Explain why the value of the recombination frequency between any two genes is limited to 50%.

During meiosis, each chromosome has 2 chromatids. When homologous chromosomes pair they form a tetrad (2 chromosomes, 4 chromatids).

Crossing over can happen between 2 out of the 4 chromatids, and as a result, only half of the resulting gametes (at most) can be recombinant. The other 2 gametes will be parental.