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Introduction to the Contig Comparator

Gap4 commands such as Find Internal Joins, Find Repeats, Check Assembly, and Find Read Pairs automatically transform the Contig Selector to produce the Contig Comparator. To produce this transformation a copy of the Contig Selector is added at right angles to the original window to create a two dimensional rectangular surface on which to display the results of comparing or checking contigs.

Each of the functions plots its results as diagonal lines of different colours. In general, if the plotted points are close to the main diagonal they represent results from pairs of contigs that are in the correct relative order. Lines parallel to the main diagonal represent contigs that are in the correct relative orientation to one another. Those perpendicular to the main diagonal show results for which one contig would need to be reversed before the pair could be joined. The manual contig dragging procedure can be used to change the relative positions of contigs. As the contigs are dragged the plotted results will automatically be moved to their corresponding new positions. This means that, in general, if users drag the contigs to move their plotted results close to the main diagonal they will simultaneously be putting their contigs into the correct relative positions.

This plot can simultaneously show the results of independent types of search, making it easy for users to see if different analyses produce corroborating evidence for the ordering of contigs. Indications that a reading may have been assembled in an incorrect position can also be seen - if for example a result from Check Assembly lies on the same horizontal or vertical projection as a result from Find Repeats, users can see the alternative position to place the doubtful reading.

The plotted results can be used to invoke a subset of commands by the use of pop-up menus. For example if the user clicks the right mouse button over a result from Find Internal Joins a menu containing Invoke Join Editor and Invoke Contig Editors will pop up. If the user selects Invoke Join Editor the Join Editor will be started with the two contigs aligned at the match position contained in the result. If required one of the contigs will be complemented to allow their alignment.

(Click for full size image)

A typical display from the Contig Comparator is shown above. It includes results for Find Internal Joins in black, Find Repeats in red, Check Assembly in green, and Find Read Pairs in blue. Notice that there are several internal joins, read pairs and repeats close to the main diagonal near the top left of the display. This indicates that the contigs represented in that area are likely to be in the correct positions relative to one another. In the middle of the bottom right quadrant there is a blue diagonal line perpendicular to the main diagonal. This indicates a pair of contigs that are in the wrong relative orientation. The crosshairs show the positions for a pair of contigs. The vertical line continues into the Contig Selector part of the display, and the position represented by the horizontal line is also duplicated there.

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This page is maintained by staden-package. Last generated on 22 October 2002.