Fig. 1.
The relationship between the number of genes per chromosome (NG) over chromosome length (LC) shows a strong correlation in nonmammals, irrespective of genome size, chromosome number and taxonomy. In noneutherian genomes, the slope of the trend-line can be interpreted as measurement for genome-compactness. The small R2-value in zebrafish (Danio rerio; 0.37) can be explained by two outlier chromosomes, that of medaka (Oryzias latipes; 0.48) by the relatively equal size of its chromosomes and variance in the number of genes. The somewhat smaller R2-value observed in Caenorhabditis elegans (R2 = 0.65) is due to the relatively even length of its chromosomes (Nelson et al. 2004), which makes it difficult to test for a linear relationship between NG and LC