If the duplicate is redundant and does not provide a fitness benefit, it will be lost by deletion or the accumulation of loss of-function mutations.

A second fate is that a duplicate can simply retain its original function.

TLS Online TPP Program

#Id: 10299

#Section 2: General Biology

Lineage commitment

TLS Online TPP Program

#Id: 10300

#Section 2: General Biology

T-Cell Activation and Differentiation

TLS Online TPP Program

#Id: 10301

#Section 2: General Biology

Three signals are required for activation of a naïve T cell

TLS Online TPP Program

#Id: 10302

#Section 2: General Biology

Positive Costimulatory Receptors: ICOS

ICOS binds to another member of the growing B7 family, ICOS-ligand (ICOS-L), which is also expressed on a subset of activated APCs.

ICOS plays a key role in maintaining the activity of already differentiated effector and memory T cells.

TLS Online TPP Program

#Id: 10303

#Section 2: General Biology

T-cell costimulatory

TLS Online TPP Program

#Id: 10304

#Section 2: General Biology

Negative costimulation