With the extension over time, this is also the result of the first cycle, and so is \sigma^2_1 (for brevity). At cycle 2, this variance is generated yet again—this time becoming the de novo variance ( \Delta \sigma^2 )—and accumulates to what was present already—the "carry-over" variance. The second cycle variance ( \sigma^2_2 ) is the weighted sum of these two components, the weights being 1 for the de novo and \left( 1 - \tfrac{1}{2N} \right) = \left( 1 - \Delta f \right) for the"carry-over".
