Biology Hour____ Name_________________________________________
Dr. Wexler
Two-Point Linkage Mapping
3/10/09
Due 3/11/09

A series of 2-point test crosses (double heterozygote vs. double homozygous recessive) were carried out among seven genes.

For example CcDd x ccdd. If the first parent produces gametes CD, cd, Cd, and cD in equal proportion, then the genes are either on different chromosomes or far apart on the same chromosome and therefore in different “linkage groups”. If two gamete genotypes are more abundant than the other two than the more abundant ones are the parental types and the less abundant ones are the recombinant types. In this case the genes are close to each other on the same chromosome (reducing the chance of crossing over between them), and are therefore in the same linkage group.

Instructions:

1. Using the recombination frequencies as a guide, divide the seven genes into linkage groups:

   A. How many linkage groups are there? ______

   B. What genes are in each linkage group?

2. Next, determine the order of the genes within each linkage group showing the distances between neighboring genes. Draw the maps proportional to distance.

The data is as follows:

Testcross     Recombination frequency           (%) Testcross     Recombination frequency (%)

c and d        50                                           m and r              50

c and m       50                                           m and t              50

c and r         11                                           m and v             19

c and t         29                                           m and z              50

c and v        50                                            r and t               40

c and z        39                                            r and v               50

d and m      29                                            r and z                28

d and r        50                                            t and v               50

d and t        50                                            t and z                50

d and v       10                                            v and z                50

d and z       50