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Loss of heterozygosity

 

 
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Loss of heterozygosity (LOH) in a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 represents the loss of normal function of one allele of a gene in which the other allele was already inactivated. This term is mostly used in the context of oncogenesis; after an inactivating mutation in one allele of a tumor suppressor gene occurs in the parent's germline cell, it is passed on to the zygote resulting in an offspring that is heterozygous for that allele.






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Loss of heterozygosity (LOH) in a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 represents the loss of normal function of one allele of a gene in which the other allele was already inactivated. This term is mostly used in the context of oncogenesis; after an inactivating mutation in one allele of a tumor suppressor gene occurs in the parent's germline cell, it is passed on to the zygote resulting in an offspring that is heterozygous for that allele. In oncology, loss of heterozygosity occurs when the remaining functional allele in a somatic cell of the offspring becomes inactivated by mutation. This results in no normal tumor suppressor being produced and almost certainly results in tumorigenesis.

In cancer

It is a common occurrence in cancer
Cancer

Cancer is a class of diseases in which a group of cell display uncontrolled growth , invasion , and sometimes metastasis . These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize....
, where it indicates the absence of a functional tumor suppressor gene
Tumor suppressor gene

A tumor suppressor gene, or antioncogene is a gene that protects a cell from one step on the path to cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes....
 in the lost region. However, many people remain healthy with such a loss, because there still is one functional gene left on the other chromosome of the chromosome pair. However, the remaining copy of the tumor suppressor gene can be inactivated by a point mutation
Point mutation

A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA....
, leaving no tumor suppressor gene to protect the body.

Retinoblastoma

The classical example of such a loss of protecting genes is hereditary retinoblastoma
Retinoblastoma

Retinoblastoma is a rapidly developing cancer which develops in the cells of the retina, the light sensitive cells of the eye. In the developed world, Rb has one of the best cure rates of all childhood cancers , with more than nine out of every ten sufferers surviving into adulthood....
, in which one parent's contribution of the tumor suppressor Rb1
Retinoblastoma protein

The retinoblastoma protein is a tumor suppressor protein that is dysfunctional in many types of cancer. One highly studied function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide....
 is flawed. Although most cells will have a functional second copy, chance loss of heterozygosity events in individual cells almost invariably lead to the development of this retinal cancer in the young child.

Detection

Loss of heterozygosity can be identified in cancers by noting the presence of heterozygosity at a genetic locus
Locus (genetics)

In the fields of genetics and evolutionary computation, a locus is a fixed position on a chromosome such as the position of a genetic marker that may be occupied by one or more genes....
 in an organism's germline
Germline

In biology and genetics, the germline of a mature or morphogenesis individual is the line of germ cells that have genetic material that may be passed to a child....
 DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
, and the absence of heterozygosity at that locus in the cancer cells. This is often done using polymorphic
Polymorphism (biology)

Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species ? in other words, the occurrence of more than one form or morph....
 markers, such as microsatellites or single nucleotide polymorphisms, for which the two parents contributed different alleles.

See also

  • Microsatellite instability
    Microsatellite instability

    Microsatellites are repeated sequences of DNA. Although the length of these microsatellites is highly variable from person to person, each individual has microsatellites of a set length....
  • Tumor suppressor gene
    Tumor suppressor gene

    A tumor suppressor gene, or antioncogene is a gene that protects a cell from one step on the path to cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes....