The asexual ploidy cycle and the origin of sex

SEX involves syngamy (gamete fusion), which doubles the amount of DNA in a cell, and meiosis1, which halves it. The result is a 'ploidy cycle' of alternating diploid and haploid phases. Asexual reproduction does not require changes of ploidy, and yet asexual forms may have ploidy cycles. Here I show that such cycles lessen the mutation load, compared with permanent diploidy or poly-ploidy, and are thus likely to evolve in cases where it is always advantageous to have more than one copy of the genome per cell. The asexual ploidy cycle could have facilitated the origin of sex, by providing a means of orderly genetic reduction available im-mediately after the origin of syngamy.

[1]  M. Hasegawa,et al.  Protein phylogeny gives a robust estimation for early divergences of eukaryotes: phylogenetic place of a mitochondria-lacking protozoan, Giardia lamblia. , 1994, Molecular biology and evolution.

[2]  James F. Crow,et al.  Genetic Loads and the Cost of Natural Selection , 1970 .

[3]  L. Niilo.  Progress in Protozoology , 1970, Nature.

[4]  A. Kondrashov.  Selection against harmful mutations in large sexual and asexual populations. , 1982, Genetical research.

[5]  M. Kimura,et al.  The mutational load with epistatic gene interactions in fitness. , 1966, Genetics.

[6]  Mutational load and the advantage of sex , 1984, Heredity.

[7]  K. Grell.  The Protozoan Nucleus , 1964 .

[8]  W. M. Lewis.  Nutrient Scarcity as an Evolutionary Cause of Haploidy , 1985, The American Naturalist.

[9]  Sergei Ju. Afon’kin.  Spontaneous “Depolyploidization” of Cells in Amoeba Clones with Increased Nuclear DNA Content , 1986 .

[10]  Ken-ichi Kojima,et al.  Mathematical Topics in Population Genetics , 1970 .

[11]  F. Siemensma,et al.  A Multinucleate Amoeba, Parachaos zoochlorellae (Willumsen 1982) comb, nov., and a Proposed Division of the Genus Chaos into the Genera Chaos and Parachaos (Gymnamoebia, Amoebidae) , 1987 .

[12]  H. Bernstein,et al.  Aging, sex, and DNA repair , 1991 .

[13]  A. Knoll,et al.  The early evolution of eukaryotes: a geological perspective. , 1992, Science.

[14]  Mark Kirkpatrick,et al.  Genetic segregation and the maintenance of sexual reproduction , 1989, Nature.

[15]  H. L. Carson,et al.  The Genetics and Biology of Drosophila , 1976, Heredity.

[16]  A. Kondrashov,et al.  Mutation load under vegetative reproduction and cytoplasmic inheritance. , 1994, Genetics.

[17]  Ļ. Cleveland.  The Origin and Evolution of Meiosis. , 1947, Science.

[18]  T. J. Byers,et al.  Molecular biology of DNA in Acanthamoeba, Amoeba, Entamoeba, and Naegleria. , 1986, International review of cytology.

[19]  L. Hurst,et al.  A note on the evolution of meiosis. , 1991, Journal of theoretical biology.

[20]  L. Margulis,et al.  Origins of Sex , 1987 .

[21]  C. Cantor,et al.  Giardia lamblia: haploid genome size determined by pulsed field gel electrophoresis is less than 12 Mb. , 1991, Nucleic acids research.

[22]  A. Kondrashov,et al.  Classification of hypotheses on the advantage of amphimixis. , 1993, The Journal of heredity.

[23]  G. Bell,et al.  Sex And Death In Protozoa , 1988 .

[24]  Drunken walk of the diploid , 1993, Nature.

[25]  A. Kondrashov.  Deleterious mutations and the evolution of sexual reproduction , 1988, Nature.

[26]  D. Haig.  Alternatives to meiosis: the unusual genetics of red algae, microsporidia, and others. , 1993, Journal of theoretical biology.

[27]  M. Maguire,et al.  The evolution of meiosis. , 1992, Journal of theoretical biology.

[28]  B. Charlesworth,et al.  Unravelling the Evolutionary Advantage of Sex : a Commentary on ' Mutation–selection Balance and the Evolutionary Advantage of Sex and Recombination ' , 2022 .

[29]  J. Drake.  A constant rate of spontaneous mutation in DNA-based microbes. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[30]  G. Brugerolle.  Evolution and Diversity of Amitochondrial Zooflagellates , 1993 .