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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:

PositionSequence 1Sequence 2Difference?
1AANo
2GTYes
3CCNo
4TTNo
5GGNo
6AGYes
7CCNo

From this comparison, we observe that there are 2 differences (positions 2 and 6).