Generalized Life Cycle of the Sac Fungi
Developmental stages of an ascus - a saclike cell in which haploid spores (ascospores) are produced.
See below the diagram for a description of the flow chart.
The flow chart above illustrates the following: Ascospores 
germinate and develop into mycelia 
. At this stage,
these mycelia can produce more mycelia, then produce conidia
which can produce more conidia and eventually spores. This repetitive
cycle is the asexual cycle. Some mycelia as they age form two
kinds of gametangia, the female organ, ascogonium 
and the male
organ, antheridium . The antheridium attaches itself to the ascogonium
by means of a receptive hyphal branch, known as the trichogyne 
and
transfers its nuclei to it 
. This process which is called plasmogamy
(the transfer of protoplasm and nuclei which do not fuse),
stimulates the ascogonium to produce binucleate hyphae 
. The
binucleate hyphae, known as dikarya become septate 
and bend at
the tip to form a hook cell 
. (See the flow chart below).
The flow chart below illustrates the following: The nuclei in the hook cell divide 
and form septa. The
septated entity forms three cells 
, a uninucleate basal cell, a
uninucleate apical cell and a binucleate ascus mother-cell. The
nuclei in the ascus mother-cell fuse (karyogamy) 
. The resulting
zygote nucleus in the young ascus is the only diploid nucleus in the
entire life cycle of the filamentous Ascomycetes. Meiosis then takes
place and forms a tetrad of nuclei followed by mitosis. This
last division is necessary for the development of a mature ascus
with ascospores (see green letter "E"). The process described here, A - E, takes place in the fruiting body indicated
in the top flow chart as red circle 8.
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