Evolutionary age of repetitive element subfamilies and sensitivity of DNA methylation to airborne pollutants

Table 2 Characteristics of the repetitive element subfamilies examined in the present study

Repetitive element		Evolutionary age (Mya) ^a	CpG density (CpG _o/e) ^b	Mean methylation (%) ^c
Family	Subfamily
	L1PA5	20.4	0.073	25.3
LINE-1	L1PA2	7.6	0.104	70.6
	L1Hs	5	0.155	79.5
	L1Ta	1.9	0.282	70.1
	Alu Sx	40	0.878	24.7
*Alu*	Alu Yb8	2.9	0.884	89.9
	Alu Yd6	2	0.95	89.9
	MLT1D	98.2	0.043	97.9
HERV	ERV1	24.4	0.074	24.5
	ERV9	15	0.439	52

^a Estimated time in ‘Million years ago’ (Mya) based on the time when the repetitive element subfamily appeared in the human genome.
^b Approximate ratio of the observed to the expected CpG content (CpGo/e) of the sequence. CpG observed/expected (CpGo/e). The ratio is calculated using the formula ((Num of CpG/(Num of C × Num of G)) × Total number of nucleotides in the sequence).
^c Mean methylation of all low-exposure control groups from Study 1, Study 2, and Study 3.

ISSN: 1743-8977