Data of 29,879 birds pertaining to 8 generations, from 2010 to 2018 on growth line (PB1) of IBL-80 broiler were collected for present study. The mean estimates of growth and fertility traits indicated higher growth performance of PB1 affected its fertility performance. ADG5 had highest estimate indicating higher growth during grower phase, ADG for all other ages were comparable. Least squares analysis indicated that effect of gender, month of hatch and generation were significant (p<0.01) for all growth and fertility traits. AIREML heritability estimates indicated appreciable additive variance in BWT0, BWT5 and ADG5. Other growth and fertility traits had lower heritability. Phenotypic and genetic correlation estimate indicated negative association between growth and fertility traits. Gompertz growth curve had moderate R-square (42%), and the IPw and IPt estimates were 1289.34 grams and 4.80 weeks, respectively. PCR-RFLP study of IGF1 promoter identified frequencies of AA (0.79), AC (0.18) and CC (0.03) genotypes. CC homozygotes were lower with respect to their performance in growth and fertility traits. Sequencing results of both alleles revealed T>G transversion at 244 position in C allele. Gene regulation analysis confirmed that such transversion resulted in non-binding of Oct-1 transcription factor at 241 to 250 bp in C allele, causing down regulation of the gene. Alignment results also revealed deletion of a pyrimidine base (C) at 567 position in both A and C alleles in eight samples, which caused non-binding of CRE-BP1 transcription factor at 565 to 574 bp promoter region. The mutations and deletion in the promoter sequence affected the transcriptional gene regulation affecting growth and fertility performance.