测序质量分值简介
测序质量分值用来评估碱基的错误检出率。利用边合成边测序（SBS）技术，read中的每个碱基会得到基于phred样算法1,2与最初为桑格测序实验开发的算法类似）的质量分值。
测序技术视频
了解Illumina SBS如何工作。
Q值定义
指定碱基的测序质量分值Q是按照如下公式定义的：
Q = -10log10(e)
其中e是预估的碱基错误检出率。
- Q值高，说明错误率低。
- Q值低，可能会导致不可用read的比例显著增高。还可能导致假阳性变异检出率增加，得出不正确的结论。
如下所示，20的质量分值代表了错误率为1/100，对应的检出准确率为99%。
| 质量分值 | 碱基的错误检出率 | 推断的碱基检出精确度 |
|---|---|---|
| 10 (Q10) | 1/10 | 90% |
| 20 (Q20) | 1/100 | 99% |
| 30 (Q30) | 1/1000 | 99.9% |
Illumina测序质量分值
Illumina测序化学过程提供较高的精确度，绝大多数碱基得分在Q30及以上。这种精确度水平是多种测序应用的理想选择，包括临床研究。了解为何PhiX可以作为Illumina NGS运行中的质控品，进行运行质量监测。
Run Quality Monitoring
Learn what PhiX is and how it can be used as an in-run control for sequencing run quality monitoring in Illumina NGS.
Read BulletinBenefits of SBS Technology
Proven base-calling accuracy and uniform coverage enable robust base calling across the genome, giving you confidence in your results.
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参考文献
- Ewing B, Hillier L, Wendl MC, Green P. (1998): Base-calling of automated sequencer traces using phred. I. Accuracy assessment. Genome Res. 8(3):175-185
- Ewing B, Green P. (1998): Base-calling of automated sequencer traces using phred. II. Error probabilities. Genome Res. 8(3):186-194