Conversely genes close to each other on the chromosome are usually tightly linked because the probability of a recombination event between them is very low. Consider a pair of chromosomes, and think about the gene loci at each ends. Now consider linkage. If the A and B loci were on the same chromosome, to determine the proportions of the four gametes we would have to know the probability of recombination between the two loci. For loci at opposite ends of long chromosomes, r can be very close to 0.5 because a recombination event is likely to occur.
Recombination can shuffle existing variation and lead to new variants.
Important to note that just as recombination can generate favorable combinations of alleles, recombination can just as easily break up these favorable combinations.