The Effect of the Kn Gene on the Sexual Development of Cockerels1>2

ABSTRACT The sexual development of cockerels of three feather growth rate genotypes, k+/k+, Kn/k+, and K"/Kn, was studied at 2-week intervals from ages 1 to 31 weeks. Body, testis, and comb weights were collected. Histologic evaluation of testes and semen fertility tests were also made. The K " gene, when homozygous, delayed body growth, and testis growth and development in homozygous males, thus delaying their sexual maturity 2 to 3 weeks. Body weights, relative testis weights, and seminiferous tubule diameters were similar for the k+/k+ and Kn/k+ males but significantly different from the K^/K " males. Stages of spermatozoic development were not significantly different between males of any of the genotypes. Regressions of relative testis weight on body weight and of seminiferous tubule size and stage of spermatozoic development on relative testis weight were not different for any of the genotypes. Relative comb size was significantly different between males of all three genotypes. When regressed against relative testis weight, the K^/K " males were significantly different from the other two groups of males. The K12 gene exerted an influence, directly or indirectly, which appeared to reduce testosterone production in the IC/KV males. The nature of the K " gene's action was not evident from these data, nor was it clear whether it was acting on the Leydig cells of the testes or on the lutinizing hormone producing cells of the pituitary