Comparative Sex Chromosome Genomics in Snakes: Differentiation, Evolutionary Strata, and Lack of Global Dosage Compensation
Figure 2
Mapping of the best candidate female-specific W-candidate scaffolds of (A) boa, (B) garter snake, and (C) pygmy rattlesnake to the Anolis macrochromosomes.
The histograms (left) show the number of candidate W scaffolds mapped to the six major chromosomes of Anolis, with the green bar highlighting the Anolis homolog to the snake Z chromosome. The W candidates homologous to Z-linked scaffolds (which accounts for 7.6% of the genome) make up 49% and 35% of all female-biased scaffolds in pygmy rattlesnake and garter snake, respectively. This is a 6.4-fold excess in pygmy rattlesnake, and 4.5-fold excess in garter snake over random mapping based on chromosome size. In contrast, in Boa, only 6.5% of scaffolds map to chromosome 6, which does not differ from random mapping on the basis of chromosome size. The right panel shows color-coded mapping density of W-candidates along the Anolis macrochromosomes. The density of W-candidates is not uniform across the Z chromosome in both pygmy rattlesnake and garter snake (p<0.0001 for mean nearest neighbor distances). The data in this figure are from all female biased candidate W-linked scaffolds and will thus contain both non-coding scaffolds as well as scaffolds containing protein coding genes.