Genetic linkage ,Mapping & crossing over

crossing over is the exchange of segment between homologous chromosomes

 

just as in diagram it is represented that fragment x has homologous chromosome

that is cr,Band other Y has ++.when it is cross over it then produce parental genotype

and as well as recombinant that is cr + and +B.they are cross over

EVIDENCES OF CROSS-OVER

Direct evidence was firstly given in  1931 by c.stern working on drosophila

stern studied two x chromosomes that differed from the normal x chromosomes.that one chromosome has y chromosome on its one end and 2nd ha smaller than normal chromosomes.

Two linked gene eye color( car) and shape is bar like and cross over occur in these just as in diagram on top.

Gene mapping