Transgenic Animals

 INTRODUCTION
Livestock Animals are a major source of food, milk, wool, leather & many other byproducts. Naturally has always been an interest in improving the efficiency of livestock production. Until recently selective breeding was the only way to enhance genetic features of animals. however, this method is time consuming & can introduce limited variation. New gene transfer techniques & introduction of cloned genes into fertilized eggs, successful implantation of modified eggs into receptive female & getting progeny carrying cloned gene has resulted into development of new area of transgenic animals. Transgenic animal is a fertile animal that carries an introduced gene(s) in its germ line

TRANSGENIC MICE
The aim of transgenesis is to produce animals with beneficial traits. There are many difficulties faced in achieving success in fish and farm animals, however, with mouse the transgenesis experiments are not the one to yield any production but are meant for experimental purpose. Transgenic mice serves as a model for transgenic experiments. ability to produce a transgenic mice has opened new approach to studying fundamental problems of development & disease in mammals.

Mouse is appropriate choice because they have short generation time, super ovulated mouse can yield up to 40 eggs, reimplantation is relatively easy & mouse can carry up to 20 offspring.

PRODUCTION OF TRANSGENIC MOUSE
Mouse is a model system used for introduction of genes & expression of genes stably. external genes or targeted mutagen of mouse gene are introduced in germ line of fertile animals. This results in production of either Chimera of mosaics. Mice with all tissues made up of introduced DNA or transgene are chimera. Mosaics are animals carrying introduced DNA in some & not all tissues. They may have DNA from some other source also. Frequency of transgene depends on extent to which the manipulated cells have contributed to germ cells. chimeras or mosaics if have transgene in germ cells will pass it to offspring by mendelian law.

Established routes of transgenesis of mice are:
   1. Microinjection of DNA into pronucleus of fertilized egg,
   2. Retroviral infection of fertilized egg at 4-8 cell stage,
   3. Genetic alterations of embryonic stem cells & their introduction into blastocyst,
   4. Retroviral infection of embryo after implantation into uterus