共查询到20条相似文献,搜索用时 15 毫秒
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Mark A. Batzer Stephen T. Sherry Prescott L. Deininger Mark Stoneking 《Journal of molecular evolution》1997,45(1):3-6
Summary The posited universal cause of codon disappearance, extreme genomic % GC, is apparently not required for codon reassignment.
Rigorously interpreted, this does not eliminate codon disappearance as a contributor to reassignment, but it implies that
all reassignments are unlikely to be so caused. Even more significantly, the rationale for the axiom that reassigned codons must
first disappear has been eliminated. That is, it has been asserted that a codon with two meanings would be lethal (Osawa and
Jukes 1989). A complete inability to distinguish serine and leucine is of course lethal. However, a state of reduced ambiguity
in which CUG means both serine and leucine not only stably exists in wild-type organisms in which leucine-to-serine reassignment
has occurred, but such ambiguity may even have a favorable, rather than a lethal, phenotype.
The potential list of possible ambiguous intermediates has been expanded by the discovery of the multiple amino acid specificity
of Candida Ser- and Leu-tRNASer (Suzuki et al. 1997). Other means of making codons ambiguous, such as ribosomal ambiguity or unusual concentrations or sequences
of particular tRNAs, are easily envisioned. We look forward to further fossil ambiguous states and further elucidation of
their phenotypes. From such data we may ultimately be able to deduce the forces that occasionally drive modern codons from
one meaning to another. 相似文献
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Michael F. Hammer Doron M. Behar Tatiana M. Karafet Fernando L. Mendez Brian Hallmark Tamar Erez Lev A. Zhivotovsky Saharon Rosset Karl Skorecki 《Human genetics》2009,126(5):725-726
It has been known for over a decade that a majority of men who self report as members of the Jewish priesthood (Cohanim) carry
a characteristic Y chromosome haplotype termed the Cohen Modal Haplotype (CMH). The CMH has since been used to trace putative
Jewish ancestral origins of various populations. However, the limited number of binary and STR Y chromosome markers used previously
did not provide the phylogenetic resolution needed to infer the number of independent paternal lineages that are encompassed
within the Cohanim or their coalescence times. Accordingly, we have genotyped 75 binary markers and 12 Y-STRs in a sample
of 215 Cohanim from diverse Jewish communities, 1,575 Jewish men from across the range of the Jewish Diaspora, and 2,099 non-Jewish
men from the Near East, Europe, Central Asia, and India. While Cohanim from diverse backgrounds carry a total of 21 Y chromosome
haplogroups, 5 haplogroups account for 79.5% of Cohanim Y chromosomes. The most frequent Cohanim lineage (46.1%) is marked
by the recently reported P58 T->C mutation, which is prevalent in the Near East. Based on genotypes at 12 Y-STRs, we identify
an extended CMH on the J-P58* background that predominates in both Ashkenazi and non-Ashkenazi Cohanim and is remarkably absent
in non-Jews. The estimated divergence time of this lineage based on 17 STRs is 3,190 ± 1,090 years. Notably, the second most
frequent Cohanim lineage (J-M410*, 14.4%) contains an extended modal haplotype that is also limited to Ashkenazi and non-Ashkenazi
Cohanim and is estimated to be 4.2 ± 1.3 ky old. These results support the hypothesis of a common origin of the CMH in the
Near East well before the dispersion of the Jewish people into separate communities, and indicate that the majority of contemporary
Jewish priests descend from a limited number of paternal lineages. 相似文献
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