The Jukes-Cantor (JC)
The Jukes-Cantor (JC) model is a simple yet important model in molecular evolution, specifically for studying the evolution of nucleotide sequences over time. It assumes that all four nucleotides (A, C, G, T) mutate at the same rate, and that each nucleotide has an equal probability of mutating into any of the other three nucleotides.
Example of Jukes-Cantor Model of Sequence Evolution:
Let's say we have two DNA sequences from different organisms, and we want to use the Jukes-Cantor model to estimate the evolutionary distance (i.e., the number of substitutions per site) between them.
Step 1: Initial Sequences
Consider two sequences:
Sequence 1:
AGCTGAC
Sequence 2:
ATCTGGC
Step 2: Identify Differences
To calculate the evolutionary distance between these sequences, first identify the positions where the sequences differ. Here’s a comparison of the sequences:
| Position | Sequence 1 | Sequence 2 | Difference? |
|---|---|---|---|
| 1 | A | A | No |
| 2 | G | T | Yes |
| 3 | C | C | No |
| 4 | T | T | No |
| 5 | G | G | No |
| 6 | A | G | Yes |
| 7 | C | C | No |
From this comparison, we observe that there are 2 differences (positions 2 and 6).