blastocyst embryo	A day 3.5 embryo with 64-128 cells comprised of essentially two cell types: trophectoderm cells contributing to extra-embryonic membranes/tissues and inner cell mass cells (ICM) that lead to the embryo proper. In the mouse, these embryos characteristically have a diamond ring-shape appearance with a hollowed-out cavity (blastocoel) as a consequence of hydrostatic pressure generated by the trophectoderm cells
cDNA clone	Double stranded DNA copy of a messenger RNA (mRNA) encoding a specific gene
conditional and/or inducible knockouts	Mice generated by the genetic manipulation of embryonic stem (ES) cells such that a specific genetic locus has been altered by the addition of recombinase recognition elements flanking the gene sequence, or region of importance, to facilitate its deletion from the genome (i.e., the generation of a null allele) in the cells of one or more defined lineages
congenic strain of mice	Strains of mice that are genetically identical except for a limited genetic region or locus. For instance, a homozygous strain of mouse can be said to be congenic to another strain of mice at a particular locus following 12 or more successive backcrosses to this new strain. Selection of offspring based on specific genetic markers at each successive generation can speed this process such that a congenic strain of mice is produced in as little as 5 backcross generations
DNA methylation	The chemical modification of genomic DNA occurring in many eukaryotes (particularly mammals) in which methyl (CH3) groups are added to cytosine bases as a mechanism of inducing heritable changes in gene function without a change in DNA sequence (i.e., epigenetic changes). Generally, methylation is usually associated with turning-off (i.e., silencing) gene expression
Embryonic Stem cell (ES cell)	A pluripotent undifferentiated cell derived from the inner cell mass (ICM) of a blastocyst embryo that can give rise to cells comprising any embryonic lineage, and therefore any tissue/organ, with the exception of the extra-embryonic lineages of the developing fetus
exon-intron splicing motifs	Sequence elements in nuclear RNA representing the boundaries of gene segments that will be included (exons) or excluded (introns) during RNA processing and the production of mature mRNAs exported to the cytoplasm for translation into protein
expression cassette	A DNA construct that contains the necessary transcriptional (i.e., promoter) and RNA processing motifs (i.e., exon-intron splicing and poly(A) addition recognition sites) to allow expression of a protein encoding sequence in a transgenic mouse
gain of function mutation	A genetic mutation that confers new and/or enhanced activity(ies) to a given gene
genome	The total genetic information contained within a single set of chromosomes (eukaryotes) or in the heritably transferred genetic information associated with bacteria, phages, or eukaryotic DNA/RNA viruses
germ line	The lineage of embryonic and/or adult cells devoted to the production of eggs (female) or sperm (male) needed for sexual reproduction
hypomorph	Engineered mouse that has reduced levels of gene expression relative to the level of expression observed in a wild type mouse
indel	Genetic mutation leading to a co-localized insertion/deletion resulting in the net gain or loss in nucleotides. A microindel is similarily defined as an indel that results in the net gain or loss of 1 to 50 nucleotides
Knockin (KI) Mice	Mice generated by the genetic manipulation of embryonic stem (ES) cells such that a specific genetic locus has been altered either by the one-forone substitution of DNA sequence information or by the addition of sequence information not found in the endogenous genetic locus
Knockout (KO) Mice	Mice generated by the genetic manipulation of embryonic stem (ES) cells such that a specific genetic locus is targeted and rendered non-functional either by the insertion of irrelevant DNA sequence information to disrupt the expression of the encoding locus or by the deletion of DNA sequence information from the targeted locus
loss of function (i.e., null) mutation	A genetic mutation that results in either the complete loss (null) or greatly diminished activity(ies) of a given gene
metazoan	Any of the animals belonging to the subkingdom Metazoa, having a body made up of differentiated cells arranged in tissues and organs. All multicellular animals besides sponges are metazoans
orthologue	A gene in different organisms that have diveraged as a consequence of speciation and not DNA gene duplication (i.e., paralogue) paralogue A gene in different organisms that have diveraged as a consequence of DNA gene duplication and not speciation (i.e., orthologue)
poly(A)-addition signal sequence	Genomic DNA sequence motif that promotes cleavage of the primary nuclear RNA transcript and the subsequent extra-genomic addition of adenine (A)-containing nucleotides to this cleaved RNA
promoter	cis-acting DNA sequence of a gene that independently (i.e., even when removed from the protein encoding DNA sequences of that gene) is able to “promote” gene expression through the binding of available transcription factors
pronuclei	The haploid nuclei of a sperm and egg present prior to fusion and the formation of the single nucleus of the zygote (i.e., single-cell stage of embryonic development including the time between fertilization and prior to the initial cleavage into a two cell-stage embryo)
pseudopregnant-recipient females	A female mouse following copulation with a vasectomized (or sterile) male in which many of the characteristics of pregnancy are present (without an accompanying fetus), allowing the introduction and subsequent implanation of embryos following adoptive transfer into the reproductive tract
sequence complexity	The total length of unique (i.e., diverse non-repetitive) sequence information in a given population or genome
SNPs	Single Nucleotide Polymorphism(s) - unique nucleotide change(s) in a DNA sequence associated with a given gene or genetic locus that have the potential to change and/or modify gene expression
Systems Biology	A gestalt view of life science which attempts to define the functional aspects of a cell and/or organism through studies of interactions between the individual components of a given biological system
transgene	The gene(s) and/or DNA sequence information integrated into the genome following introduction into an embryo usually, but not exclusively, by physically introducing the DNA by microinjection
transgenic mice	Strains of mice generated by the introduction of exogenous genes or DNA sequences (transgenes) which typically integrate as a single chromosomal insertion event that becomes a heritable Mendelian trait
vector and/or plasmid sequences	The DNA sequence elements (usually of prokaryotic origin) that allow the propagation and production of the genes and/or DNA sequences of interest in preparation for transgenic mouse production
xenograft	A surgical graft of cells, tissues, and/or organs from an animal species of one genus to an animal species of another genus