LOGO1

Introduction1

Triploids2

Tetraploids3

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Androgens5

Overview

Gynogens

Conclusion6

Introduction

Biotechnological manipulation of eggs, sperm or zygote by temperature,

pressure or chemical shocks either to alter chromosome set number or to create

fish only a single parent. This is done to crate haploid(n),triploid(3n) or

tetraploid(4n) and to create gynogens or androgens. It occurs through the or

subtraction of haploid set of chromosome present in the second polar body of the

egg by applying some sort of stimuli- heat, cold or pressure shock to the egg at

post fertilization stage.

Triploids:

The triploids are created for two reasons; increased growth rate and sterility.

Triploid are created by shocking newly fertilized eggs shortly after fertilization.

Fish eggs do not extrude the second polar body until they are fertilized. Because

of this if a newly fertilized egg is shocked, this shocks prevents the second polar

body from leaving the eggs. Consequently the fertilized egg will contain three

haploid nuclei; one from the egg, one from the sperm, and one from the second

polar body. The three haploid nuclei will fuse to form a triploid zygote nucleus

creating a triploid.

Fig: Process of triploid formation

Egg nucleus

sperm

Egg

2𝑛𝑑 polar body

shock

Triploids:

Triploidy can also be produced by crossing between a triploid & diploid. Such

tetraploid parent would produce diploid gametes and diploid will produce a haploid

gamete. In the cross a triploid can readily be produced.

This approach is attractive, as it does not require applying potentially damaging

treatment (heat, cold or pressure shock).

LOGOFig: The production of interploid-triploids

Triploids:

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Tetraploids

Tetraploid have four sets of chromosomes instead

of two. They can be created by shocking a diploid

zygote when it is undergoing first cleavage.

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Method of Tetraploid

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Gynogens

In gynogenesis the eggs are fertilized most

often with irradiated sperm. Such sperm can

only initiate the process of fertilization but no

gametic or nuclear exchange takes place.

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Gynogenesis

12Fig: Production of meiotic & mitotic gynogen

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Androgenesis

The androgens are opposite to gynogens. The

most commonly used method is to fertilize eggs

whose genetic material has been destroyed by

Gamma or X- ray with normal sperm. This

produces haploid androgen. When the haploid

androgenic zygote undergo first cleavage, it is

shocked to prevent cell division, and the two

haploids (N) nuclei fuse to form a diploid (2N)

nucleus.

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Androgenesis

14Fig: Induction of Androgenesis

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Conclusion

Manipulation of chromosome is technically

feasible & it is easy for fish. Although reports

on the induction of polyploidy was made on

aquatic animals in 1940s. the practical

appeal of its production and application in

fish started in 1970s and since then the

literature on the line has been staggering.

So this process should be more developed.

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Prepared by

Md. Masudur Rahman

B.Sc. In Fisheries(Hons.)

Patuakhali Science and Technology University

Contact: masudranapstu@gmail.com

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