Answer:
it happens when 2 organisms jelp each other beneficial.
Explanation:
eg:algae and leguminous plants.the algae live on the roots and take in the nitrogen from the soil,which the plant cannot do and needs for growth.it takes in the nitrogen and pases it to the roots and even make the soil loose for the roots to move and they get a living space(algae on the roots).
The DNA region is easily accessible
^^^^^^^^^^^^
