Syrian government forces have left the southern city of Sweida, where days of sectarian clashes involving the Druze minority have left hundreds dead. Interim President Ahmed al-Sharaa made a call for unity in the middle of the night.Also in the programme: proof that a technique using genetic material from three people to create embryos is leading to children born free of incurable and devastating mitochondrial disease; and an interview with Columbia University graduate Mahmoud Khalil, who was detained for more than 100 days after taking part in pro-Palestinian demonstrations on campus.