True statement about transgenic mice -

Transgenic mice are generated by pronuclear injection of foreign DNA into fertilized mouse oocytes and subsequent transfer into the oviduct of pseudopregnant foster mothers. This process of generating transgenic animal would alter germ cell lines and be passed on to offsprings. So, the transgenic animals have the same genome as parents except for few (1 or more) genes that have been integrated or inactivated. This replacement of one gene in embryonic stem cell creates a heterozygous transgenic animals. The mating in 2 such animals will result in 25% homozygous offsprings. Careful breeding will establish a transgenic line in which all animals are homozygous for new genes.