Thank you for the opportunity to help you with your question!
Crossing over is the mutual
exchange of corresponding segments of non-sister chromatids of
homologous chromosomes at the pachytene substage of meiosis I to produce
new genetic recombinations.
Because of crossing over only, recombinations can occur.
The exchange of segments between the non-sister chromatids of two
homologues is so exact that neither of the two gains or loses any gene.
If they do not undergo crossing over, then no recombination will take
place and so, much of the parental traits will be seen in the offsprings
called as 'Linkage'.
Please let me know if you need any clarification. I'm always happy to answer your questions.