BACTERIAL ARTIFICIAL CHROMOSOME (BAC). A cloning vector derived from a single-copy F-plasmid of Escherichia coli that carries the F replication and partitioning systems that ensure low copy number and faithful segregation of plasmid DNA to daughter cells. Large genomic fragments can be cloned into such vectors and they are faithfully replicated, which makes BACs useful for constructing genomic libraries.
EPISTASIS When the phenotype caused by a mutation in one gene is masked or enhanced by a mutation in another gene.
HAPLOTYPE An alternative form of a group of genes, part of a chromosome or a gene complex. The term is applied to groups of genetic loci, whereas the term 'allele' refers to alternative forms of a single gene.
INBRED STRAIN A strain that is essentially homozygous at all genetic loci. In mice, such strains are produced by brother–sister mating for at least 12 sequential generations, or more if other breeding systems are used.
PENETRANCE The proportion of affected individuals among carriers of a particular genotype. If all individuals with a disease genotype show the disease phenotype, then the disease is said to be completely penetrant.
QUANTITATIVE TRAIT LOCI (QTLs). Loci segregating alleles that have substantial input to the overall phenotype of a trait that is under complex genetic control.
RNA INTERFERENCE (RNAi). A technique in which the expression of a gene is inhibited when a double-stranded complementary RNA is introduced into the organism.
YEAST ARTIFICIAL CHROMOSOME (YAC). A large genomic fragment of up to 1 Mb in size, containing a centromere, an origin of replication and telomere sequences, that can be cloned into autonomously replicating yeast vectors. The genomic DNA fragments are maintained and propagated in the yeast Saccharomyces cerevisiae as linear chromosomes.
