Figure 1.

Overview of the reproductive system and embryonic development in chicken. Avian ovary contains large number of preovulatory follicles, small white follicles (SWF, 1–2 mm), large white follicles (LWF, 3–5 mm), and small yellow follicles (SYF, 6–10 mm), and approximately five prehierarchical follicles, naming F1 to F5, depending on their sizes. After ovulation, F1 follicles enters the avian oviduct and fertilizes in the infundibulum. After passing magnum and isthmus, a one-cell zygote starts first cleavage in the uterus and becomes an Eyal-Giladi and Kochav stage (EGK)-X blastoderm, having approximately 55,000 cells at the time of oviposition.