Why does the DNA of Bacillus subtilis not contain DNA families of 20-37 members? I am reading the book "Molecular biology of the Cell, 6th edition" and in chapter one page 18 the following figure is included ![enter image description here]( I am presuming this figure represents all genes within the Bacillus subtilis, which makes me wonder: why are there no families with 20-37 genes? There is a group for 4-19, and one for 38-77. What happened to all sizes in between?

Based on the paper (open access) from which this figure was adapted, the 38-77 group consists of 5 gene families with 38, 47, 57, 64 or 77 members. In contrast, there are 284 “families” with 2 members, 91 with 3 members, 42 with 4 members, 25 with 5 members, etc. This is clearer in the original figure:

![enter image description here](

Thus the larger gene families are outliers and there simply exists no gene families in _B. subtilis_ with 20-37 genes (at least by the methodology of this paper).