This document discusses different types of sexual reproduction in fungi. It describes homothallism, where a single mycelium is self-fertile, and heterothallism, where two different mating types are required. There are two types of homothallism: primary, where spores contain a single genotype, and secondary, where spores contain nuclei of compatible mating types. Heterothallism can involve morphological or physiological differences between mating types, and be controlled by multiple alleles at one or two unlinked loci. Experiments by Blakeslee demonstrated that zygospores in Mucor hiemalis only form between two different fungal strains, proving the existence of heterothallism.

1. HOMOTHALLISM
AND
HETEROTHALLISM
PREPARED BY-
AMARNATH UPADHYAY
CLASS ROLL NO. : 21
PAPER : MIBCC(102)

2. CONTENTS
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INTRODUCTION
HOMOTHALLISM
TYPES OF HOMOTHALLISM
HETEROTHALLISM
TYPES OF HETEROTHALLISM
REFERENCES

3. INTRODUCTION
The fungal kingdom have evolved paradigmatic sexual systems which includes
outbreeding systems with up to thousands of mating types at one end of the spectrum
and self-fertile, inbreeding systems at the other. There are three central dichotomies to
consider regarding sex in fungi : (a) inbreeding/ selfing (homothallism) versus
outbreeding (heterothallism) modes of reproduction; (b) the sex determinants encoded
by the mating-type (MAT) locus; (c)sex systems with a single biallelic locus (bipolar)
versus systems with two unlinked, multi allelic sex loci (Tetrapolar).
Sexual reproduction is central to eukaryotic evolution via its ability to increase genetic
diversity and eliminate deleterious mutations. These mode of sexual reproduction share
key features (e.g., ploidy changes, meiosis, etc.) but differ in other key features involving
aspects of cell or hyphal fusion.

4. HOMOTHALLISM
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Homothallism is the phenomenon in those fungi which are self-fertile and self-compatible. Such fungi
are known as Homothallic fungi.
The thallus in these fungi is of one and single strain, thus two mycelia developing from a single spore
are capable of interacting and forming diploid structures after syngamy.
The opposite sexual functions are performed by different cells of a single mycelium.
Perithecium of Neurospora sp.
(the most common homothallic fungi)

5. TYPES OF HOMOTHALLISM
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Primary Homothallism
Secondary Homothallism

6. PRIMARY HOMOTHALLISM
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These fungi are those in which spores are uninucleate.
The nucleus has only one genotype.
Some examples of such fungi are as follows:
Pyronema omphalodes
Puccinia malvacearum
Allomyces javanicus, etc. and many more members of Mucorales.

7. SECONDARY HOMOTHALLISM
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In these fungi, nuclei of compatible mating types are present in each spore.
The spores of these fungi are heterothallic and therefore sexual reproduction
can take place in mycelia produced from a single spore under laboratory
conditions in artificial cultures.
Some examples are as follows:
Neurospora tetrasperma
Coprinus ephimerus

8. HETEROTHALLISM
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In these type of fungal species, hyphae of two different mating species are present, i.e., (+) and (-) strain
is known as heterothallic and the phenomenon is known as heterothallism.
It is derived from the Greek words, “hetero” means other or different and “thallus” means shoot or
thallus.
This term was first used by an American geneticist A.F. Blakeslee in
1904.
These hyphae undergo nuclear fusion to produce zygote.
The hyphae are morphologically similar but physiologically different.
There are no differences between the mycelium of male and female.
They perform differently only in their sexual behaviour.

9. BLAKESLEE’S EXPERIMENT
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Blakeslee proved the phenomenon of heterothallism.
He inoculated spores of two different strains of Mucor hiemalis on a petridish containing synthetic agar medium.
He observed that the zygospores were formed only along the zone of contact of two mycelia.
In another experiment, he did the same thing but here he inoculated only one strain and after some time he
observed that absolutely no zygospores were produced.
Fig: Mucor hiemalis (Zygospore formation indicating
Heterothallism)
Conclusion:
From these experiments he concluded that zygospores could be formed only when mycelia of two different strains
were allowed to come in contact.

10. TYPES OF HETEROTHALLISM:
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Morphological Heterothallism
Physiological Heterothallism
Bipolar Multiple-Allele Heterothallism
Tetrapolar Multiple-Allele Heterothallism

11. MORPHOLOGICAL HETEROTHALLISM :
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It can be defined as the condition when morphologically different male and female sex
organs are produced in two closely associated mycelia.
The two sex organs or gametes are so morphologically different that it is easier to term
one of them as male and the other as female.
Examples: Achlya ambisexualis, Phytophthora palmivora,
Peronospora parasitica

12. BIPOLAR MULTIPLE-ALLELE HETEROTHALLISM:
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This type of heterothallism is controlled by multiple allele at a single locus, instead of a pair of alleles.
For example, if the locus is named as L, the multiple alleles will be designated as L1,L2,L3,L4…Ln and
these are present on the single locus L.
The meiotic division will give rise to thalli which may be of several mating types, generally equal to the
number of alleles. The thallus containing the allele L1 can mate with a thallus of any mating type except
L1.
Similarly L2, can mate with any thallus except that containing L2 allele and so on. In this type of
heterothallism, incompatibility factors are more commonly involved and it is characteristic of
Basidiomycetes except rusts and smuts.

13. TETRAPOLAR MULTIPLE-ALLELE HETEROTHALLISM
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In this type of heterothallism, which is very similar to bipolar multiple allele heterothallism, compatibility
is determined by two loci. Multiple allele- the compatible factor is present on two loci L1 and L2 of two
chromatids of a chromosome. At the time of meiotic division, both the loci are separated with
chromatids. It is estimated that at least 100 alleles are present on each locus.
If the allele composition of the mating type is A1B1, it would be compatible with any other type of allele
composition except A1B1. But the mating type with allele composition is not fully compatible with allele
composition A2B2.

14. REFERENCES:
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https://www.toppr.com
https://www.Your article library.com
https://en.m.wikipedia.org
https://www.sciencedirect.com
https://onlinelibrary.wiley.com
Botany for degree students- B.R.Vashishta and A.K. Sinha

15. THANK
YOU