaryon hyphae: ① the combination of heterokaryon hyphae; (2) Nuclear mutation of homogeneous hyphae; ③ Some haploid nuclei in hyphae are paired to form diploid nuclei. The second step of quasi-sexual reproduction is the fusion of two nuclei. Homogeneous and heterogeneous nuclei can be paired to form homodiploid nuclei and heterodiploid nuclei. Therefore, there are at least five types of nuclei in mycelium cells at this stage: two haploid nuclei, two homozygous diploid nuclei and one heterozygous diploid nucleus. However, the frequency of spontaneous formation of heterodiploid nuclei is very low, for example, Aspergillus nidulans has only one heterodiploid in 654.38+0 million strains. The third step of quasi-sexual reproduction includes a series of atypical and irregular haplotypes of diploid nuclei. Because sister chromatids are not separated in the late mitosis, or because one chromosome splits into two and tends to one pole, the number of chromosomes in the daughter nucleus is unequal, resulting in aneuploidy. There is one chromosome (2n+1) in the1subnucleus and one chromosome (2n- 1) in the second subnucleus. "2n+ 1" aneuploid, also known as trisomy, often loses one chromosome and becomes diploid. In this process, you can change from heterozygote to homozygote. "2n- 1" aneuploid, also known as haploid, often loses chromosomes in continuous mitosis until it becomes haploid. The whole process of quasi-sexual reproduction can be summarized as cytoplasmic matching, nuclear matching and haploid. Only a few species of Aspergillus, Penicillium and Fusarium have quasi-sexual reproduction.

In mitosis of heterodiploid reproduction, chromosomes are occasionally exchanged to form new combinations and chains (see linkage and exchange). Some new diploid nuclear combinations enter spores during conidia formation, and diploid hyphae are produced when spores germinate. This recombination is the main aspect of quasi-sexual reproduction, because it enables fungi without sexual reproduction to obtain the benefits of sexual reproduction. However, the frequency of occurrence is very low, and only sexual reproduction 1/500.

Although the inheritance of quasi-sexual cycle contains sexual reproduction, there are still some differences from sexual cycle: ① The process of quasi-sexual cycle is similar to sexual cycle, but it is not as fixed as sexual cycle, and a large number of aneuploids will be sacrificed to complete haploid; (2) In a hyphal cell, heterokaryons and heterokaryons can appear at the same time, but the chances of heterokaryons appearing are rare, and they can only be found by further separation. Because the frequency of spontaneous segregation of diploids (somatic hybridization and haploid) is very low, it usually needs to be induced by various chemical or physical factors. For example, p-fluorophenylalanine (PFA) has a particularly significant effect on inducing haploid of Aspergillus nidulans, and fluorouracil (FU) has an obvious effect on inducing mitotic exchange (somatic crossing over) of Aspergillus nidulans. In addition, nitrogen mustard, formaldehyde, ultraviolet and other factors can induce haploid and mitotic exchange of Aspergillus nidulans.

The discovery of quasi-sexual reproduction further deepened the understanding of fungi. Through somatic cell recombination, we can qualitatively study the genes on chromosomes in asexual fungi first, and then cross-breed in semi-ignorant fungi. In the evolution of semi-unknown bacteria, some seem to have fixed quasi-sexual reproduction, rather than sexual reproduction. Fungi (such as lichen, mycorrhiza and entomogenous fungi) coexist with other organisms and benefit from each other.