Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals

Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucl...
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Autor*in:	Gaffney, Daniel J [verfasserIn] Keightley, Peter D

Format:	E-Artikel
Sprache:	Englisch

Erschienen:	2008

Schlagwörter:	Substitution Rate Nucleotide Substitution Rate Fourfold Degenerate Site Intronic Site Estimate Substitution Rate

Anmerkung:	© Gaffney and Keightley; licensee BioMed Central Ltd. 2008

Übergeordnetes Werk:	Enthalten in: BMC evolutionary biology - London : BioMed Central, 2001, 8(2008), 1 vom: 30. Sept.
Übergeordnetes Werk:	volume:8 ; year:2008 ; number:1 ; day:30 ; month:09

Links:	Volltext

DOI / URN:	10.1186/1471-2148-8-265

Katalog-ID:	SPR026960974

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520			\|a Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment.
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allfields	10.1186/1471-2148-8-265 doi (DE-627)SPR026960974 (SPR)1471-2148-8-265-e DE-627 ger DE-627 rakwb eng Gaffney, Daniel J verfasserin aut Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals 2008 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier © Gaffney and Keightley; licensee BioMed Central Ltd. 2008 Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213 Keightley, Peter D aut Enthalten in BMC evolutionary biology London : BioMed Central, 2001 8(2008), 1 vom: 30. Sept. (DE-627)32664489X (DE-600)2041493-6 1471-2148 nnns volume:8 year:2008 number:1 day:30 month:09 https://dx.doi.org/10.1186/1471-2148-8-265 kostenfrei Volltext GBV_USEFLAG_A SYSFLAG_A GBV_SPRINGER SSG-OLC-PHA GBV_ILN_20 GBV_ILN_22 GBV_ILN_23 GBV_ILN_24 GBV_ILN_31 GBV_ILN_39 GBV_ILN_40 GBV_ILN_60 GBV_ILN_62 GBV_ILN_63 GBV_ILN_65 GBV_ILN_69 GBV_ILN_70 GBV_ILN_73 GBV_ILN_74 GBV_ILN_95 GBV_ILN_105 GBV_ILN_110 GBV_ILN_151 GBV_ILN_161 GBV_ILN_170 GBV_ILN_206 GBV_ILN_213 GBV_ILN_230 GBV_ILN_285 GBV_ILN_293 GBV_ILN_602 GBV_ILN_702 GBV_ILN_2001 GBV_ILN_2003 GBV_ILN_2005 GBV_ILN_2006 GBV_ILN_2008 GBV_ILN_2009 GBV_ILN_2010 GBV_ILN_2011 GBV_ILN_2014 GBV_ILN_2015 GBV_ILN_2020 GBV_ILN_2021 GBV_ILN_2025 GBV_ILN_2031 GBV_ILN_2038 GBV_ILN_2044 GBV_ILN_2048 GBV_ILN_2050 GBV_ILN_2055 GBV_ILN_2056 GBV_ILN_2057 GBV_ILN_2061 GBV_ILN_2111 GBV_ILN_2113 GBV_ILN_2190 GBV_ILN_4012 GBV_ILN_4037 GBV_ILN_4112 GBV_ILN_4125 GBV_ILN_4126 GBV_ILN_4249 GBV_ILN_4305 GBV_ILN_4306 GBV_ILN_4307 GBV_ILN_4313 GBV_ILN_4322 GBV_ILN_4323 GBV_ILN_4324 GBV_ILN_4325 GBV_ILN_4338 GBV_ILN_4367 GBV_ILN_4700 AR 8 2008 1 30 09
spelling	10.1186/1471-2148-8-265 doi (DE-627)SPR026960974 (SPR)1471-2148-8-265-e DE-627 ger DE-627 rakwb eng Gaffney, Daniel J verfasserin aut Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals 2008 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier © Gaffney and Keightley; licensee BioMed Central Ltd. 2008 Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213 Keightley, Peter D aut Enthalten in BMC evolutionary biology London : BioMed Central, 2001 8(2008), 1 vom: 30. Sept. (DE-627)32664489X (DE-600)2041493-6 1471-2148 nnns volume:8 year:2008 number:1 day:30 month:09 https://dx.doi.org/10.1186/1471-2148-8-265 kostenfrei Volltext GBV_USEFLAG_A SYSFLAG_A GBV_SPRINGER SSG-OLC-PHA GBV_ILN_20 GBV_ILN_22 GBV_ILN_23 GBV_ILN_24 GBV_ILN_31 GBV_ILN_39 GBV_ILN_40 GBV_ILN_60 GBV_ILN_62 GBV_ILN_63 GBV_ILN_65 GBV_ILN_69 GBV_ILN_70 GBV_ILN_73 GBV_ILN_74 GBV_ILN_95 GBV_ILN_105 GBV_ILN_110 GBV_ILN_151 GBV_ILN_161 GBV_ILN_170 GBV_ILN_206 GBV_ILN_213 GBV_ILN_230 GBV_ILN_285 GBV_ILN_293 GBV_ILN_602 GBV_ILN_702 GBV_ILN_2001 GBV_ILN_2003 GBV_ILN_2005 GBV_ILN_2006 GBV_ILN_2008 GBV_ILN_2009 GBV_ILN_2010 GBV_ILN_2011 GBV_ILN_2014 GBV_ILN_2015 GBV_ILN_2020 GBV_ILN_2021 GBV_ILN_2025 GBV_ILN_2031 GBV_ILN_2038 GBV_ILN_2044 GBV_ILN_2048 GBV_ILN_2050 GBV_ILN_2055 GBV_ILN_2056 GBV_ILN_2057 GBV_ILN_2061 GBV_ILN_2111 GBV_ILN_2113 GBV_ILN_2190 GBV_ILN_4012 GBV_ILN_4037 GBV_ILN_4112 GBV_ILN_4125 GBV_ILN_4126 GBV_ILN_4249 GBV_ILN_4305 GBV_ILN_4306 GBV_ILN_4307 GBV_ILN_4313 GBV_ILN_4322 GBV_ILN_4323 GBV_ILN_4324 GBV_ILN_4325 GBV_ILN_4338 GBV_ILN_4367 GBV_ILN_4700 AR 8 2008 1 30 09
allfields_unstemmed	10.1186/1471-2148-8-265 doi (DE-627)SPR026960974 (SPR)1471-2148-8-265-e DE-627 ger DE-627 rakwb eng Gaffney, Daniel J verfasserin aut Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals 2008 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier © Gaffney and Keightley; licensee BioMed Central Ltd. 2008 Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213 Keightley, Peter D aut Enthalten in BMC evolutionary biology London : BioMed Central, 2001 8(2008), 1 vom: 30. Sept. (DE-627)32664489X (DE-600)2041493-6 1471-2148 nnns volume:8 year:2008 number:1 day:30 month:09 https://dx.doi.org/10.1186/1471-2148-8-265 kostenfrei Volltext GBV_USEFLAG_A SYSFLAG_A GBV_SPRINGER SSG-OLC-PHA GBV_ILN_20 GBV_ILN_22 GBV_ILN_23 GBV_ILN_24 GBV_ILN_31 GBV_ILN_39 GBV_ILN_40 GBV_ILN_60 GBV_ILN_62 GBV_ILN_63 GBV_ILN_65 GBV_ILN_69 GBV_ILN_70 GBV_ILN_73 GBV_ILN_74 GBV_ILN_95 GBV_ILN_105 GBV_ILN_110 GBV_ILN_151 GBV_ILN_161 GBV_ILN_170 GBV_ILN_206 GBV_ILN_213 GBV_ILN_230 GBV_ILN_285 GBV_ILN_293 GBV_ILN_602 GBV_ILN_702 GBV_ILN_2001 GBV_ILN_2003 GBV_ILN_2005 GBV_ILN_2006 GBV_ILN_2008 GBV_ILN_2009 GBV_ILN_2010 GBV_ILN_2011 GBV_ILN_2014 GBV_ILN_2015 GBV_ILN_2020 GBV_ILN_2021 GBV_ILN_2025 GBV_ILN_2031 GBV_ILN_2038 GBV_ILN_2044 GBV_ILN_2048 GBV_ILN_2050 GBV_ILN_2055 GBV_ILN_2056 GBV_ILN_2057 GBV_ILN_2061 GBV_ILN_2111 GBV_ILN_2113 GBV_ILN_2190 GBV_ILN_4012 GBV_ILN_4037 GBV_ILN_4112 GBV_ILN_4125 GBV_ILN_4126 GBV_ILN_4249 GBV_ILN_4305 GBV_ILN_4306 GBV_ILN_4307 GBV_ILN_4313 GBV_ILN_4322 GBV_ILN_4323 GBV_ILN_4324 GBV_ILN_4325 GBV_ILN_4338 GBV_ILN_4367 GBV_ILN_4700 AR 8 2008 1 30 09
allfieldsGer	10.1186/1471-2148-8-265 doi (DE-627)SPR026960974 (SPR)1471-2148-8-265-e DE-627 ger DE-627 rakwb eng Gaffney, Daniel J verfasserin aut Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals 2008 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier © Gaffney and Keightley; licensee BioMed Central Ltd. 2008 Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213 Keightley, Peter D aut Enthalten in BMC evolutionary biology London : BioMed Central, 2001 8(2008), 1 vom: 30. Sept. (DE-627)32664489X (DE-600)2041493-6 1471-2148 nnns volume:8 year:2008 number:1 day:30 month:09 https://dx.doi.org/10.1186/1471-2148-8-265 kostenfrei Volltext GBV_USEFLAG_A SYSFLAG_A GBV_SPRINGER SSG-OLC-PHA GBV_ILN_20 GBV_ILN_22 GBV_ILN_23 GBV_ILN_24 GBV_ILN_31 GBV_ILN_39 GBV_ILN_40 GBV_ILN_60 GBV_ILN_62 GBV_ILN_63 GBV_ILN_65 GBV_ILN_69 GBV_ILN_70 GBV_ILN_73 GBV_ILN_74 GBV_ILN_95 GBV_ILN_105 GBV_ILN_110 GBV_ILN_151 GBV_ILN_161 GBV_ILN_170 GBV_ILN_206 GBV_ILN_213 GBV_ILN_230 GBV_ILN_285 GBV_ILN_293 GBV_ILN_602 GBV_ILN_702 GBV_ILN_2001 GBV_ILN_2003 GBV_ILN_2005 GBV_ILN_2006 GBV_ILN_2008 GBV_ILN_2009 GBV_ILN_2010 GBV_ILN_2011 GBV_ILN_2014 GBV_ILN_2015 GBV_ILN_2020 GBV_ILN_2021 GBV_ILN_2025 GBV_ILN_2031 GBV_ILN_2038 GBV_ILN_2044 GBV_ILN_2048 GBV_ILN_2050 GBV_ILN_2055 GBV_ILN_2056 GBV_ILN_2057 GBV_ILN_2061 GBV_ILN_2111 GBV_ILN_2113 GBV_ILN_2190 GBV_ILN_4012 GBV_ILN_4037 GBV_ILN_4112 GBV_ILN_4125 GBV_ILN_4126 GBV_ILN_4249 GBV_ILN_4305 GBV_ILN_4306 GBV_ILN_4307 GBV_ILN_4313 GBV_ILN_4322 GBV_ILN_4323 GBV_ILN_4324 GBV_ILN_4325 GBV_ILN_4338 GBV_ILN_4367 GBV_ILN_4700 AR 8 2008 1 30 09
allfieldsSound	10.1186/1471-2148-8-265 doi (DE-627)SPR026960974 (SPR)1471-2148-8-265-e DE-627 ger DE-627 rakwb eng Gaffney, Daniel J verfasserin aut Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals 2008 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier © Gaffney and Keightley; licensee BioMed Central Ltd. 2008 Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213 Keightley, Peter D aut Enthalten in BMC evolutionary biology London : BioMed Central, 2001 8(2008), 1 vom: 30. Sept. (DE-627)32664489X (DE-600)2041493-6 1471-2148 nnns volume:8 year:2008 number:1 day:30 month:09 https://dx.doi.org/10.1186/1471-2148-8-265 kostenfrei Volltext GBV_USEFLAG_A SYSFLAG_A GBV_SPRINGER SSG-OLC-PHA GBV_ILN_20 GBV_ILN_22 GBV_ILN_23 GBV_ILN_24 GBV_ILN_31 GBV_ILN_39 GBV_ILN_40 GBV_ILN_60 GBV_ILN_62 GBV_ILN_63 GBV_ILN_65 GBV_ILN_69 GBV_ILN_70 GBV_ILN_73 GBV_ILN_74 GBV_ILN_95 GBV_ILN_105 GBV_ILN_110 GBV_ILN_151 GBV_ILN_161 GBV_ILN_170 GBV_ILN_206 GBV_ILN_213 GBV_ILN_230 GBV_ILN_285 GBV_ILN_293 GBV_ILN_602 GBV_ILN_702 GBV_ILN_2001 GBV_ILN_2003 GBV_ILN_2005 GBV_ILN_2006 GBV_ILN_2008 GBV_ILN_2009 GBV_ILN_2010 GBV_ILN_2011 GBV_ILN_2014 GBV_ILN_2015 GBV_ILN_2020 GBV_ILN_2021 GBV_ILN_2025 GBV_ILN_2031 GBV_ILN_2038 GBV_ILN_2044 GBV_ILN_2048 GBV_ILN_2050 GBV_ILN_2055 GBV_ILN_2056 GBV_ILN_2057 GBV_ILN_2061 GBV_ILN_2111 GBV_ILN_2113 GBV_ILN_2190 GBV_ILN_4012 GBV_ILN_4037 GBV_ILN_4112 GBV_ILN_4125 GBV_ILN_4126 GBV_ILN_4249 GBV_ILN_4305 GBV_ILN_4306 GBV_ILN_4307 GBV_ILN_4313 GBV_ILN_4322 GBV_ILN_4323 GBV_ILN_4324 GBV_ILN_4325 GBV_ILN_4338 GBV_ILN_4367 GBV_ILN_4700 AR 8 2008 1 30 09
language	English
source	Enthalten in BMC evolutionary biology 8(2008), 1 vom: 30. Sept. volume:8 year:2008 number:1 day:30 month:09
sourceStr	Enthalten in BMC evolutionary biology 8(2008), 1 vom: 30. Sept. volume:8 year:2008 number:1 day:30 month:09
format_phy_str_mv	Article
institution	findex.gbv.de
topic_facet	Substitution Rate Nucleotide Substitution Rate Fourfold Degenerate Site Intronic Site Estimate Substitution Rate
isfreeaccess_bool	true
container_title	BMC evolutionary biology
authorswithroles_txt_mv	Gaffney, Daniel J @@aut@@ Keightley, Peter D @@aut@@
publishDateDaySort_date	2008-09-30T00:00:00Z
hierarchy_top_id	32664489X
id	SPR026960974
language_de	englisch
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author	Gaffney, Daniel J
spellingShingle	Gaffney, Daniel J misc Substitution Rate misc Nucleotide Substitution Rate misc Fourfold Degenerate Site misc Intronic Site misc Estimate Substitution Rate Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals
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topic_title	Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals Substitution Rate (dpeaa)DE-He213 Nucleotide Substitution Rate (dpeaa)DE-He213 Fourfold Degenerate Site (dpeaa)DE-He213 Intronic Site (dpeaa)DE-He213 Estimate Substitution Rate (dpeaa)DE-He213
topic	misc Substitution Rate misc Nucleotide Substitution Rate misc Fourfold Degenerate Site misc Intronic Site misc Estimate Substitution Rate
topic_unstemmed	misc Substitution Rate misc Nucleotide Substitution Rate misc Fourfold Degenerate Site misc Intronic Site misc Estimate Substitution Rate
topic_browse	misc Substitution Rate misc Nucleotide Substitution Rate misc Fourfold Degenerate Site misc Intronic Site misc Estimate Substitution Rate
format_facet	Elektronische Aufsätze Aufsätze Elektronische Ressource
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title	Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals
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title_full	Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals
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author_browse	Gaffney, Daniel J Keightley, Peter D
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author-letter	Gaffney, Daniel J
doi_str_mv	10.1186/1471-2148-8-265
title_sort	effect of the assignment of ancestral cpg state on the estimation of nucleotide substitution rates in mammals
title_auth	Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals
abstract	Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. © Gaffney and Keightley; licensee BioMed Central Ltd. 2008
abstractGer	Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. © Gaffney and Keightley; licensee BioMed Central Ltd. 2008
abstract_unstemmed	Background Molecular evolutionary studies in mammals often estimate nucleotide substitution rates within and outside CpG dinucleotides separately. Frequently, in alignments of two sequences, the division of sites into CpG and non-CpG classes is based simply on the presence or absence of a CpG dinucleotide in either sequence, a procedure that we refer to as CpG/non-CpG assignment. Although it likely that this procedure is biased, it is generally assumed that the bias is negligible if species are very closely related. Results Using simulations of DNA sequence evolution we show that assignment of the ancestral CpG state based on the simple presence/absence of the CpG dinucleotide can seriously bias estimates of the substitution rate, because many true non-CpG changes are misassigned as CpG. Paradoxically, this bias is most severe between closely related species, because a minimum of two substitutions are required to misassign a true ancestral CpG site as non-CpG whereas only a single substitution is required to misassign a true ancestral non-CpG site as CpG in a two branch tree. We also show that CpG misassignment bias differentially affects fourfold degenerate and noncoding sites due to differences in base composition such that fourfold degenerate sites can appear to be evolving more slowly than noncoding sites. We demonstrate that the effects predicted by our simulations occur in a real evolutionary setting by comparing substitution rates estimated from human-chimp coding and intronic sequence using CpG/non-CpG assignment with estimates derived from a method that is largely free from bias. Conclusion Our study demonstrates that a common method of assigning sites into CpG and non CpG classes in pairwise alignments is seriously biased and recommends against the adoption of ad hoc methods of ancestral state assignment. © Gaffney and Keightley; licensee BioMed Central Ltd. 2008
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title_short	Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals
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Effect of the assignment of ancestral CpG state on the estimation of nucleotide substitution rates in mammals

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