### Theory:

$$XX-XO$$ type:
Males have only one sex chromosome in this type of sex determination. Males are heterogametic, which means that some sperms carry the $$X$$ chromosome while others do not. Females are homogametic $$XX$$. Eggs fertilised by sperms with an $$X$$ chromosome become females, while eggs fertilised by sperms without an $$X$$ chromosome become males. Female is thus ($$2A$$ + $$XX$$) and male is ($$2A$$ + $$XO$$).

Some insects like grasshoppers, cockroaches and roundworms have the $$XX$$-$$XO$$ type of sex determination system.
Heredity of sex chromosomes in XO sex determination
$$ZW$$-$$ZZ$$ type:
In this type of sex determination, females are heterogametic, producing two types of gametes ($$Z$$ and $$W$$), whereas males are homogametic, producing only one type of gametes  ($$ZZ$$). This type of sex determination can be observed in birds as well as some reptiles.

Sex determination in birds
$$Z0$$-$$ZZ$$ type:
Females have an odd sex chromosome ($$AA$$+$$Z$$) in the $$ZO$$-$$ZZ$$ type of sex determination, whereas males have two homomorphic sex chromosomes ($$AA$$ + $$ZZ$$).  This type of sex determination can be observed in butterflies and moths.

Sex determination in butterfly
Important!
Do you know!
Organisms like wasps and bees have no sex chromosomes.
Reference: