What is a beneficial association between the roots of a plant and a fungus?

Mycorrhiza

Explanation: Mycorrhiza is a symbiotic relationship between a plant and a fungi. Nearly 80 percent of all plants with root systems participate in this mutualistic relationship. In mycorrhiza, the fungus forms a haustoria that penetrates the cell walls of the plant's roots. The fungus absorbs all the nutrients from the roots as they are transported to the plant. In return, the fungus gives the plant necessary chemicals and minerals that it cannot properly reach on its own.

Explanation:

Mycorrhiza is a  type of symbiotic association that occurs between fungi and roots of the plant in which both are benefited.  Mycorrhiza has many important roles in soil chemistry, plant nutrition, and some other fields. Basically this association takes place between roots of plants and fungi in which fungi supply minerals from the soil and plants provide food and shelter to the fungi and thus both are benefited.    

small, big, or no change could occur in the phenotype. it could cause something as simple as a cats ears to curl backwards or something as frighting as death. it could also occur in the protien-coding area and have an effect on that but no effect on the amino acids. what has to occur is a changing in the hox gene or the control gene.