linkage

n. In genetics, the occurrence of two or more genes on the same chromosome, which makes it more likely they will stay together in the next generation. When sex cells divide in half to form ova and sperm, there is a period called crossing over in which the inherited chromosomes from the father and mother split up and some cross over to form new genetic strands so that each sex cell has a somewhat random half of the genes from each parent. If genes are on the same chromosome, the chance they will be in the same half in the sex cells and so be passed on together to the new generation increases.