Introduction,In some fungi ,true sexual cycle comprising of nuclear fusion and meiosis is absent. These fungi derive the benefits of sexuality through a cycle know as parasexuaL cycle. First Reported by- Gudio Pontecorvo and J.A.Roper(1952) Parasexual cycle was reported in Aspergillus nidulans,the imperfect stage of Emericella nidulans. Since then parasexual cycle has been discovered not only in several members of Deutromycetes but also in fungi belonging to Ascomycetes and Basidiomycetes. DEFINETION - Parasexuality is defined as a cycle in which Plasmogamy, Karyogamy and Meiosis [Haploidization] take place in sequence but not at a specified time or at specified points in the life cycle of an organism. Generally parasexual cycle occurs in those fungi in which true sexual cycle does not take place. Parasexualcycle also know as Somatic recombination. PASEXUALITY ALSO REPORTED IN SOME  ORGANISMS- Aspergillus nigar, Penicillium crysogenum, STEPS OF PARASEXUAL CYCLE - 1) ESTABLISHMENT OF HETEROKARYOSIS, 2) Formation of Heterozygous DIPLOIDS, 3)  occasional mitotic crossing-over during multiplication of diploid nuclei, 4)occasional haplodization through aneuploidy , COMPARISION BETWEEN SEXUAL AND PARASEXUAL CYCLE, IMPORTANCE OF PARASEXUALITY, C0NCLUSION

1. Rashmi yadav
M.Sc. – 4th
semester

2. INTRODUCTION
In some fungi ,true sexual cycle comprising
of nuclear fusion and meiosis is absent.
These fungi derive the benefits of sexuality
through a cycle know as parasexuaL
cycle.

3. First Studied at-Department of Genetics,
University of Glasgow
GUIDO PONTECORVO

4.  Parasexual cycle was reported in
Aspergillus nidulans,the imperfect stage of
Emericella nidulans.
 Since then parasexual cycle has been discovered
not only in several members of Deutromycetes
but also in fungi belonging to Ascomycetes and
Basidiomycetes.
 So,far it has not been rported in Phycomycetes
fungi.

5.  Parasexuality is defined as a cycle in which
Plasmogamy, Karyogamy and Meiosis
[Haploidization] take place in sequence but not at a
specified time or at specified points in the life cycle of
an organism.
 Generally parasexual cycle occurs in those fungi in
which true sexual cycle does not take place.
 Parasexualcycle also know as Somatic recombination.
DEFINETION

6. PASEXUALITY ALSO REPORTED IN
SOME
ORGANISMS
• Aspergillus niger
• Aspergillus
fumigatus
• Aspergillus oryzae
• Aspergillus sojae
Pontecarvo et al
[1952]
Stromnaes and
Garber [1963]
Ishitani [1956]
Ishitani et al
[1957]
ORGANISM
S

7. Penicillium
chrysogenum
Penicillium
expansum
Penicillium italicum
Ustilago maydis
Ustilago violacea
Pontecarvo and
sermonti [1957]
Barron [1962]
Stromanes et al
[1964]
Holliday [1961]
Day and Jones(1968)

8. • Ustilago hordei
• Piricularia oryzae
• Verticillium albo-
atrum
• Fusarium
oxysporum
I. Fusarium sps pisi
II.Fusarium sps cubense
III.Fusarium sps callistephi
• Dinoor and Person
[1969]
• Yamasaki and
niizeki [1965]
• Hastie [1962]
I. Buxton [1956]
II.Buxton [1962]
III.Hoffman [1967]

9. Aspergillus nigar

10. Penicillium crysogenum
penicillium crysogenum on citrus fruit

11. • The various steps of the parasexual cycle has
been worked out in detail for Aspergillus
nidulans ,Aspergillus nigar and Penicilium
chrysogenum .
• In A . nidulans which serves as the typical
example, the parasexual cycle occurs in the
following four steps;
STEPS OF PARASEXUAL
CYCLE

13. • The presence of haploid nuclei of dissimilar genotypes
in the same cytoplasm is a pre-requisite for
recombination.
• This is achieved by heterokaryosis which is bought
about by-
I. Mutation
II. Anastomosis
Between hyphae of different origin.
 This step is equal to plasmogamy of sexual
reproduction.
ESTABLISHMENT OF HETEROKARYOSIS

15. FORMATION OF HETEROzYgOUS
DIPLOIDS
• Nuclear fusion in
heterokaryotic
vegitative cells was
first noted by Roper
(1952) in A.nidulans.

16. The nuclear fusion between dissimilar nuclei
result in formation of heterozygous diploid
nuclei or zygotes a rare event, occuring at the
rate of one in a million.
• Fusion between identical nuclei to occur.
• But since the homozygous diploid nuclei thus
formed ultimatly give rise to non –
recombinant haploid nuclei

17. Such fusion have no genetic
relevence.
The heterozygous nuclei, which
are fairly stable, by multiplication
and staring out through conidia
give rise to diploid thalli.
The diploid colonies are
recognized by-

19. DNA content of A. nidulans
DNA Content
Counts

20. • When measured the DNA content of haploid
and diploid spore suspension of the
A.nidulans and A.fumigatus.
• As result of their lower amount of total DNA
per cell.
• This work demonstrates that the use of flow
cytometry is a very rapid, simple and accurate
method.

21. • To distinguish diploid and haploid spores in
Aspergillus species ,this technique could be
also applied to parasexual analysis in other
filamentous fungi, especially in those species
of industrial interest where sexual crosses are
unavailable,
(i.e-Penicillum chrysogenum, A.niger,
A.oryzae, etc).

22. • This is typical of parasexual phenomenon ,and
obviously the prolonged diploid phase, involving
repeated nuclear division enhance the chances
of mitotic crossing-over.

23. • This is the most important or key event in
parasexual cycle.
• It is during this step that genetic
recombination take place,
• Crossing over during mitosis is rare
phenomenon, first noticed in Fruit Fly by stern
in 1936.
occasional mitotic crossing-over
during multiplication of diploid
nuclei

24. • In A. nidulans mitotic crossing-over occurs
rarely, with a frequency of 10-2 per nuclear
divison.
• Intrestingly enough, in some fungi , like
Penicillium chrysogenum and Aspergillus
niger,it is as frequent as during meosis.
• Pontecorvo and roper (1952) invoked mitotic
crossing-over to explain the development of new
heterozygous, recombinant haploid nuclei,
which has subsequently also proved
cytologically.

25. • Reciprocal exchanges between homologous
chromosome at the four-strand stage were
observed by Pritchard & Roper (1995) and
Kafer (1961).
• It is charectristic feature of mitotic crossing-
over that the exchange or chiasmata
formation, is confined a single chromosome
pair out of the whole complement of
chromosomes.

26. • In meiosis, the crossing-over n all the occurs
simultaneously in all the chromosomes.
• The subsequent a splitting of chromosomes and
segregation of strands is as it occurs in mitosis .
• Crossing-over followed by segregation of strands
gives homozygosis for all markers
distal to the point of chiasma. Markers
proximal to the point of exchange and markers
on other chromosomes remain heterozygous.

27. • The haploid nuclei give rise to haploid nuclei by
gradual loss of chromosomes during succesive
mitotic divisions .This is called Haplodization .
Meiosis is not involved .
• The haplodization , which occurs at a constant
frequency of 10-3 per nuclear division ,is the
result of Aneuploidy .
occasional haplodization
through aneuploidy

28. During mitotic division , non-disjunction of the
chromatic of one chromosomes pair result in aneuoloid
nuclei which can be represented as (2n-n) i.e haploid
at the end .
The aneuploids are genetically unstable , and ones the
loss of chromosomes has started , the selection favours
the development of fully balance haploid nuclei .
Parasexual cycle closely stimulates the events of th
sexual cycle .
It involves everthings , Plasmogamy ,Karyogamy an
Haplodization , but in modified form and without an
fixed plan with regard to time and space .

29. • Parasexual cycle closely stimulates the events of
the sexual cycle .
• It involves everthings , Plasmogamy
,Karyogamy and Haplodization , but in
modified form and without any fixed plan with
regard to time and space .
• The two processes nevertheless , end with
similar results , i.e give rise to recombinant
haploid nuclei.

31. 1) Nuclear fusion is in
speciallized
structures .
2) Zygote usually
persist one nuclear
generation only .
1) Rare nuclear fusion
in vegitative
structures cells .
1) Zygote persist
through many
mitosis .
SEXUAL CYCLE
PARASEXUAL
CYCLE

32. 3) Recombination by
meiosis crossing-over
in all chromosome
pair, reduction of
chromosome number,
random assortment of
members of each
chromosome pair.
3) Recombination by rare
accidants of mitosis ,
a. Mitotic crossing-over
,at each event usually
confined to one
exchange in singal
chromosome arm.

33. 4) Products of meiosis
readily recognised and
isolated .
b) Haplodization
independent of
crossing-over ,random
assortment of members
of each chromosome
pair.
4) Recombinanant occur
among vegitative cells ,
recognised only by use
of suitable genetic
markers .

34. • Some of the most important antibiotic producing
fungi, like Penicillium chrysogenum
(penicillin) and Acremonium chrysogenum
(cephalosporin), lack sexual reproduction. The
discovery of parasexual phenomenon in them
has provided suitable techniques to obtain
higher antibiotic strains. Some antibiotic
producing fungi in which parasexual genetic
recombination have been established are the
following:

35. • Aspergillus nidulans
• Acremonium chrysogenum
• Emericellopsis
salmosynnemata
• Penicillium chrysogenum
• Penicillium patulum.
• Penicillin G
• Ephalosporin C
• Penicillin N
• Penicillin G,O,V
• Griseofulvin patulin
FUNGI ANTIBIOTIC

36. • Parasexuality has been known only a laboratry
phenomemon.
• However the result of Ingram(1968) strongly
suggested that it may be widespread in nature.

37. • Through it has been demonstrated only
Ascomycotina,Basidiomycotina and
Deuteromycotina ,there are strong
evidences of its occurrence in some
coenocytic fungi like Phytopthora
cactorum .
• The phenomenon is linked with
heterokaryotic condition ,

38. Which is very frequently encountered in
nature populations.
But every heterokaryotic species may not
necessarity be parasexual.
Thus “The role of parasexuality in the
origin of individuals to be assessed.

39. Introduction to Mycology by- H.C. Dube Third
edition .
An introduction to Mycology – R S Mehrotra . K R
Aneja .
Introduction of Mycology by -Alexopoulos ,Mins
and Blackwell .
Parasexual cycle –Wikipedia the free encyclopedia .