G bandingG-banding, G banding or Giemsa banding is a technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. It is the most common chromosome banding method. It is useful for identifying genetic diseases (mainly chromosomal abnormalities) through the photographic representation of the entire chromosome complement. The metaphase chromosomes are treated with trypsin (to partially digest the chromosome) and stained with Giemsa stain.
Giemsa stainGiemsa stain (ˈgiːmzə), named after German chemist and bacteriologist Gustav Giemsa, is a nucleic acid stain used in cytogenetics and for the histopathological diagnosis of malaria and other parasites. It is specific for the phosphate groups of DNA and attaches itself to regions of DNA where there are high amounts of adenine-thymine bonding. Giemsa stain is used in Giemsa banding, commonly called G-banding, to stain chromosomes and often used to create a karyogram (chromosome map).
Deletion (genetics)In genetics, a deletion (also called gene deletion, deficiency, or deletion mutation) (sign: Δ) is a mutation (a genetic aberration) in which a part of a chromosome or a sequence of DNA is left out during DNA replication. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. Some chromosomes have fragile spots where breaks occur, which result in the deletion of a part of the chromosome. The breaks can be induced by heat, viruses, radiation, or chemical reactions.
CytogeneticsCytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping, analysis of G-banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH).
Locus (genetics)In genetics, a locus (: loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000. Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus.
Genetic variationGenetic variation is the difference in DNA among individuals or the differences between populations among the same species. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, but other mechanisms, such as genetic drift, contribute to it, as well. Genetic variation can be identified at many levels. Identifying genetic variation is possible from observations of phenotypic variation in either quantitative traits (traits that vary continuously and are coded for by many genes (e.
