How to Use the Applet for Calculating an m Value from Tetrad Data


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About this site

This site was prepared by Dan Graham and Frank Stahl, Institute of Molecular Biology, University of Oregon, with the help of Russ Lande, University of California, San Diego.

Computerized calculations are based on the equations of Stahl and Lande, 1995 Estimating interference and linkage map distance from two-factor tetrad data, Genetics 139: 1449-1454.

How to use this site

1. Enter the total number of tetrads and the numbers of Tetratypes (T) and Nonparental ditypes (NPD) in the indicated boxes. (Or enter the numbers of NPD's, T's and PD's, and let the program calculate the Total.) Specify whether you want confidence intervals of 0.95 or of 0.99.

2. Click on "GO". An ellipse corresponding to the specified confidence interval will appear around a dot, whose coordinates correspond to the observed frequencies of T and NPD. The ellipse will intersect curves for m values that are acceptable at the designated level of confidence. These curves will turn blue, and the corresponding m values in the list will turn blue.

3. In addition, the 95% confidence interval for X (the counting model map distance in Morgans) is given for each m value that is acceptable at the designated degree of confidence (page 1451, right column).


You will need to do a print screen in order to make a hard copy of the applet. On a Macintosh this works best by following these steps

1. Enter you data into the boxes, and have it generate the m value graph.

2. Type Command(the 4-looped pattern button)+Shift+4. Note the plus signs mean hold the keys down together.

3. Your cursor will now be a cross-bar. Select the area of the screen that you wish to print by holding down the mouse and boxing in the portion of the graphic you wish to save. It will make a camera clicking sound and save the area you selected as a Picture# file to your startup drive.

4. Find the file on your drive and open it. This file can be printed, and the graphic will appear in the printout. It can also be ported into other programs.