Transgenesis - Many generations of selective mating are required to improve livestock and other domesticated animals genetically for traits such as milk yield, wool characteristics and rate of weight gain.

The selective mating procedure is time consuming and costly. Until recently, selective breeding was the only way to enhance the genetic features of domesticated animals. The process of gene manipulation to permanently modify the germ cells of animals is called as "Transgenesis".

The animal is called as "transgenic" animal. However, transgenic mice have been produced which carry genetic lesions identical to those existing in certain human inherited diseases. Such mice can be used as models for the development and evaluation of new pharmaceutical entities.

Production of these proteins is tightly regulated by promoters that limit genes to express only in cells of the mammary gland. The regulatory sequences from the genes of milk specific proteins have been cloned along with the gene of interest and used to control the expressions of genes in transgenic animals.

One of the goals of transgenesis of dairy cattle is to change the constituents of milk. The amount of cheese produced from milk is directly proportional to the K -casein content. Increasing K-casein production with an over-pressed K-casein transgenic is a reasonable likelihood. For a different end use, heterologous expression of a lactose transgene in the mammary gland could result in milk that is free of lactose.