The role of gravity in chick embryogenesis

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Abstract
Thirty fertilized chick eggs preincubated for 0, 7 and 10 days on earth (10 eggs each) were flown in the space shuttle ‘Endeavour’ and further incubated for 7 days under microgravity. Twenty out of thirty eggs ( ten‐day‐old; 10/10 seven‐day‐old; zero‐day‐old) were recovered alive after landing. The only living embryo of the zero‐day‐old group died 24 days after launch, and was comparable to a 16‐day‐old embryo. The high mortality of the 0‐day‐old eggs appeared to be related to the specific inner structure of the egg. Simulation experiments performed on earth indicated that when yolk stayed in the albumen for more than 2 days, most of the embryos died. The subtle difference in specific gravity between the yolk (1.029) and albumen (1.040) plays a critical role in early chick embryogenesis.