The cardiac neural crest (CNC) plays a central role in development of the thymus gland and cardiovascular system. Through morphological and histological characterization of embryos homozygous for the Del(7)Tyr(c-112K) and Del(7)Tyr(c-3H) albino deletions, we identified abnormalities that are consistent with aberrant development of tissues requiring CNC contributions. The defects include incompletely penetrant heart and great vessel patterning defects and hypoplastic thymus glands. The CNC phenotype is complemented by the partially overlapping deletion Del(7)Tyr(c-23DVT). Combined, these results suggest that a functional region necessary for development of CNC derived tissues is located between the Del(7)Tyr(c-23DVT) and Del(7)Tyr(c-112K) distal deletion breakpoints. This interval encompasses a functional region previously identified as important for juvenile survival (juvenile development and fertility, jdf). Using deletion mapping, we localized the Frizzled4 (Fzd4) gene to the jdf/thymus and cardiac development intervals.