TABLE 2.

Percentages of endogenous retroviruses integrated within TUs

Cell source	% in TUs of ERV groupa:				Ensembl TUs in genome (%)
	ERVK	ERVL	ERV	ERV1
Chicken	11.2***	19.0***	8.9***	NAb	32.0
Human	24.5***	19.2***	25.9***	21.6***	35.0
Mouse	20.4***	25.3***	20.0	20.0***	27.7
Rat	14.4**	17.0***	12.1	12.4***	20.4

^a**, 0.001 < P < 0.01; ***, P < 0.001 (chi-square test).

^bNA, not applicable.