isogamy vs amphimixis

isogamy and amphimixis both are nouns.

Word	Noun	Adjective	Verb	Adverb
isogamy	Yes	No	No	No
amphimixis	Yes	No	No	No

As nouns, amphimixis is a hypernym of isogamy; that is, amphimixis is a word with a broader meaning than isogamy:

isogamy: (biology) reproduction by the union or fusion of gametes of the same size and structure
amphimixis: reproduction involving the union or fusion of a male and a female gamete

Other hypernyms of isogamy include sexual reproduction.

isogamy (noun)	amphimixis (noun)
(biology) reproduction by the union or fusion of gametes of the same size and structure	union of sperm and egg in sexual reproduction
	reproduction involving the union or fusion of a male and a female gamete