Answer:
The correct option is a) the relative distance between the genes.
Step-by-step explanation:
A short distance between genes is a very little target for crossing-over to occur, which means that only a few of them will happen, compared with the number of events between genes that are more separated between each other.
Two genes that are very close have a few recombination events and are strongly bounded. These genes are linked.
The percentage of recombination frequency (P = Recombinant number / Total of individuals) is useful to determine the genetic distance between two or more genes. This distance results from multiplying that frequency by 100 and expressing it in map units (MU) or centiMorgans (cM). One centiMorgan (cM) equals one map unit (MU).
The map unit or centiMorgan is the distance between the pair of genes for which every 100 meiotic products only one results in a recombinant product.