According to Mendel's second law of independent assortment, how are genes located on separate chromosomes inherited?

Mendel's second law of independent assortment states that the alleles of different genes assort independently of one another during gamete formation. This principle applies specifically to genes that are located on separate chromosomes or are far apart on the same chromosome. As a result, the inheritance of one gene does not influence the inheritance of another, allowing for a diverse combination of traits to be passed to the offspring.

In practical terms, when two genes are inherited independently, the combinations of traits can vary greatly, leading to a more varied genetic makeup in the progeny. This contrasts with genes that are linked (those located close together on the same chromosome), which tend to be inherited together more frequently due to their proximity.

The other options do not align with Mendel's findings. For instance, the idea of genes being inherited together as a unit applies to linked genes, not to those on separate chromosomes, while concepts like incomplete dominance and co-dominance refer to how alleles express themselves in the phenotype rather than their inheritance pattern. The understanding of independent assortment is fundamental to genetics and demonstrates the variability seen in offspring traits.