and we’re back! with BRAND SPANKIN' NEW tangents!
welcome redditors!to snoo-finity ... and beyond!

NBME 22 Answers

nbme22/Block 2/Question#31

An unimmunized 1-year-old boy is admitted to the ...

Phase variation

Login to comment/vote.

 +5  upvote downvote
submitted by yotsubato(215),

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 classical mutation rates. Phase variation contributes to virulence by generating heterogeneity. Although it has been most commonly studied in the context of immune evasion, it is observed in many other areas as well and is employed by various types of bacteria, including Salmonella species.

whoissaad  is it the same thing as antigenic variation? +2  
dorsomedial_nucleus  No, antigenic variation involves genomic rearrangement Phase variation can be thought of as MORE or LESS of something. An on/off switch. No DNA is being rearranged, just under or overexpressed in response to the environment. +