The paragraph beginning at the bottom of p. 109 should read:

Mice arising from a cross of a wild-type with a chimera contributing a germ cell with a targeted mutation will be heterozygous for that mutation. These mice may or may not have an altered phenotype. Heterozygous mutant mice still have one functional copy of the gene being targeted, which is often sufficient to produce a normal phenotype. The most interesting and informative phenotype is generally produced by mating heterozygous gene-targeted mice to produce some mice that are homozygous for the mutation, meaning that they have no normal copies of the targeted gene. These homozygous mice are often severely affected and may even die in utero or shortly after birth. The lab animal technician can play a critical role in breeding such mice by carefully observing the phenotypes of pups, and alerting the researchers to any unusual findings. Additionally, these mice require special and attentive care.

The acknowledgments list is incomplete; these contributors were inadvertently left off:

Educational Resources Committee
James Magrath, LATG

Contributors and reviewers:
Allison Bright, LATG
Bradley Fisher, LATG
Diana Lancaster, LATG
Jan Parker-Thornburg, PhD
Sarah Rovezzi, LATG
Ryan Sumpter, MS, RLATG
Melissa Williams, LATG

Images:
Jan Parker-Thornburg, PhD