Heterogametic Male:Because of two types of gametes produced by male it is called Heterogametic male.
Heterogamtic males are of two types:
(i): XX-XY type- In man and other mammals, plants and many insects like Drosophila , etc the female has homogametic XX type while male has X and Y chromosome.The sex of the embryo depends on the type of the sperm or male gamete(X or Y type). If the female gamete is fertilised by “X” sperm the embryo will be carrying female sex , while if it is fertilised by “Y” sperm the embryo will be male.
(ii) XX-XO type:
In some insects like grasshopper, bugs, etc…..females are homogametic i.e XX type but the male has only one sex chromosome, i.e “X” only.The male has chromosome numbers les that that of female.The female will produce only one type of eggs(XX) but male produces 50%sperm with ‘X’ and other 50% without ‘X’. The sex of offspring depends on the sperms that
fertilises the egg.
In most of the species like birds, moths and some fish a chromosomal mechanism of sex determination occurs that is basically identical to the XX-XY type.
As the females are heterogametic it is designated as ZW. The males being homogametic it is designated as ZZ. This is referred to as ZZ-ZW type.
(i) ZO-ZZ type:
The female possesses single Z chromosome in moth, butterflies and domestic chickens. Female produces 2 types of eggs one with ‘Z’ chromosome and other without ‘Z’ chromosome. While the male produces only one type of sperm carrying ‘Z’ only. The sex is determined on the basis of egg type being fertilised.
(ii) ZW-ZZ type:
This type is common in insects, fish, reptiles, birds, etc…..Females are heterogametic with ZW type while males are homogametic with ZZ type. Female produces two types of eggs, i.e; 50% with ‘z’ and other 50% with ‘W’, while male produces only one type of sperm that is with ‘Z’. The sex of the offspring depends on the type of egg is fertilised.
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