Q1. When did dinosaurs and pterosaurs become extinct? Which are the only extant animals that descended directly from dinosaurs?

Q2. They started with a stain of mouse in which the heavy chain and light chain loci had been `knocked-out" (made non-functional). They then introduced into embryos from these mice genes for heavy and light chains from humans; transgenic mice were then grown from these embryos. When exposed to antigens, these mice produce human antibodies against the antigens. A. Why was it required to start with Ig knock-out mice? B. The antibodies produced from the transgenic mice are `human" antibodies; how do these differ from the antibodies to the same antigen from normal mice? C. Would the transgenic mice recognize antigens as foreign differently as normal mice?