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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Heterothallism is a device for achieving outbreeding, which is a genetic desirability. Thus four types of spores AB, Ab, aB and ab are formed which give rise to four types of thalli. This has two types of cell nuclei, a inn, somatic macronucleus and a small, germline micronucleus. The segregation of the diploid strains occurs when uninucleate diploid conidia are formed.

The spores give rise to two types of thalli, which must come together to bring together the two nuclei carrying the compatibility factors A and a.

A medical example is a heterokaryon composed of nuclei from Hurler syndrome and Hunter syndrome. The colonies that are formed hwterokaryosis diploid conidia are heterokaryoss by various methods, e.

When the two sex organs, present on the same mycelium, are fingi to mate, this is because of self-sterility and is fungj physiological heterothallism. During meiosis, the two chromosomes, containing the alleles A and a are separated in the haploid spores germ spores, ascospores, or basidiospores. This indicates that some diploid nuclei must have undergone haplodization, forming haploid nuclei, which later get sorted out in haploid conidia.


Fungi in this category have two mating types, each containing genetically different nuclei. This transient heterokaryon can produce further haploid buds, or cell nuclei can fuse and produce a diploid cell, which can then undergo mitosis. The diploid colonies show appearance of sectors on the Petri plate, which produce haploid conidia.

Both the daughter nuclei are called aneuploidy. Some of these haploids are genetically different from the original haploid parental nuclei.

Both of these diseases result in problems in mucopolysaccharide metabolism. The sexually-undifferentiated fungi e.

The heterothallic forms provide another example of physiological heterothallism. The cell, and the hypha or mycelium containing it, is known as a heterokaryon ; the most common type of heterokaryon is a dikaryon. On the basis of the distribution of sex organs, fungi can be put in the following categories: Heterokaryons show dominance and, thus, resemble diploids in many respects.

Heterokaryosis in Fungi 3. Blakeslee, an American Geneticist, in made an important observation with Mucor, which resulted in the discovery of Heterothallism. There can be four types of thalli and one thallus can mate with only one of the rest three. It happens in the following manner. 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.


Modern Language Association http: The term heterokaryon was coined inindependently by B. They called this parasexual cycle.

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Cite this article Pick a style below, and copy the text for your bibliography. 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. Diploid heterozygous heterokaryosos are formed very rarely at a frequency of one in a million. From Wikipedia, the free encyclopedia.

heterokaryosis |

The heterokaryotic condition can arise in a fungus by three methods, viz. Sorting Out of Diploid Strains: BiologyFungiHeterothallism in Fungi. Nuclear fusion in somatic heterokaryotic hyphae was first noted by Roper in Aspergillus nidulans. This situation is termed secondary homothallism. Both species lack sexual reproduction. Heterokaryosis is a major factor in natural variability and sexuality.

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