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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. When a chromosome breaks, if a part of it is deleted or lost, the missing piece of chromosome is referred to as a deletion or a deficiency. [2]
The remaining copy of the tumor suppressor gene can be inactivated by a point mutation or via other mechanisms, resulting in a loss of heterozygosity event, and leaving no tumor suppressor gene to protect the body. Loss of heterozygosity does not imply a homozygous state (which would require the presence of two identical alleles in the cell).
After Muller's classification of gene mutation, an isomorph was described as a silent point mutant with identical gene expression as the original allele. [4] [5] m/Df = m/Dp Therefore, with respect to the relationship between the original and mutated genes, one cannot talk about the effects of dominance and/or recessiveness. [4] [5] [6]
Neomorphic mutations are a part of the gain-of-function mutations and are characterized by the control of new protein product synthesis. The newly synthesized gene normally contains a novel gene expression or molecular function. The result of the neomorphic mutation is the gene where the mutation occurs has a complete change in function. [56]
In the laboratory, mutagenesis is a technique by which DNA mutations are deliberately engineered to produce mutant genes, proteins, or strains of organisms. Various constituents of a gene, such as its control elements and its gene product, may be mutated so that the function of a gene or protein can be examined in detail.
DiGeorge syndrome is caused by a heterozygous deletion of part of the long arm (q) of chromosome 22, region 1, band 1, sub-band 2 (22q11.2). Approximately 80-90% of patients have a deletion of 3 Mb and 8% have a deletion of 1.5Mb. [31] [32] The number of genes affected by the deletion has been cited as approximately 30 to 50.
The human genome is the total collection of genes in a human being contained in the human chromosome, composed of over three billion nucleotides. [2] In April 2003, the Human Genome Project was able to sequence all the DNA in the human genome, and to discover that the human genome was composed of around 20,000 protein coding genes.
Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques.