What causes the sexuality of an organism
The evolution of sexual reproduction
Gunnar Bartsch Press and public relations
Julius Maximilians University of Würzburg
How did sexual reproduction come about? There are different views in science on this question. Researchers from Würzburg, Kiel and Lyon have now discovered traces that could put an end to the discussion.
Every organism strives to reproduce and to pass on its own genetic material to the next generation. From what is known as asexual reproduction, in which a genetically identical descendant is descended from a living being, sexual reproduction emerged in the course of evolution. The prerequisite for this was the development of two different sex cells whose genes can be exchanged and recombined in the next generation. Offspring that result from sexual reproduction through the fusion of an egg cell and a sperm therefore have a unique combination of paternal and maternal genes.
The body cells of most living things have a double set of chromosomes, called "diploid" in technical terms. In order for this to be preserved over the generations, the chromosome set of the sex cells is halved in a special form of cell division - meiosis - during their maturation, they are then haploid. Through the fusion of two haploid sex cells during sexual reproduction, the original diploid chromosome set is restored in the embryo.
Dispute over the origin of meiosis
Although meiosis proceeds very similarly in all living beings that reproduce sexually, the history and evolutionary origin of this process are still unclear. There is one main reason for this: the synaptonemal complex, a structure that is responsible for ensuring that the double set of chromosomes is halved without errors during meiosis, is made up of apparently unrelated proteins in various developmental model organisms.
"This fact has long been seen as an indication of the hypothesis that the complex and thus parts of meiosis developed independently of one another in evolution," explains Ricardo Benavente, Professor at the Department of Cell and Developmental Biology at the University of Würzburg.
On the other hand, there was the previously unproven hypothesis that the synaptonemal complex developed only once in the history of sexual reproduction and later developed apart in the various species.
New evidence of the unique creation
The working groups around Professor Ricardo Benavente and the private lecturer Dr. Manfred Alsheimer at the Biozentrum of the University of Würzburg, together with researchers from the Universities of Kiel and Lyon, has now succeeded in identifying related proteins of individual components of the synaptonemal complex of the mouse in the freshwater polyp Hydra, one of the first multicellular animals to have evolved. These proteins have the same evolutionary origin as mammalian proteins, which dates back over 500 million years - at the origin of multicellular animals.
Conclusion: "The work refutes the old hypothesis on the evolution of the synaptonemal complex and provides new evidence for a unique development of meiosis in the evolution of sexual reproduction," says Johanna Fraune, doctoral student and first author of the work.
The research work in Würzburg is funded by the priority program 1384 "Mechanisms of Genome Haploidization" of the German Research Foundation (DFG). The working group has been a member of the program since it was founded in 2009.
“Hydra meiosis reveals unexpected conservation of structural synaptemal complex proteins across metazoans”, Johanna Fraune, Manfred Alsheimer, Jean-Nicolas Volff, Karoline Busch, Sebastian Fraune, Thomas Bosch & Ricardo Benavente. PNAS / USA doi: 10.1073 / pnas.1206875109 (2012)
Dipl.-Biol. Johanna Fraune, T: (0931) 31-84583
Email: [email protected]
PD Dr. Manfred Alsheimer, T: (0931) 31-84282
Email: [email protected]
Prof. Dr. Ricardo Benavente, T: (0931) 31-84254
Email: [email protected]
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