An edge is a direct connection between two nodes in a graph. It is often represented as a line, either straight or curved. The meaning of an edge depends on the context. For instance, in a phylogenetic tree, an edge typically indicates direct descent, but if two edges end in a node, they may also represent reticulation events such as horizontal gene transfer or contamination. An edge may be either undirected or directed. In the latter case, the direction is often shown by drawing the line as an arrow.
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