How do birds and dogs both use dna as instructions for building their bodies even though they are very different organisms

DNA is the genetic material in mostly all the forms of life present on the earth. It contains all the information about the genotype and appearance of any organism.  

Both birds and dogs use DNA as instructions for building their bodies even though they are very different organisms because DNA of all the organism are made up of same four type of base adenine, thymine, cytosine, and guanine.

These bases make genetic code that is universal in all the organisms. So if a genetic code AUG codes for methionine in dog then in bird also it will code for methionine. This proves that all the organisms are linked with each other and it is called unity in diversity.