All of 23andMe's independent directors resigned from its board this week, a rare move that marks the latest challenge for the genetic-testing company. The resignations follow drawn-out negotiations with 23andMe CEO and co-founder Anne Wojcicki, who wants to take the company private. In a Tuesday letter addressed to Wojcicki, the seven directors said they had yet to receive a “a fully financed, fully diligenced, actionable proposal that is in the best interests of the non-affiliated shareholders” from the chief executive after months of efforts.