The mechanism that breaks the linkage between linked genes is

Crossing over

Explanation:

Crossing over is the process during which two chromatids of two homologous chromosomes exchange part of their genetic segments. It occurs during the pachytene stage of prophase I of meiosis I.

Linked genes are mostly inherited together and do not exhibit independent assortment. However, when linked genes are present far apart from each other on the same chromosome, crossing over can occur between them to produce recombinant chromatids. Therefore, crossing over can break the linkage and produce recombinant progeny as it occurs during the independent assortment of unlinked genes.