Ig vs gamma globulin

Ig and gamma globulin both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ig	Yes	No	No	No
gamma globulin	Yes	No	No	No

As nouns, gamma globulin is a hypernym of Ig; that is, gamma globulin is a word with a broader meaning than Ig:

Ig: a class of proteins produced in lymph tissue in vertebrates and that function as antibodies in the immune response
gamma globulin: a plasma protein containing the immunoglobulins that are responsible for immune responses

Other hypernyms of Ig include human gamma globulin, antibody.

Ig (noun)	gamma globulin (noun)
a class of proteins produced in lymph tissue in vertebrates and that function as antibodies in the immune response	a plasma protein containing the immunoglobulins that are responsible for immune responses