Two ways to make an mtDNA bottleneck

Rapid changes in mitochondrial DNA allele frequency between generations have been explained by an 'mtDNA bottleneck' in the germ line, and it has recently been proposed that mtDNA aggregates, or nucleoids, drive such a bottleneck. Now, a new study finds a sharp reduction in mtDNA content in the germ line and suggests that such reduction alone may account for the bottleneck effect.