No, that is wrong. Ethnicity has nothing to do with DNA, similarities in outer appearance, kinship or blood relationship. It is even dangerous to attribute people with characteristics which are grounded in natural explanations. E.g. it is natural for a man to beat up his wife, it's in his genes and hormones. This is wrong because the majority of men doesn't beat up their wives, among other reasons it is rather a certain image of masculinity which they try to resemble and which makes violence more acceptable for men than for women. Even though there are criminals with a Roma background, not all Roma people are criminal and stealing is not rooted in their genes. Such an image is a social construction which is called "naturalisation" (=to explain social things with nature). If you don’t know what a Roma is, click here