Table 1. Allele and genotype frequencies for the DRD4 variable number tandem repeat polymorphism (n=340).

Allele/genotype	Number	Frequency (%)
Allele
2	79	11.6
3	46	6.7
4	408	60.0
5	14	2.0
6	3	< 1
7	124	18.2
8	6	< 1
Total	680
Genotype
2/2	12	3.5
2/3	8	2.3
2/4	31	9.1
2/5	1	<1
2/6	1	<1
2/7*	13	3.8
2/8*	1	<1
3/4	25	7.3
3/5	6	1.8
3/6	1	<1
3/7*	4	1.2
3/8*	2	< 1
4/4	133	39.1
4/5	7	2.0
4/6	1	<1
4/7*	77	22.6
4/8*	1	<1
7/7*	14	4.1
Genotype classification
Short (< 7 repeats)	228	67.1
Long (≥ 7 repeats)	112	32.9
Total	340	100.0

^*These genotypes were classified as long (high risk); all remaining genotypes were classified as short (low risk).