This series of videos explains the research on Drosophila flies which led to an understanding of the way that concentration gradients of gene transcription factors can switch on genes and lead to specialisation of cells in early embryo development .[stop the video at 4 minutes][Stop the video at 18m:50s][Stop the video at 21 minutes]In an early-stage embryo the production of unspecialized cells is followed by their development...