In a series of crosses to look at the relationship of differ

In a series of crosses to look at the relationship of different genes with each other, the following crosses were performed. The numbers of offspring obtained from each cross are shown.

Cross                              offspring                                                      linkage?   

AaBb x aabb          20 AaBb, 15 Aabb, 18 aaBb, 17aabb

CcDd x ccdd          54 CcDd 49 ccdd, 98 Ccdd, 101 ccDd

EeFf x eeff        43 EeFf   7 Eeff 42 eeff   5 eeFf

a) For each one, note whether the genes are linked, and if so how closely (in mu); and whether the alleles are present in coupling or repulsion in the heterozygous parent.

b) Which genes are most tightly linked (closest together on the same chromosome)?  

Solution

Answer:

Cross                              offspring                                                      linkage?   

AaBb x aabb          20 AaBb, 15 Aabb, 18 aaBb, 17aabb No linkage as the test cross progeny are in 1:1:1:1 ratio.

CcDd x ccdd          54 CcDd 49 ccdd, 98 Ccdd, 101 ccDd Alleles are in repulsion. linkage is 34.1 mu. The alleles, Cd on one chromosome and cD alleles on their homologous chromsome are linked.

EeFf x eeff        43 EeFf 7 Eeff 42 eeff   5 eeFf Alleles are in coupling. Linkage is 12.37 mu. The alleles, ED on one chromosome and ed alleles on their homologous chromsome are linked.