Phase variation or phenotypic switch allows the expression of a given phenotype to be switched ON or OFF. Antigenic variation refers to the expression of a number of alternative forms of an antigen on the cell surface, and at a molecular level, shares common features with phase variation mechanisms.
How does antigenic variation occur?
Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence cassettes.
What does phase variable mean?
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.
What is the major source of variation in bacteria?
Bacteria mainly reproduce asexually. Cells enlarge, copy their DNA, and divide into two new cells. The only source of variation, therefore, is mutation, and each mutation must accumulate with other mutations, one after another, before a new combination of genes is possible. This takes a long time.
How do bacteria increase their genetic variation?
There are three mechanisms of horizontal gene transfer typically used by bacteria: transformation, transduction, and conjugation. Transformation allows for competent cells to take up naked DNA, released from other cells on their death, into their cytoplasm, where it may recombine with the host genome.
What are phase variable genes?
Phase-variation of genes is defined as the rapid and reversible switching of expression — either ON-OFF switching or the expression of multiple allelic variants. Switching of expression can be achieved by a number of different mechanisms.
What is antigenic variation in trypanosomes?
Trypanosome persistence in the mammal is due to antigenic variation, which involves changes in the identity of the variant surface glycoprotein (VSG) that forms a dense cell surface coat to shield invariant surface antigens from immune recognition.
What is the definition of pyrogenic?
Definition of pyrogenic 1 : of or relating to igneous origin. 2 : producing or produced by heat or fever.
What does direct variation mean in math?
Direct variation. A direct variation (D.V.) is a relationship between two variables x and y that can be written as. y = kx, k ≠ 0. This situation occurs when the ratio of two variables is constant.
What is the medical definition of diphasic?
Medical Definition of diphasic. a : exhibiting a stage of stimulation followed by a stage of depression or vice versa the diphasic action of certain drugs b : relating to or being a record of a nerve impulse that is negative and positive…
What is the difference between joint variations and direct variations?
So the behavior of the variables is just the opposite of direct variations. Therefore, if X is in indirect variations with Y, then you can symbolically write it as X α 1Y. If more than two variables share a direct relationship or one variable changes with the change product of two or more variables, it is joint variations.
What are variations in math?
However, others are the variables which change in different situations. The changing of variable parameters is often gone by the term variations or algebraic variations. Let’s explain with an example of a simple equation y = mx wherein m refers to a constant.
