Heterozygosity of an individual male. The individual male mountain pine beetle (MPB) sequence data used for the assembly was mapped back onto the assembly, and the level of heterozygosity (allelic variation) was determined. Inset, A restricted range of single-nucleotide variant (SNV) density. Red markers indicate scaffolds with very low SNV density, which are hypothesized to represent scaffolds on the ancestral × chromosome portion of the neo-X chromosome. These are the six scaffolds shown in Figure 3.