The means by which the development of the
differences between the sex is initiated
called sex determination. The actual development of primary and
secondary sexual characteristic is dependent upon hormonal cues, particularly
these from the gonad themselves.
1. XX Sex determination system
2. WZ Sex determination system
3. Autosomal Sex determination
4 .Multiple W Chromosome
5. Multiple X Chromosome
6. Multiple Y Chromosome
7. WXY System
8. XO System
9. ZO System
XX sex determination system:
Sex Chromosome in female are identical and
these in male are mismatched pair .Female are XX and male are XY. So,Female are
called homogametic and male are heterogametic. Heterogametic always determine
the sex of the progeny.The Y chromosome determine the sex .Example : Nile
Tilapia ( Oreochromis niloticus).
Fig: XX Sex Determination System
WZ sex determination system:
Sex chromosome in male are identical and
female are mismatched pair. Female are WZ and male are ZZ. Heterogametic female
determine the sex of fish.Example: Red Tilapia (Oreochromis aureus)
Fig: WZ Sex Determination System
Autosomal sex determination:
In this sex determination system,there is no
sex chromosome and sex is determined autosomally. Sex are determined by the
number of male or female genes that are located on the autosomes. Example:
Swordtail
Multiple W Chromosome:
Females are W1W2Z and males are ZZ. Females are heterogametic. Female determine the sex of offspring. Example: Virolito
Multiple X Chromosome:
Females are X1X1X2X2
and males are X1X2Y.
Females are homogametic and males are heterogametic. Heterogametic male
determine the sex of the offspring .Example: File fish
Males are XY1Y2 and Females are XX .
Heterogametic male determine the sex of the offspring . Example: Hoplias sp.
This is a variant on the XY sex determination system. The
W chromosome is a modified X chromosome .They can block the male determining ability
of the Y chromosome .So XY and YY fishes are male ,while XX, WX , WY fishes are
females. Both males and females can either homogametic or heterogametic.
Example:Platy fish
There is only one sex chromosome .The XO is a variant of
the XY system. Females are XX and male are XO (O is the symbol for no
chromosome).Heterogametic male determine the sex of the progeny. i.e; Those
receive X chromosome become female and those receive no sex chromosome become
males. Example: Dollar hatchet fish
ZO System
It is a
variant of WZ system. Here females are ZO and males are ZZ . Heterogametic
females determine the sex of the offspring.Example: Dworf gourami
2 Comments
Thanks a lot for your valuable time and efforts, Sir.
ReplyDeleteYou are most welcome !
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