| A | B |
|---|
| position effect | Used to describe a situation in which the phenotype expressed by a gene is altered by changes in the position of the gene within the genome. For instance genes translocated to regions of heterochromatin are often not expressed |
| Inversion | A chromosomal mutation involving the removal of a chromosome segment, its rotation through l80 degrees, and its reinsertion in the same location. The replacement of a section of a chromosome in the reverse orientation |
| duplication | More than one copy of a particular chromosomal segment in a chromosome set |
| Deletion | Loss of a DNA (chromosome) segment from a chromosome |
| deficiency | The absence of part of the normal genome or chromosome set |
| monosomy | An aberrant, aneuploid state in a normally diploid cell or organism in which one chromosome is missing, leaving one chromosome with no analog |
| trisomy | An aberrant, aneuploid state in a normally diploid cell or organism in which there are three copies of a particular chromosome instead of two copies |
| aneuploidy | The condition of a cell or of an organism that has additions or deletions of a small number of whole chromosomes from the expected balanced diploid number of chromosomes |
| allopolyploidy | polyploid produced by the hybridization of two species |
| autopolyploidy | A polyploid formed from the doubling of a single genome. Polyploidy in which all the chromosomes come from the same species |
| polyploidy | The condition of a cell or organism that has more than its normal number of sets of chromosomes |
| intercalating agents | A chemical that can insert itself between the stacked bases at the centre of the DNA double helix, possibly causing a frameshift mutation |
| base analogs | A chemical whose molecular structure mimics that of a DNA base; because of the mimicry, the analogue may act as a mutagen |
| Tautomers | Alternate chemical forms in which DNA (or RNA) bases are able to exist |
| mismatch base repairs | A form of excision repair initiated at the sites of mismatched bases in DNA |
| suppressor mutation | A mutation that counteracts the effects of another mutation. It maps at a different site than the mutation it counteracts, either within the same gene or at a more distant locus |
| true reversion | a point mutation form mutant back to wild type in which the change codes for the original amino aid of the wild type |
| reverse mutation | A mutational change from a mutant allele back to a wild-type allele |
| forward mutation | A mutation that converts a wild-type allele to a mutant allele |
| frameshift mutation | A mutation in which there is an addition or deletion of one, two or a small number (not a multiple of three) of nucleotides that causes the codon reading frame to shift to one of two others from the point of the mutation during translation |
| nonsense mutation | A gene mutation in which a base-pair change in the DNA causes a change I an mRNA codon from an amino acid-coding codon to a chain-terminating (nonsense) codon. As a result, polypeptide chain synthesis is terminated prematurely and the product is therefore either nonfunctional or, at best, partially functional |
| missense mutation | mutations that change a codon for one amino acid into a codon for a different amino acid |
| neutral mutation | A mutation that has no phenotypic effect |
| silent mutation | mutation in which the function of the protein product of the gene is unaltered |
| transversion | A mutation in which a purine/pyrimidine replaces a pyrimidine/purine base pair or vice versa eg. GC with TA |
| transition | A type of nucleotide-pair substitution involving the replacement of a purine with another purine, or of a pyrimidine with another pyrimidine for example GC with AT |
| base-pair mutation (point mutation) | A mutation that can be mapped to one specific site within a locus. A small mutation that consists of the replacement (transition or transversion); addition; or deletion (frameshift) of a base |
| teratogen | An agent that interferes with normal development |
| mutagen | An agent that is capable of increasing the mutation rate |
| induced mutation | mutations that occur as a result of treatment with known chemical or physical mutagens. |
| spontaneous mutation | A mutation occurring in the absence of mutagens, usually due to errors in the normal functioning of cellular enzymes |
| germ-line mutation | mutation occurring in cells that are destined to develop into gametes |
| homologous recombination | Breakage and reunion between homologous lengths of DNA |
| degenerate genetic code | A genetic code in which some amino acids may each be encoded by more than one codon |
| termination factors | The specific proteins in polypeptide synthesis(translation) that read the chain termination codons and then initiate a series of specific events to terminate polypeptide synthesis |
| initiation factors | Proteins required for the proper initiation of translation |
| translocation of ribosome | a part of the translation process in which the mRNA is shifted one codon in relation to the ribosome |
| peptidyl transferase | The enzymatic centre in the ribosome responsible for peptide bond formation during translation |
| Shine-Dalgarno sequence | In prokaryotes, a sequence to the 5’ side of an mRNA’s initiation codon which base pairs with the 3’ end of 16S rRNA in the small ribosomal subunit to allow the ribosome to locate the true initiator region of the mRNA. |
| P site | The site on the ribosome occupied by the peptidyl-tRNA just before peptide bond formation |
