The EJHG has a new paper on the Y-DNA and mtDNA of European Roma. The main text is behind a paywall, but the images and supplementary info are freely available here and here, respectively. Interesting quote:
In agreement with our results, no traces of [Roma-specific] haplogroups H-M52, H-M82, or I-P259 were found in an extensive data set of 3136 non-Roma Europeans typed at similar resolution (472 Germans, 96 Danish, 340 Belgians, 90 Dutch, 370 Czechs, 520 Polish, 221 individuals from the United Kingdom, and 1027 Italians, from the Genographic project database, unpublished data), supporting our power to define founder lineages using our data set. With the exception of Hungary, for the reasons mentioned above, the presence of founder lineages in host populations confirms limited male gene flow from Roma to host. In contrast, male gene flow from hosts to Roma is much more frequent, although variable, ranging between 17% in Romania and up to 46% in Hungary.
Martínez-Cruz et al., Origins, admixture and founder lineages in European Roma, European Journal of Human Genetics advance online publication, 16 September 2015; doi:10.1038/ejhg.2015.201