Encyclopedia of Parasitology

2016 Edition
| Editors: Heinz Mehlhorn

Sex Determination

Reference work entry
DOI: https://doi.org/10.1007/978-3-662-43978-4_2882

In protozoans direct evidence of sexual stages is limited to those species with known gametes (e.g.,  gregarines,  coccidia,  Hypermastigida), but remain scarce in other classes, although in some groups nowadays significant signs of sexuality are noted (e.g., in trypanosomes, gametes). Even in species that form gametes sex determination remains unclear because typical sex chromosomes are not present or not seen (since  chromosomes do not become condensed). In metazoan parasites, however, there is significant genetic sex determination due to the formation and activity of sex chromosomes (heterosomes) in addition to autosomes. The most common system among animals is the XX/XY pattern. Except for a few groups (e.g., Sauropsida) in most animals the 2 X  chromosomeswere found in females (leading to homogametism), while in the male sex the XY situation occurs producing X or Y gametes (heterogametism). Therefore, it is not surprising that in most parasites this XX/XY system occurs...

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© Springer-Verlag Berlin Heidelberg 2016