Concept:The exchange of genetic material between homologous chromosomes during meiosis is called crossing over.
Explanation:During prophase I of meiosis, homologous chromosomes pair up closely to form a bivalent or tetrad.
At this stage, non-sister chromatids may break at corresponding points and exchange segments of DNA.
These points of attachment are known as chiasmata.
This exchange produces recombinant chromosomes with new combinations of genes.
Crossing over increases genetic variation in offspring.
The other options are different processes: back cross and test cross are breeding techniques, while mutation is a sudden change in the genetic material itself.
Answer:A. crossing over