About Scythian, lot of material is available on internet.
About genetics here is a good article
http://www.eupedia.com/europe/Haplogroup_R1a_Y-DNA.shtml
This link also contains some history related to Indo-European, Scythian, etc and genetics is also updated(latest by Dec. 2012)
This tendency to gyrate towards blogs is remarkable when you can get the actual papers. Authored papers should be relied upon more than blogs.
Here is one such paper, regarding R1a (which is turning into somewhat of a legend over here):
http://www.nature.com/ejhg/journal/v18/n4/full/ejhg2009194a.html
From conclusion:
Although the R1a1a* frequency and diversity is highest among Indo-Aryan and Dravidian speakers, the subhaplogroup R1a1a7-M458 frequency peaks among Slavic and Finno-Ugric peoples. Although this distinction by geography is not directly informative about the internal divisions of these separate language families, it might bear some significance for assessing dispersal models that have been proposed to explain the spread of Indo-Aryan languages in South Asia as it would exclude any significant patrilineal gene flow from East Europe to Asia, at least since the mid-Holocene period.
My understanding was that R1a was already in Indian subcontinent prior to 10000 BP.
This is also an interesting read, especially with map on page 4:
http://www.wiik.fi/kalevi/Wiik_Haplogroup_R1a.pdf
For a more broad spread, this article is good too:
http://evolutsioon.ut.ee/publications/Kivisild2000.pdf
Abstract -
A recent African origin of modern humans, although still disputed, is supported now by a majority of genetic studies. To address the question when and where very early diversification(s) of modern humans outside of Africa occurred, we concentrated on the investigation of maternal and paternal lineages of the extant populations of India, southern China, Caucasus, Anatolia and Europe. Through the analyses of about 1000 mtDNA genomes and 400 Y chromosomesfrom various locations in India we reached the following conclusions, relevant to the peopling of Europe in particular and of the Old World in general. First, we found that the node of the phylogenetic tree of mtDNA, ancestral to more than 90 per cent of the present-day typically European maternal lineages, is present in India at a relatively highfrequency. Inferred coalescence time of this ancestral node is slightly above 50,000 BP. Second, we found that haplogroup U is the second most abundant mtDNA variety in India as it is in Europe. Summing up, we believe that there are now enough reasons not only to question a 'recent Indo-Aryan invasion' into India some 4000 BP, but alternatively to consider India as a part of the common gene pool ancestral to the diversity of human maternal lineages in Europe. Our results on Y-chromosomal diversity of various Indian populations support an early split between Indian and east of Indian paternal lineages, while on a surface, Indian (Sanskrit as well as Dravidic speakers) and European Y-chromosomal lineages are much closer than the corresponding mtDNA variants.