Types of Linkage and its significance:
Linkages are primarily of two types: Complete and incomplete.
Complete Linkage: When the combined characters occurs together in a regular manner in more than two generations, it is known as a complete linkage. Because of this complete linkage, only two types of gametes are formed. Example: Drosophila melanogaster
In Drosophila, the genes of grey body(G) and long wings(L) are dominant over black body(g) and vestigial wings(l). If pure breeding grey bodied long winged Drosophila (GL) are crossed with black bodied vestigial winged Drosophila (gl), in F2 generation a 3 : 1 ratio of parental phenotypes occurs (3 is for grey body long winged and one is for black body vestigial winged).
In the incomplete linkage, where new gene combinations are formed in the progeny or offsprings. This occurs due to the formation of a chiasma or crossing over between the linked genes.
Morgan and his students have found that linked genes show varied recombinations, some being more tightly linked than others,In Drosophila.
- Because of the linkage between genes, desired characters cannot be brought together by breeders. If the genes would sort independently then this would be possible only.
- There is no chance of recombination of the linked genes because the characters are remains linked .