Why is reproductive isolation required for speciation to occur?

This is collection of data made by comparing objects in standard units. in science, the units are metric.

In cattle a single gene with two alleles determines fur color the fur can be red white or roan roan fur has both red and white hair which of the following statements is true a the allele for roan fur color is dominant over red and white fur color b the allele for red fur color is dominant over white and roan fur color c the roan and white alleles are expressed independently of the other d the red and white alleles are expressed independently of each other

How is synaptic signaling different from paracrine signaling?