Table 1.

Numerical summary of results

	Total number	Number in genera with more than one sequenced genome	Number conserved in at least one other genome within genus	Number predicted to be horizontally acquired by Alien Hunter
Class 1 orphan MTa	558	367	269	189
Class 2 orphan MTa	160	132	110	31
R–M MT	196	169	112	80
R-E	215	N/A	N/A	N/A
Orphan MTs associated with degraded REb	174	121	68	83
Orphan REs associated with degraded MTb	15	N/A	N/A	N/A
Fully degraded R–M systemsc	222	N/A	N/A	N/A

^aOne gene from each of these headings also match against an RE in the reference sequence. However, these two instances do not affect any of our results.

^bThese genes are present in the set of MT or RE homologues identified at e-value ≤ 10⁻¹⁰⁰.

^cThese genes are NOT present in the set of MT or RE homologues identified at e-value ≤ 10⁻¹⁰⁰.

N/A represents numbers that were not calculated.