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meiosis in apicomplexa

John R. Barta jbarta at uoguelph.ca
Sat May 31 10:49:37 EST 1997

Cliff Monahan wrote:
> I prefer to show my ignorance in the relative obscurity of these pages rather than have
> to do so face-to-face with students. Recently, I couldn't give a good answer on when
> meiosis occurs during the coccidian life cycle. Syngamy is obviously the fusion of
> gametes resulting in a diploid state. Does the haploid state develop immediately
> following syngamy? Furthermore, what is the best explanation for the difference between
> a schizont and a meront -- besides the spelling? Cliff

Meiosis - both ultrastructural (Sinden and colleagues) and genetic
(Shirley et al.) evidence suggests that meiosis occurs immediately after
fusion of the gametes as the first step in sporogony. Thus, all
sporozoites are haploid, as are all other stages of the life history of
the apicomplexan protists.

"Schizont" versus "Meront" - my understanding is that schizogony is a
cellular process in which karyokinesis occurs prior to simultaneous
cytoplasmic fragmentation into multiple progeny.  Typically, the term
schizont has been applied to the asexual stages in the life cycle of
apicomplexan protists and is generally used interchangebly with "meront"
but this is not strictly correct. Many stages in the life history of
apicomplexan protists undergo schizogony (microgamonts, sporonts and
meronts as examples). "Meront" is a more specific term referring to an
_asexual_ stage undergoing schizogony. By analogy, the term "sporogony"
is the specific term for the post-meiotic schizogonic process and the
term "microgametogony" is the specfic term for a schizogonic process
leading to the formation of microgametes.  My preference is that
"schizont" no longer be used and that the more descriptive term "meront"
be used as appropriate. However, there is a lot of history associated
with the term "schizont" and it will take some time to change. 

Hope this helps.



John R. Barta
Dept. of Pathobiology
Ontario Veterinary College
University of Guelph
"jbarta at uoguelph.ca"

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