When chiasma frequency is 100%, the percentage of crossing over is

Answer: Option A

When chiasma frequency is 100%, the percentage of crossing over is 50%.
A chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids and is called a chromosomal crossover.
When chiasma is organized in between two gene loci, only 50% of meiotic products shall be crossovers and 50% non-crossovers. Thus, the chiasma frequency is twice the frequency of cross-over products, therefore, when the chiasma frequency is 100%, the percentage of crossing-over is halved i.e. 50%.