Of the different sources of genetic variability, which one causes the variation in the combinations of homologs from paternal and maternal linage found within a haploid cell? (a) independent assortment(b) crossing over(c) random fertilization(d) mutation

Crossing over.

Explanation:

Crossing over may be defined as the phenomena of exchange of the genetic material between the non- sister chromatids of the homologous chromosomes. The crossing over occurs at the pachytene stage.

The crossing over may provide a source of genetic variation as it can create variation in the homologs of paternal and maternal lineage, present within a haploid cell. This crossing over occurs during the process of synapsis.