Freezing during the training day in different ITIs and in the baseline period for female (A) and male (B) Ts65Dn mice and 2N controls are presented. In both genders, there was no significant effect of genotype in acquisition of the task. Total freezing in testing days (C and D) indicates that there was no statistically significant difference between genotypes in tone-cued fear conditioning, but in both sexes, Ts65Dn mice showed deficit in contextual fear conditioning. In the fear conditioning test, n=10 for both 2N and Ts65Dn female mice and n=21 for male 2N and n=17 for male Ts65Dn mice (*=p<0.05). In the startle response test, no significant effect of genotype was seen in both female (E) and male (F) mice. In the startle response test, n=8 for all groups. Results are presented as Mean ±/+ SEM.