- Synonymous substitution : 주어진 Codon에서 Neucleotide가 바뀌어도 Amino acid 종류가 바뀌지 않음 (아미노산을 변형시키지 않는 염기 돌연변이, Time-dependent)
- Nonsynonymous substitution: 주어진 codon에서 neucleotide가 바뀌면 Amino acid 종류 바뀜 (아미노산을 변형시키는 염기 돌연변이, Selection-dependent)
- ds : nonsynonymous substitution / nonsynonymous site
- ds : synonymous substitution / synonymous site
- dn/ds < 1 → Negative selection (기존 상태 유지하려 함, 진화 속도 느림)
- This suggest that the DNA sequence is under negative or purifying selection
- Negative selection is selection that limit change in a corresponding amino acid sequence
- This occurs when some aspect of the structure and/or function of a protein is critical and cannot tolerate substitutions
- dn/ds >1 → Positive selection (기존 상태 벗어나려 함, 진화 속도 빠름)
- An example of positive selection is with a duplicated gene that is under pressure to evolve new functions
- dn/ds = 1 → Neutral selection (중립적)
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