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In biology, phase variation is a method for dealing with rapidly varying environments without requiring random mutation. It involves the variation of protein expression, frequently in an on-off fashion, within different parts of a bacterial population. As such the phenotype can switch at frequencies that are much higher (sometimes >1%) than ...
However, in many bacterial pathogens, mod genes contain simple sequence repeats (SSRs), and the associated restriction enzyme encoding gene (res) is inactive. In these organisms the DNA methyltransferase phase varies between two states (ON or OFF) by variation in the number of SSRs in the mod gene. [9] Multiple different mod genes have been ...
English: Phase and Antigenic Variation in Bacteria. pA is the promoter for FimA, pB is the promoter for FimB and pE is the promoter for FimE. IRR is inverted repeat right and IRL is inverted repeat left.
Griffith's experiment discovering the "transforming principle" in Streptococcus pneumoniae (pneumococcal) bacteria.. Griffith's experiment, [1] performed by Frederick Griffith and reported in 1928, [2] was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation.
There are two popular and overlapping theories that explain the origins of crossing-over, coming from the different theories on the origin of meiosis.The first theory rests upon the idea that meiosis evolved as another method of DNA repair, and thus crossing-over is a novel way to replace possibly damaged sections of DNA. [9]
In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploid asexual phase – the sporophyte. A mature sporophyte produces haploid spores by meiosis, a process which reduces the number of chromosomes to half, from two sets to one. The resulting haploid spores germinate and grow into ...
With phase variation, B. intestinalis can maintain subpopulations both resistant and susceptible to phage infection, thereby generating a unique environment in which crAss001 has consistent access to hosts (susceptible subpopulation) and B. intestinalis can replicate uninhibited by phage (resistant subpopulation). [13]
The G1/S cell cycle checkpoint controls the passage of eukaryotic cells from the first gap phase, G1, into the DNA synthesis phase, S. In this switch in mammalian cells, there are two cell cycle kinases that help to control the checkpoint: cell cycle kinases CDK4/6-cyclin D and CDK2-cyclin E. [ 1 ] The transcription complex that includes Rb and ...