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Evidence from nuclear sequences that invariable sites should be considered when sequence divergence is calculated
1Department of Genetics, University of Wisconsin-Madison.
Molecular Biology and Evolution
|May 1, 1989
Summary
Not all nucleotide positions are equally mutable. Analysis of globin gene sequences reveals complex substitution patterns, suggesting current divergence estimates may significantly underestimate true genetic change.
Area of Science:
- Molecular Evolution
- Genetics
- Bioinformatics
Background:
- Amino acid replacements indicate sequence variability is not uniform.
- Nucleotide level analysis in mitochondrial DNA also shows constraints on substitutions.
- Previous models assumed simpler substitution patterns.
Purpose of the Study:
- To investigate nucleotide substitution patterns in globin gene sequences.
- To identify invariable nucleotide positions and analyze transition/transversion rates.
- To evaluate the accuracy of current models for estimating genetic divergence.
Main Methods:
- Examined globin gene sequences from various organisms.
- Analyzed nucleotide substitutions, including transitions and transversions.
- Tested models accounting for invariable sites and differential substitution rates.
- Investigated the role of concomitantly variable nucleotides (covariotides).
Main Results:
- Nearly all datasets showed invariable nucleotide positions.
- Transition/transversion ratios were inconsistent and rarely 2:1.
- Standard models often failed to fit observed data, even with adjustments.
- A subset of data could be simulated by including covariotides with stochastic turnover.
- Underestimation of nucleotide substitutions by current methods could be substantial.
Conclusions:
- Globin gene sequences exhibit complex, heterogeneous substitution patterns.
- Current models may significantly underestimate genetic divergence.
- Examining multiple divergent orthologous genes is crucial for accurate evolutionary analysis.