How to distinguish linkage and crossover?

[maxpayne_lhp]

I really don't know how to distinguish beween 2 things, it's based on the ratio right?
Thanks

 

[iansmith]

A cross-over is the exchange of segments between two homologous chromosomes of linked genes/genetic loci.

Linkage is the association of gene or genetic loci and that will likely be transmitted together during recombination/cross over.

for example you have following genetic loci:

A B C D E F G H I
a b c d e f  g h i

gene C D E and F are linked

so during recombination gene/repeats are exchange as follow

a B  c d e f G h I
[B]A[/B] b [B]C D E F[/B] g [B]H[/B] i

So when you look at the phenotype/genotype you will always see that C D E and F are always together and have the same frequency, and that the frequency of A, B, G, H, and I is indepent of each other