sex chromosome vs XX

sex chromosome and XX both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex chromosome	Yes	No	No	No
XX	Yes	No	No	No

As nouns, XX is a hyponym of sex chromosome; that is, XX is a word with a more specific, narrower meaning than sex chromosome:

sex chromosome: (genetics) a chromosome that determines the sex of an individual
XX: (genetics) normal complement of sex chromosomes in a female

Other hyponyms of sex chromosome include X chromosome, XXX, XXY, XY, XYY, Y chromosome.

sex chromosome (noun)	XX (noun)
(genetics) a chromosome that determines the sex of an individual	(genetics) normal complement of sex chromosomes in a female
	the cardinal number that is the sum of nineteen and one