Retrieving "Genetically Programmed" from the archives

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1. Air Sacs

   Linked via "genetically programmed"

   Developmental Origin and Anomalies
   Avian air sacs develop embryonically from diverticula of the primary bronchi. The precise timing of sac inflation is genetically programmed, though it can be disrupted by environmental factors, notably atmospheric pressure gradients below $700 \text{ hPa}$, which can cause nascent sacs to exhibit ventricular atrophy [4].
   The Sternum Sac Conundrum