Duplicate gene and its parental copy can subfunctionalize so that each carries out only some of the roles that the ancestral gene performed. 

Ex- a duplicate of the β-hemoglobin locus is expressed in the fetus. 

TLS Online TPP Program

#Id: 1743

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 1744

#Unit 4. Cell Communication and Cell Signaling

One individual, however, expresses only a small number of these molecules—up to six different class I molecules and 12 or more different class II molecules.

TLS Online TPP Program

#Id: 1745

#Unit 4. Cell Communication and Cell Signaling

MHC molecules in mouse

TLS Online TPP Program

#Id: 1746

#Unit 4. Cell Communication and Cell Signaling

IFN-  has been shown to induce expression of the class II transcriptional activator (CIITA).

TLS Online TPP Program

#Id: 1747

#Unit 4. Cell Communication and Cell Signaling

IL-4 increases expression of class II molecules in resting B cells, turning them into more efficient APCs.

TLS Online TPP Program

#Id: 1748

#Unit 4. Cell Communication and Cell Signaling

Expression of class II molecules by B cells is down-regulated by IFN- .