Use the following information as background for the next few questions.
Immunodeficiencies can be genetic in origin,and two examples are Bruton's agammaglobulinemia,an X-linked disorder,and DiGeorge syndrome,caused by a deletion from chromosome 22.Bruton's disorder results in underdeveloped B cells,whereas DiGeorge syndrome results in a missing or seriously underdeveloped thymus.
-Assume that a DiGeorge syndrome-like phenotype was produced in a specific "gene-knockout" mouse,one lacking expression of HA3,a Hox gene known to be involved in developmental regulation in the mouse.
The phenotype of the HA3 knockout can be ascertained by