Relative levels of basal expression for CYP1 and AHR1 mRNA in early chicken embryos.

Whole-body samples of unexposed chicken embryos were collected on developmental days 1, 2, 3, 5, and 7 and analyzed by real-time RT-PCR. Data were normalized (calculated by E−ΔCt) and results are shown as percentage of the CYP1B1 mRNA level (n = 3). The embryos analyzed were staged according to Hamburger and Hamilton [63] and http://msucares.com/poultry/reproductions/poultry_chicks_embryo.html: Day-1 samples were taken after 31 h of incubation (stage 9, seven somites). At this stage the nervous system, eye, and heart have begun to develop. On day two (sampled at 50 h: stage 16, 19–22 somites) heart beats can be observed. On day three (sampled at 74 h: stages 20–21, 40–43 somites) nose, legs, and wings begin to appear. On day five (stage 27) the beak and reproductive organs start to form and sex differentiation occurs. On day seven (stage 31) feather papillae begin to appear.