Directional Selection Is Best Described as

Multiple Choice

Directional selection is best described as

A) all polymorphic alleles preserved in a population
B) T-cell receptor interaction with peptide:MHC complexes directed to a planar interface
C) a mechanism in T cells that is analogous to affinity maturation of immunoglobulins
D) selected alleles increase in frequency in a population
E) selection of most appropriate transplant donor directed at the identification of identical or similar combinations of HLA alleles compared with the transplant recipient.