In this article we will discuss about: 1. Heterothallism in Fungi 2. Heterokaryosis in Fungi 3. Parasexuality. Heterothallism in Fungi: A. F. Blakeslee, an American. heterokaryosis The presence in the same cell of two or more genetically different nuclei. Heterokaryosis occurs naturally in certain fungi, in which it results from. Heterokaryosis, the association of genetically diverse nuclei in a system capable of propagation, is a phenomenon peculiar to, but common in, the fungi. During.

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Essentially, a heterokaryon possesses two sets of chromosomes, just like a diploid heterokaryois, but instead of being contained in a single nucleus, the two sets of chromosomes lie in separate nuclei, sharing the same cytoplasm.

Every step differs drastically.

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Both the daughter nuclei are called aneuploidy. The requirement for the other thallus does not lie in morphologically distinct sex organs, but in genetically-different nuclei which are not available in the same mycelium. These can also be homo or heterothallic. When genetically divergent nuclei come together in the plasmodium form, cheaters have been shown to emerge. Fungi in this category have two jn types, each containing genetically different nuclei.

The resulting zygote must have the genotype Aa, Bb. This transient heterokaryon can produce further haploid buds, or cell nuclei can fuse and produce a diploid cell, which can then undergo mitosis.


A hermaphroditic fungus having both the sex organs may be homothallic or heterothallic. They called this parasexual cycle.

A similar alternative to sexual heterokaryosjs was discovered in the imperfect fungus, Aspergillus nidulans, in by Pontecorvo and Roper of Glasgow. Sorting Out of Diploid Strains: Blakeslee observed, that while some isolates of Mucor formed sporangia as well as zygospores e.


The diploid colonies show appearance of sectors on the Petri plate, which produce haploid conidia. This is a special type of syncytium. Here’s how it works: During mitosis of the diploid nucleus, the chromatids fail to separate non-disjunction in the anaphase stage.

This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes. However, if crossing over does not take place, only two types of spores AB and ab or Ab and aB are formed and only two types of thalli are produced. Heterothallism in Fungi 2. Heterothallism is a device for achieving outbreeding, which is a genetic desirability. On the basis of the distribution of sex organs, fungi can be put in the following categories: The cell, and the hypha or mycelium containing it, is known as a heterokaryon ; the most common type of heterokaryon is a dikaryon.

Heterokaryosis can lead to individuals that have different nuclei in different parts of their mycelium, although in ascomycetes, particularly in ” Neurospora “, nuclei have been shown to flow and mix throughout the mycelium.

Whether nuclei migrate from one thallus to another is a debated point but the hyphae having nuclei of both parents arise at the point of fusion. The dioecious fungi, in which the male and the female sex organs are borne on different thalli are, by necessity, heterothallic.

Heterokaryon – Wikipedia

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia. Both exist in a single cell at the same time and carry out different functions with distinct cytological and biochemical properties.


The haplodization occurs not by a reduction division meiosisbut by aneuploidy, a phenomenon in which chromosomes are lost during mitotic divisions. Heterokaryosis is the main source of variation in the anamorphic imperfect fungi, which lack sexual reproduction. The term heterokaryon was coined inindependently by B. Heterokaryosis is often accompanied by parasexual cycle.

heterokaryosis |

The presence of genetically-different nuclei in an individual is called heterokaryosis, and the organism heterokaryon. It happens in the following manner. Esser suggested the use of the terms monoecious and dioecious, as done in higher plants. Watkins, and by Y. Both species lack sexual reproduction. Only those thalli that have nuclei carrying opposite genes for both the factors can mate.

Then, copy and paste the text into your bibliography or works cited list. The term was first used for ciliate protozoans such as Tetrahymena. When the two sex organs, present on the same mycelium, are unable to mate, this is because of self-sterility and is called physiological heterothallism. Heterokaryosis is a major factor in natural variability and sexuality.

A heterokaryon is a multinucleate cell that heterokaryosid genetically different nuclei. This happens because the nuclei in the ‘plasmodium’ form are the products of many pairwise fusions between amoeboid haploid individuals. This can occur naturally, such as in the mycelium of fungi during sexual reproduction, or artificially as formed by the experimental fusion of two genetically different cells, as e. Heterokaryotic and heterokaryosis are derived terms.