Replacement of a gene by a mutant version of the same gene using homologous recombination.


Inactivation of a gene by homologous recombination following transfection with a suitable DNA construct.

Major Histocompatibility Complex (MHC)

A large genomic region or family of genes in most vertebrates, which contains several genes with important functions for the immune system.

Monozygotic twin

Identical twins that are the result of a single zygote (fertilized egg) splitting into two cell masses and becoming two individuals. The twins are genetically identical and are always of the same sex.

Nuclear transfer

The generation of a new animal nearly identical to another one by injection of the nucleus from a cell of the donor animal into an enucleated oocyte of the recipient.


The egg mother cell; it undergoes two meiotic divisions (oogenesis) to form the egg cell. The primary oocyte is before completion of the first meiotic division; the secondary oocyte is after completion of the first meiotic division.


The process of giving birth.

Pronuclear injection

The use of a fine needle to inject DNA into the nucleus of an unfertilized egg.

Senescent cells

Animal cells that have nearly reached the limit of lifespan (usually around 50 doublings) in cell culture and are beginning to show signs of impending death.


Transplantation of cells, tissues, or organs from one species to another.


A fertilized oocyte

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