Saturday, March 23, 2019

Heterothallism in fungi




Heterothallism in fungi


·        If fungi require 2 different strains mycelium to form zygospores it is called heterothallic fungi.

Is all fungi are heterothallic


  • ·        No, there are basically 2 types of fungi.one heterothallic that needs different nature mycelium to produce zygospore.

  • ·        And  another is homothallic that do not need different nature mycelium.

  • ·        The mycelium developed from single spore are compatible for each other.

  • ·        They can make zygospores on hyphae of a single mycelium.

About heterothallic fungi

·        The 2 different mycelium are morphological similar but physiological and sexual different.
·        The term + and – for two type of strains.

History

  • ·        While studying mucorales- Blakeslee found that some species develop zygospores Independtly ,whereas some (like m.mucedo)produce zygospores in the presence of mass of mycelium.

  • ·        The 2 mycellium of mucedo arising from different spores are nessery for the production of zygospores  and also different in strains.

  • ·        These mycelium were morphological similar but not physiological and sexual.

Further,
    Work on heterothallism and homothallism by raper proved there is
                            “no absolute separation of sex”

4       type of mycellim in achlya bisexualis are found by them-
1-    Pure male
2-     predominetly male(can make oogonia)
3-    Pure female
4-    Predominantly female ( can make antherdia)
5-    But none of them able to make zygospores alone.
·        Each needs one of three .
·        These type of heterothallism called- gynandromictic.
Hormones

·        These are some chemical that govern sexual process that are called hormones.
·        Raper named them A, B, C, D.
·        One of them is sirenin that is isolated from allomyces .
·        Sirenin is responsible to attract male gametes.

Type of heterothallism

1-morphological heterothallism
2- Physiological heterothallism

Morphological heterothallism
·        When one can distinguish the male and female sex organ by its structure or morphology.

 Physiological heterothallism



  • ·        Reproduction place by physiological different hyphae.
  • ·        Also known as haploid incompatibility.
           They are two types 
               1.     2 allele
                     2.     Multiple allele
2 allele heterothallism

  • ·        Nuclei  of both mating types are genetically different.
  • ·        Sexual compatibility is controlled by genetic factor. “A” , “a”.
  • ·        Both factors are present in different chromatid of chromosomes.
  • ·        Due to dominance of “A” over “a” they also represented by “+” and “-“.
  • ·        At meoisi they got seprate with chromatid.
  • ·        Spores formed with on “+” allele and another spore formed of  “–“ allele.
  • ·        Spore with + allele give rise to + mycelium and – to – mycelium.
  • ·        Only “+” and “-“ are compatible together.


To be continue…..



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