Why was it necessary to complete the gram stain in order to determine the bacterial species infecting anna?

Gram negative and Gram positive refers to if bacteria retain the Gram Stain or not. Gram positive do. Gram negative do not. Gram positive bacteria will appear purple/blueish after staining. It is important because whether a bacteria is Gram positive or negative helps determine the species, characteristics of disease, and the best antibiotics to use in treatment. 

Crossing over creates new combinations of genes in the gametes that are not found in either parent contributing to genetic diversity