Sex and sexuality are very common words in biology but para-sexuality is a little bit uncommon, several organisms in general and fungi in particular have the pleasure of sexuality to bring variations by beside sex. This PPT explores the beauty of para-sexuality for the academic fraternity.

1. MYCOLOGY-
PARASEXUALITY IN FUNGI
A Presentation by:
Dr. N. Sannigrahi,
Associate Professor,
Department of
Botany,
Nistarini College,
Purulia
D.B. Road, Purulia
(W.B) India

2. CONTENTS
 What is Parasexuality ?
 Occurrence of Parasexuality,
 Steps of Parasexuality
 i. Establishment of heterokaryosis,
 ii. Formation of heterozygous diploids or diplodization,
 iii. Occasional mitotic crossing over,
 iv. Haplodization
 V. Sorting of new haploid strains
 Comparison between sexual cycle & Parasexual cycle,
 Significance of Parasexuality

3. PARASEXUALITY ?
 Sexual reproduction needs two sex organs along with two non-identical
gametes followed by nuclear fusion . In Fungi, zygotic meiosis takers place
for the formation of haploid gametophyte,
 In some cases in fungi, a different way to describe the benefits of sexual
cycle,
 The sexuality by the aforesaid process is treated as parasexuality and the
cycle of occurrence is called parasexual cycle. Here, ‘Para’ means ‘beside’
Sex.
 First reported by Gudio Pontecarvo and J.A. Roper ( 1952) on the basis of
the study of imperfect stage of Aspergillus nidulans.
 In normal events, plasmogamy, karyogamy & meiosis take place in
sequence but in parasexual cycle, the events somewhat take place but not in
proper order or specified time,
 It is also called somatic recombination because in this case, genetic
material exchange take place during mitosis without the pleasure of the
development of desired sex organs.

4. OCCURENCE
 This pleasure of sexual occurrence of exception behavior is found in many
fungi since this discovery in Aspergillus nidulans,
 Mostly found in the class of Deuteromycetes or Fungi Imperfecti or
Synthetic Fungi as no normal sexual reproduction does not take place,
 Some members of Basidiomycets , Ascomycetes in certain cases,
 Some notable fungi have the occurrence like Aspergillus fumigates, A.
oryzae, Penicillium chrysogenum, P. expansum, P. indicum, Ustilago
vioacea, U. horedei, Piricularia oryzae, Verticillum alboratum, Fusarium
oxysporum etc.
 This event is not ordinary one , rather it is the exceptional one as far as
sexual behavior is concerned.

5. PARASEXUAL PROCESS

6. STEPS OF PARASEXUAL CYCLE
 According to Pointecarvo ( 1958), parasexual cycle in A. nidulans, the
following steps are involved in parasexual cycle.
 i. Formation of heterokaryotic mycelium- Either by Mutation or
Anastomosis or Diplodisation,
 ii. Fusion between two nuclei- Fusion between like nuclei & fusion
between unlike nuclei,
 iii. Multiplication of diploid nuclei,
 iv. Occasional mitotic crossing over,
 v. Sorting out of diploid nuclei,
 vi. Occasional Haplodization of diploid nuclei,
 vii. Sorting of new haploid strains

7. MECHANISMS
 Establishment of heterokaryosis -
 Heterokaryosis means the occurrence of nuclei of dissimilar genotypes in
the same cell or cytoplasm,
 The presence of dissimilar two haploid (n) nuclei in the same cytoplasm is
the preliminary requirement for genetic recombination,
 In these fungi, this heterokaryotic condition is achieved either by
anastomosis or sometimes by mutation,
 Whatever may be, the heterokaryon is established prior to the pleasure of
beauty of this episode.
 Formation of Heterozygous diploid or diplodization-
 The nuclear fusion in heterokaryotic vegetative hyphae or cells was first
reported by Roper, 1952.
 Here, the nuclear fusion between dissimilar nuclei results in the formation
of heterozygous diploid nuclei

8. MECHANISMS
 The heterozygous nuclei that are fairly stable , by multiplication and
starting out through conidia give rise to diploid thalli,
 The diploid colonies are characterized by higher DNA content , bigger size
conidia and phenotypic characters of the colony,
 Fusion between identical nuclei is found, the homozygous diploid nucleus
formed due to this ultimately give rise to non-recombinant haploid nuclei,
such forms have no genetic relevance,
 In this heterokaryon, a mixture of the two original haploid nuclear types as
well as diploid fusion nuclei are formed.
 Occasional Mitotic Crossing Over:
 Very key event in the parasexual cycle,
 In this stage, genetic recombination take place,
 Crossing over during mitosis is a rare phenomenon as first reported in the
fruit fly by Stern (1936),
 In Aspergillus nidulans, the mitotic crossing over occurs but with a
frequency of 10-2 per nuclear division

9. MECHANISMS
 Reciprocal exchanges between homologous chromosomes at the four-
stranded stage were reported by Pitcher and Roper. It is the characteristic
feature of mitotic crossing over that exchange or the chiasmata formation is
confined to a single chromosome pair out of the whole complement of
chromosomes.
 Haplodization:
 It is the formation of haploid nuclei from the diploid nucleus due to non-
disjunction of chromosomes occurring during division of the diplod
nucleus,
 It is also very exceptional feature,
 The formation of haploid nucleus does not undergo meiosis. During mitotic
division of the diploid (even the haploid cell) irregularity (non-disjunction)
during chromosomes separation leads to some nuclei with 2n-1 and some
with 2n+1, thereby, exhibiting aneuplody either hypoploidy or hyperploids,
 Such aneuplody nuclei with incomplete multiplies of haploid number tend
to be unstable, further chromosomes during subsequent mitotic divisions
until 2n-1 & 2n+1 progressively revert to n state.

10. MECHANISMS
 Sorting of new haploid (n) strains:
 Some diploid (2n) nuclei undergoes Haplodization in the mycelium and are
sorted out by incorporation of haploid nuclei in the uninucleate conidia.
Some of these haploid strains are genotypically different from the parent
because of mitotic recombination.
 Thus, the parasexual cycle has operated for sometime , the mycelia may
contain the following types of nuclei:
 Haploid nuclei like those of both parents,
 Haploid nuclei with various new genetic recombination,
 Several types of diploid homozygous nuclei,
 Several types of diploid heterozygous nuclei.
The parasexual cycle closely stimulates the events of sexual cycle .It
involves every components of the sexual cycle like plasmogamy,
karyogamy, Haplodization but little bit of modified form and without any
fixed plan with regard to time and space. But the two processes both the
sexual and parasexual cycle give rise to the recombinant of haploid nuclei.

11. COMPARISON BETWEEN SEXUALITY & PARASEXUALITY
Sr.
No.
Sexual cycle Parasexual Cycle
1. Nuclear fusion takes place in the
specialized structure.
Nuclear fusion takes place rarely in
vegetative cells.
2. Zygote usually persists one nuclear
generation.
Zygote persists through many
mitosis.
3. Recombination by meiosis, crossing
over in all chromosomes pair, of
reduction of chromosome number and
random assortment of numbers of each
chromosome pair are characteristics of
the cycle.
Recombination by rare accidents of
mitosis; mitotic crossing over at
event usually confined to one
exchange in a single chromosome
arm and Haplodization independent
of crossing over are the features of
this cycle.
4. Products of meiosis can easily be
recognized and isolated.
Products can be recognized by the
application of suitable genetic
markers.

12. SIGNIFICANCE OF PARASEXUALITY
a. It is very important in industrial processes,
b. Several fungi having high degree of industrial application belong to Fungi
Imperfecti and these fungi operate parasexual cycle.
c. New and better strains of fungi are obtained by mutation through
parasexual cycle,
d. The strains of desirable characters can be developed through mitotic
recombination,
e. It can be also applied in the analysis of genetic and physiological
processes of perfect and imperfect fungi,
f. Parasexual cycle has also been successfully employed in the genetic
control of pathogenecity and host-range in several species of Fusarium.

13. PARASEXUALITY- THE BEAUTY OF SEX LIFE IN FUNGI
References:
 Google for images
 Introduction to Mycology & Phytopathology - Mishra & Dash
 Brook Microbiology of Microorganisms-Madigan, Martinko, Bender,
Buckley & Stahl,
 Botany for degree students; Fungi- Vashishta & Sinha,
 A Textbook of Microbiology- Chakraborty,
 Microbiology- Pelzer, Chan & Krieg,
 Different WebPages to enrich content.
Disclaimer: This PPT has been designed to enrich the open source of learning.
The author does not claim any kind of financial pleasure.

14. THE SEXUAL BEHAVIOR AND ITS SCIENTIFIC BEAUTY IS
A PLEASURE TO BIOLOGISTS.
THANKS A LOT TO VISIT THIS CONTENT