Yes your inference is from the Sanghamitra paper and is apparently referring to y-haplogroup G2-P15. This association was picked up by somene on IC list. Iyer ancestry in Kerala, however, is much older than the Islamic invasions; probably they can be dated to the tamil sanskrit split. We must also factor in Sinhala origins.
Wikipedia on haplo G:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->Haplogroup G (Y-DNA)
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(Redirected from Haplogroup G (YDNA))
Jump to: navigation, search
In human genetics, Haplogroup G (M201) is a Y-chromosome haplogroup.
<b>Haplogroup G </b>has an overall low frequency in most populations but is widely distributed in Eurasia. It is most frequent in the Caucasus, and is also found in Asia Minor, the Middle East, the Balkans, Italy, with decreasing frequency in other parts of the world.
Little about its origins is currently known. It is a branch of haplogroup F* (M89), and is believed to <b>have originated in the Indus Valley between 10,000 and 20,000 years ago.</b><!--QuoteEnd--><!--QuoteEEnd-->
Oppenheimer gives G* origin in East Asia (p375). Probably we are dealing with a very ancient population originating in interior India-East Asia. which then expanded to the ME-anatolia-caucasus with the Kurds, iranians, but most likely indo-hittite or a precursor to hittite..... the hittite ending -os devolved into the familiar -os endings of greek.
from another source:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->http://www.isogg.org/tree/ISOGG_HapgrpG.htmlÂ
Haplogroup G has two primary sub-haplogroups, G1 and G2. By far, the most common sub-group in western Europe is G2. G1 occurs almost an order of magnitude less frequently than G2 in western Europe. A significant fraction of European G1âs are Ashkenazi Jews. Among Ashkenazi Jews, about 10% are in haplogroup G, including about 8% in G1 and 2% in G2. Haplogroups G3 and G5 have been reported for only single individuals from Turkey and Pakistan, respectively. G4 was mentioned in the article that announced G5, but has not yet been described.
<b>The founder of haplogroup G is thought to have lived about 30,000 years ago along the eastern edge of the Middle East, perhaps as far east as the Himalayan foothills in Pakistan or India. </b>A small number of haplogroup G people went eastward and on into Southeast Asia, south China and the Pacific Islands, but most spread over the Middle Eastern area and up into the Caucasus.<!--QuoteEnd--><!--QuoteEEnd-->
Judging from the Sanghamitra paper, it is also likely that Indian sampling for G is incomplete:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->http://www.jogg.info/21/Goff.pdf
The testing of one G2-P15 subject for DYF371 was
carried out to estimate whether or not the value of 14
on DYS425 was present from the beginning of
Haplogroup G2.<b> The subject was from a <i>tribal </i>area of
India and his G2 lineage has likely been separated from
the lineage that led to most European G2âs from the
earliest history of G2. </b>This subject was found to have
repeat values on DYF371 of 10c-12t-13c-13c, so the
DYS425 value (associated with the âTâ allele) was 12.
<b>Therefore, it appears that the two repeats were added in
a G2 individual at some early time after the founding of
G2. </b>Therefore, we would not normally expect to find
DYS425=14 in a member of G1 or G*, and this
conclusion is supported by the single example in Table 1
of a Haplogroup G1a individual, plus the single
example of a GxG2 individual reported to us in a
private communication.
...
The limited data for <b>GxG2 </b>suggests that the deletion
event in DYS452 occurred in a Haplogroup G2
individual or else was present in the founder of G2. <b>The
value of 27 on this marker for the G2 individual from a
tribal area of India supports the idea that the deletion
occurred in a person who was already G2, or that it
occurred very early in the history of G2. </b>Probably, the
deletion was present in the founder of G2, but has
become extinct outside G2, but this observation is based
on limited data.
<!--QuoteEnd--><!--QuoteEEnd-->
In India's huge population, original G indeed was dwarfed, while it was selected out in the caucasus hinterlands.
Wikipedia on haplo G:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->Haplogroup G (Y-DNA)
From Wikipedia, the free encyclopedia
(Redirected from Haplogroup G (YDNA))
Jump to: navigation, search
In human genetics, Haplogroup G (M201) is a Y-chromosome haplogroup.
<b>Haplogroup G </b>has an overall low frequency in most populations but is widely distributed in Eurasia. It is most frequent in the Caucasus, and is also found in Asia Minor, the Middle East, the Balkans, Italy, with decreasing frequency in other parts of the world.
Little about its origins is currently known. It is a branch of haplogroup F* (M89), and is believed to <b>have originated in the Indus Valley between 10,000 and 20,000 years ago.</b><!--QuoteEnd--><!--QuoteEEnd-->
Oppenheimer gives G* origin in East Asia (p375). Probably we are dealing with a very ancient population originating in interior India-East Asia. which then expanded to the ME-anatolia-caucasus with the Kurds, iranians, but most likely indo-hittite or a precursor to hittite..... the hittite ending -os devolved into the familiar -os endings of greek.
from another source:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->http://www.isogg.org/tree/ISOGG_HapgrpG.htmlÂ
Haplogroup G has two primary sub-haplogroups, G1 and G2. By far, the most common sub-group in western Europe is G2. G1 occurs almost an order of magnitude less frequently than G2 in western Europe. A significant fraction of European G1âs are Ashkenazi Jews. Among Ashkenazi Jews, about 10% are in haplogroup G, including about 8% in G1 and 2% in G2. Haplogroups G3 and G5 have been reported for only single individuals from Turkey and Pakistan, respectively. G4 was mentioned in the article that announced G5, but has not yet been described.
<b>The founder of haplogroup G is thought to have lived about 30,000 years ago along the eastern edge of the Middle East, perhaps as far east as the Himalayan foothills in Pakistan or India. </b>A small number of haplogroup G people went eastward and on into Southeast Asia, south China and the Pacific Islands, but most spread over the Middle Eastern area and up into the Caucasus.<!--QuoteEnd--><!--QuoteEEnd-->
Judging from the Sanghamitra paper, it is also likely that Indian sampling for G is incomplete:
<!--QuoteBegin-->QUOTE<!--QuoteEBegin-->http://www.jogg.info/21/Goff.pdf
The testing of one G2-P15 subject for DYF371 was
carried out to estimate whether or not the value of 14
on DYS425 was present from the beginning of
Haplogroup G2.<b> The subject was from a <i>tribal </i>area of
India and his G2 lineage has likely been separated from
the lineage that led to most European G2âs from the
earliest history of G2. </b>This subject was found to have
repeat values on DYF371 of 10c-12t-13c-13c, so the
DYS425 value (associated with the âTâ allele) was 12.
<b>Therefore, it appears that the two repeats were added in
a G2 individual at some early time after the founding of
G2. </b>Therefore, we would not normally expect to find
DYS425=14 in a member of G1 or G*, and this
conclusion is supported by the single example in Table 1
of a Haplogroup G1a individual, plus the single
example of a GxG2 individual reported to us in a
private communication.
...
The limited data for <b>GxG2 </b>suggests that the deletion
event in DYS452 occurred in a Haplogroup G2
individual or else was present in the founder of G2. <b>The
value of 27 on this marker for the G2 individual from a
tribal area of India supports the idea that the deletion
occurred in a person who was already G2, or that it
occurred very early in the history of G2. </b>Probably, the
deletion was present in the founder of G2, but has
become extinct outside G2, but this observation is based
on limited data.
<!--QuoteEnd--><!--QuoteEEnd-->
In India's huge population, original G indeed was dwarfed, while it was selected out in the caucasus hinterlands.