Phenotypic Analysis of Perinatal Lethality in Mice.

If homozygous mutants are found dead shortly after birth, further analysis of the phenotype will depend on knowing whether death occurred before or after parturition, which marks a major shift in physiological conditions of neonates. This overview provides methods for determining the time of death and discusses possible causes of lethality during this period, including catastrophic morphological abnormalities or developmental delay of some or all organs. Attention is given to specific defects that could result in perinatal death, such as cranial nerve defects, cleft palate, diaphragm defects, and other problems that might not have been relevant during intrauterine development but become critical during the transition to extrauterine existence.