Inherent promoter bidirectionality facilitates maintenance of sequence integrity and transcription of parasitic DNA in mammalian genomes

Table 1 Survey of human domesticated genes^a

Repeat family	Repeat type	Number	Chimeric	Bidirectional	Bidirectional with CpG island
DNA transposons	Tigger	13	2	8	8
	PiggyBac	5	2	1	1
	THAP (P-element)	12	2	6	6
	HSMAR (mariner)	1	1	0	0
	Others	11	2	3	3
Retrotransposons	Paraneoplastic antigens	8	0	2	2
	Ty3/gypsy	8	0	2	2
	Others	3	1	1	1
Endogenous retroviruses	Syncytin	2	0	0	0
Total		63	10 (15.9%)	23 (36.5%)	23

^a For a more detailed survey of domesticated TEs in the human genome see Additional file 1

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