A Ser162/Gly162 polymorphism in Japanese quail ovomucoid

Japanese quail ovomucoid exists in two polymorphic forms. One has serine, the other glycine at position 162. The tryptic peptide corresponding to positions 160 to 164 was purified from ovomucoids isolated from egg whites of eggs laid by 11 different hens and subjected to amino acid analysis. The quantitative distribution of serine and glycine in this pentapeptide is consistent with the interpretation that the ovomucoid gene exists in two codominant allelic forms at one locus. Even though the gene product is apparently expressed only in the female, these results indicate that the ovomucoid structural gene is transmitted as a simple Mendelian character which is neither sex-linked nor shows dominance. Intact third domains (positions 131 to 186) isolated from the two allelic forms of ovomucoid interact with bovine beta-trypsin in a similar but not identical manner; the complex with the glycine form dissociates more rapidly. Evidence is presented which suggests that glycine is the ancestral residue at position 162; yet, the serine form is the more frequent phenotype.