Figure 35.16 Consequences of gene disruption by recombination. Sections of muscle from normal (A) and gene-disrupted-by-recombination (B) mice, as viewed under the light microscope. Muscles do not develop properly in mice having both genes for myogenin disrupted. Arrows indicates bones of the pelvis, establishing that the two views show the same anatomical region. M in part B indicates a muscle fiber in the knockout mouse.