The distribution of comet tail types in mice with severe NPYq deficiencies. Four types of comet tail were differentiated: 1, short tail; 2, long tail, with majority of DNA still in the head; 3, long tail with DNA evenly distributed through out; 4, long tail with most of the DNA at the distal portion (baloon shape) . The severity of DNA damage increases with tail type, from 1 to 4. Two males were used per genotype; four sperm groups (epididymal, frozen epididymal, testicular and frozen testicular) were examined per male; 100 sperm were scored per group per male. Statistical significance: *P < 0.05; **P < 0.01; ***P < 0.001 (Fisher's two-tailed exact probability test).