Avian and Poultry Biology Reviews 13 (2), 2002

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Sex determination and sex differentiation

Kiyoshi Shimada*
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601, Japan

ABSTRACT

Recent advances in studies on molecular mechanisms of sex determination and sex differentiation in birds are reviewed. The gonad in embryo carrying ZZ chromosomes differentiates into the testis, whereas those carrying ZW chromosomes into the ovary. Although sex-determination gene(s) has not been identified, Dmrt-1gene located on the Z chromosome may lead to male determining pathway, provoking gene expression of Anti-MÏllerian hormone and Sox 9 for testis formation and male phenotypic characterization. In the ZWfemale embryo, absence or low expression of Dmrt-1may be associated to expression of P450 aromatase for estrogen production and consequent ovary formation.

Keywords: sex determination, sex differentiation, gonad, Dmrt-1, Anti-MuÈllerian hormone, Sox 9, aromatase, testis, ovary.

Production of germ-line chimeras and their application in domestic chicken

Atsushi Tajima*
Institute of Agriculture and Forestry, University of Tsukuba, Ten-noh Dai 1-1-1, Tsukuba, Ibaraki 305-8572, Japan

Keywords: PGCs, germ-line chimera, chicken

Reproductive maturity of turkey hens: egg composition, embryonic growth and hatchling transition

Todd J. Applegate*
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-1151

ABSTRACT

Selection for body weight in commercial turkey strains has resulted in faster growing turkeys with improved feed efficiencies. These genetic gains, however, have come largely at the expense of reproductive fitness. In particular, considerable variability exists in early egg production. This variation greatly impacts egg composition, which in turn can affect embryonic growth and post-hatching transitions from an embryonic lipid-based metabolism to a glucose-based metabolism. Notably, embryos from young hens develop more slowly than embryos from older hens during the last week of incubation. Further studies have shown that these developmental differences are in part due to a proportional increase in yolk mass in eggs from older hens; which allows for a greatermass transfer of yolk lipid to the embryo during the finalweek of incubation. Hypothetically, developmental differences during incubation may contribute to problems that occur during the acclimation period after hatching, especially if hatchlings come fromvery young hens.

Keywords: Egg, embryo, hen, poult, reproduction, turkey