The fact that b cells and t cells are both clonally selected means that each b cell or t cell produces only one kind of antibody. there are five different types of immunoglobulin. each individual can form many different antibodies, but only one type of t cell receptor. specific t cells and b cells increase in number on recognition of an epitope. b cell lymphocytes change their antibody specificity to match a newly discovered antigen, then undergo mitosis to form a clone of plasma cells.

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.