Knockout mice have been genetically altered to knock out specific genes....
 

...How are these mice most often .......? Knockout mice have been genetically altered to knock out specific genes. How are these mice most often used in research?

A.to examine defects in DNA structure in those regions that have been altered
B.to determine the role of proteins coded for by those genes that are knocked out
C.to study DNA replication in the defective genes (those that have been altered)
D.to study the effect of radiation on DNA

The answer is B. Anytime you knock out a gene you are trying to find out what that gene or protein codes for by studying the phenotypes or lack thereof that result.

definitely B