Ornithine decarboxylase: haplotype structure and trait associations in White Leghorn chickens

Department of Animal Science, McGill University, Ste. Anne de Bellevue, QC, Canada H9X 3V9.

Sequence analysis of 4,230 bp of the 3' end of the ornithine decarboxylase gene of 20 chickens from a noninbred White Leghorn strain revealed a total of 62 polymorphisms. Of these 61% were transitions, 24% were transversions, and 16% were deletions or insertions. Despite the high number of polymorphisms, only 3 haplotypes were present among the 40 alleles analyzed. Based on the genetic distances between haplotypes they segregated early during domestication of the chicken. Ornithine decarboxylase is a pivotal enzyme in regulating the synthesis of polyamines, cations that are important regulators of cell division, differentiation, and apoptosis. Variants of ornithine decarboxylase are, therefore, expected to affect many different traits. Association analyses between genotypes and the major egg production traits in female chickens of the same strain revealed significant effects on the onset of sexual maturity, BW at sexual maturity, eggshell thickness (a measure of calcium deposition), and residual feed consumption (a measure of the metabolic rate). Further, comparisons of the genotypes indicated that the 3 haplotypes differ in their phenotypic properties. Our results show that variations in a gene that is ubiquitously expressed in all cells of an organism may nevertheless contribute to distinct phenotypic properties of the organism as a whole.