[ Pobierz całość w formacie PDF ]
another by single microsatellite mutations. Furthermore, these three
most common types were either completely absent or else barely
present in the Sorbs and Belarusians. The case for Slavic origins of
Ashkenazi Levites was showing some serious cracks.
When we started the Levite study, we intended to address the
simple question of whether the Mishnah was correct: has paternally
defined Levite status been faithfully transmitted as was observed for
Cohen status? Our data say no and provide a negative control for the
results of the Cohanim studies: we can fi nd no convincing genetic
signature of a high level of patrilineal inheritance among the broad
community of self-identified Levites their Y chromosome comple-
ment is much more heterogeneous than that of the Cohanim. Thus,
the genetic evidence appears to favor the suppositions of John Bright
(A History of Israel ) and Risto Nurmela (The Levites) that it was much
easier to become a Levite than it was a Cohen. To become a Cohen
69
looki ng out for number two
usually required a father who was a Cohen. To become a Levite
probably required no more than faith and conviction (and perhaps
the occasional well-placed bribe). Hence, we see all manner of Y
chromosomes among Levites.
But our work also led to a new question involving the one Y-
chromosome signature we did identify in great numbers, R-M17. Since
R-M17 is not common among current Jewish groups or, presumably,
among the ancient Hebrews, how did it come to be in such high
frequency in the Ashkenazi Levites?
One possibility is that there was never an influx of R-M17 chromo-
somes into the Levites from a Slavic or genetically similar source in
the fi rst place. Rather, the elevated R-M17 frequencies in Ashkenazi
Levites may be due to chance, or so-called genetic drift. Genetic drift
is the consequence of small population sizes. The gene forms that one
generation passes on to the next generation are not all the gene forms
(or variants) that generation has. Some individuals reproduce, others
don t; some reproduce more, some less. If the gene variant in question
has no effect on survival or reproduction, whether it is passed on is a
matter of chance. When population sizes are small this can result in
large changes in the proportions of gene forms from one generation to
the next. Because every gene form is equally likely to be passed on or
not when there is no selection on it, the phenomenon of genetic drift
can be likened to coin tossing. If you toss a fair coin ten times, the likeli-
hood of a large departure from the expected 50 percent heads is very
high. You could easily get something very different, such as only 30
percent heads. But if you toss it ten thousand times, the odds of such
a radical departure from expectation are very small. The same is true in
population genetics. When the population is small, large changes in the
frequency of types of genes can occur by chance, leading to extreme
increases or decreases in the frequencies of particular types. In the
case of the Levites, the relevant population size may have been small
enough to result in chance changes in haplotype composition.7
70
looki ng out for number two
Genetic drift therefore must be considered as a possible explanation
for the apparently foreign chromosome type common among the
Levites. While this is a formal possibility, it seems unlikely to me. If
the Levites were isolated from other Jews in their paternal heritage,
we would expect to see overall strong differences such as in the Co-
hanim. Or if drift occurred in the broader Jewish community, then
R-M17 should be in other Jews as well. But what we see is R-M17 at
high frequency only among the Ashkenazi Levites.
Our data suggest that the R-M17 chromosomes appeared among
the Ashkenazi Levites approximately a thousand years ago. Histori-
cally, such a date would appear to coincide with the consolidation and
expansion of the Ashkenazi community. If the R-M17 chromosomes
did not originate with the Sorbs or the Belarusians ancestors, where
did they come from? Is there another candidate population with a
putative Jewish connection? [ Pobierz całość w formacie PDF ]
zanotowane.pl doc.pisz.pl pdf.pisz.pl ocenkijessi.opx.pl
another by single microsatellite mutations. Furthermore, these three
most common types were either completely absent or else barely
present in the Sorbs and Belarusians. The case for Slavic origins of
Ashkenazi Levites was showing some serious cracks.
When we started the Levite study, we intended to address the
simple question of whether the Mishnah was correct: has paternally
defined Levite status been faithfully transmitted as was observed for
Cohen status? Our data say no and provide a negative control for the
results of the Cohanim studies: we can fi nd no convincing genetic
signature of a high level of patrilineal inheritance among the broad
community of self-identified Levites their Y chromosome comple-
ment is much more heterogeneous than that of the Cohanim. Thus,
the genetic evidence appears to favor the suppositions of John Bright
(A History of Israel ) and Risto Nurmela (The Levites) that it was much
easier to become a Levite than it was a Cohen. To become a Cohen
69
looki ng out for number two
usually required a father who was a Cohen. To become a Levite
probably required no more than faith and conviction (and perhaps
the occasional well-placed bribe). Hence, we see all manner of Y
chromosomes among Levites.
But our work also led to a new question involving the one Y-
chromosome signature we did identify in great numbers, R-M17. Since
R-M17 is not common among current Jewish groups or, presumably,
among the ancient Hebrews, how did it come to be in such high
frequency in the Ashkenazi Levites?
One possibility is that there was never an influx of R-M17 chromo-
somes into the Levites from a Slavic or genetically similar source in
the fi rst place. Rather, the elevated R-M17 frequencies in Ashkenazi
Levites may be due to chance, or so-called genetic drift. Genetic drift
is the consequence of small population sizes. The gene forms that one
generation passes on to the next generation are not all the gene forms
(or variants) that generation has. Some individuals reproduce, others
don t; some reproduce more, some less. If the gene variant in question
has no effect on survival or reproduction, whether it is passed on is a
matter of chance. When population sizes are small this can result in
large changes in the proportions of gene forms from one generation to
the next. Because every gene form is equally likely to be passed on or
not when there is no selection on it, the phenomenon of genetic drift
can be likened to coin tossing. If you toss a fair coin ten times, the likeli-
hood of a large departure from the expected 50 percent heads is very
high. You could easily get something very different, such as only 30
percent heads. But if you toss it ten thousand times, the odds of such
a radical departure from expectation are very small. The same is true in
population genetics. When the population is small, large changes in the
frequency of types of genes can occur by chance, leading to extreme
increases or decreases in the frequencies of particular types. In the
case of the Levites, the relevant population size may have been small
enough to result in chance changes in haplotype composition.7
70
looki ng out for number two
Genetic drift therefore must be considered as a possible explanation
for the apparently foreign chromosome type common among the
Levites. While this is a formal possibility, it seems unlikely to me. If
the Levites were isolated from other Jews in their paternal heritage,
we would expect to see overall strong differences such as in the Co-
hanim. Or if drift occurred in the broader Jewish community, then
R-M17 should be in other Jews as well. But what we see is R-M17 at
high frequency only among the Ashkenazi Levites.
Our data suggest that the R-M17 chromosomes appeared among
the Ashkenazi Levites approximately a thousand years ago. Histori-
cally, such a date would appear to coincide with the consolidation and
expansion of the Ashkenazi community. If the R-M17 chromosomes
did not originate with the Sorbs or the Belarusians ancestors, where
did they come from? Is there another candidate population with a
putative Jewish connection? [ Pobierz całość w formacie PDF ]