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Chapter 22 : Sexual Difficulties

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Sexual Difficulties, Page 1 of 2

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Abstract:

Sex in bacteria is not linked to reproduction—parents passing genes to offspring (via that cycle of sex and reproduction) is the opposite of what we consider to be sex in bacteria. In bacteria, sex is the inheritance of DNA from any source except the parental cell. Asexual reproduction results in an exponential increase in cell numbers: it takes 10 generations to attain 1,000 cell replications and only 70 generations to produce 10 cells, equal to the estimated number of stars in the universe. The generation times of bacteria are short, on the order of hours or days for those species considered to be "slow growing." Therefore, relatively little time is needed for cell numbers to reach the point where each nucleotide in a genome has been subjected to at least one mutation. Transformation is the uptake of DNA from the environment. Any advantage tendered by acquired DNA is secondary to the real reason that bacterial sex evolved. If a gene is acquired from a divergent source, both the donor and recipient can have identical copies despite the fact that the organisms themselves are unrelated. Expanding this to the point where every gene has the potential to transfer to any organism from any source, and this might cause some systematists to lose sleep: rampant gene transfer would render useless their efforts to assign microbes to meaningful groups and to reconstruct the evolutionary links between organisms, since the closest relatives may be no longer be the most closely related.

Citation: Ochman H. 2012. Sexual Difficulties, p 159-163. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch22

Key Concept Ranking

DNA
0.5673076
Genetic Variation
0.47830147
Chromosomes
0.4524694
Bacterial Evolution
0.42963165
0.5673076
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Figure 1

Conjugation in bacteria and that in humans both involve physical contact between the DNA donor (central cells in bacteria; tall fellow in humans) and a recipient. The round afterglow spot observed in the bacterial recipients—outer cells—denotes a successful DNA transfer event. Micrograph courtesy of Ana Babic, INSERM. doi:10.1128 /9781555818470.ch22f1

Citation: Ochman H. 2012. Sexual Difficulties, p 159-163. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch22
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