Gene number expansion and contraction in vertebrate genomes with respect to invertebrate genomes

The boxplot of the average vertebrate family sizes (n_v) grouped by the largest family size of homologous genes in the six invertebrate genomes and by the number of the invertebrate genomes where homologous copies can be found. The X-axis shows the largest family size of homologous genes in the six invertebrate genomes (singletons, two-gene families, and multigene families are represented by light-gray, medium gray, and dark-gray, respectively) and also the number of the invertebrate genomes in three groups (present in only one or two invertebrate genomes, in three to five invertebrate genomes, or in all six invertebrate genomes).