During meiosis (a type of cell division), homologous chromosomes exchange parts with each other. This leads to new combinations of genes on each chromosome.
Another way that recombination happens during meiosis. The chromosomes inherited from mom and dad randomly assort into gametes, leading to many possible combinations.
Genetic Linkage: Genes located close together on a chromosome tend to be inherited together because they are less likely to be separated by recombination.