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In genetics, imprinting is the suppressing (or silencing) of certain genes on chromosomes, depending on which parent they were received from.
When DNA is passed to daughter cells after fertilization of an egg by a sperm, certain alleles can become active only if they were received from the mother, others only if they came from the father. If a gene is suppressed through imprinting from one parent, and the allele from the other parent is not expressed because of mutation, neither can act and the child will be deficient. A healthy child cannot be produced when both sets of chromosomes come from the same parent. Imprinting of the same areas will occur and all these genes will be suppressed.
A process known as reprogramming occurs in the parent female or male when the egg or sperm is maturing. In many instances this is achieved through methylation of the DNA of genes or regulatory sequences, which results in the gene not being expressed. In other instances, phosphorylation or other chemical modification of histone proteins appears to lead to silencing.
Imprinting is known to cause problems in cloning, with clones having DNA that is not methylated in the right places. Some scientists think this is due to there not being enough time for reprogramming to be properly achieved. When a nucleus is added to an egg during somatic cell nuclear transferIn genetics, somatic cell nuclear transfer is a technique for cloning. What happens The nucleus of a cell contains the DNA of an organism, which acts as its blueprint. By removing the nucleus of a cell and replacing it with a nucleus from another cell, th, the egg starts dividing in minutes, as compared to the days or months it takes for reprogramming during embryonictadpole) of the wrinkled frog Rana rugosa . An embryo is an animal or a plant in its earliest stage of development. Plants In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl , and root (see rad development. If time is the responsible factor, it may be possible to delay cell division in clones, giving time for proper reprogramming to occur.
Several genetic diseasesA genetic disorder or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. There are a number of possible causes for genetic defects: They may be caused by an unwelcome mutation, as are most cancers. There ar that map to 15q13 (locus 3 of section 1 of the long arm of chromosome 15) in humans are due to abnormal imprinting. The Prader-Willi syndromePrader-Willi syndrome is a genetic disorder in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed ( chromosome 15q partial deletion). It was identified in 1956 by Andrea Prader, Heinrich Willi, Alexis Labhart, and Guido genes are expressed only when inherited from the father; the Angelman syndromeAngelman syndrome (AS) is neurological disorder in which severe learning difficulties are associated with a characteristic facial appearance and behavior. History Dr. Harry Angelman, a pediatrician working in Warrington, Cheshire, first reported three chi gene is expressed only when inherited from the mother. Thus, someone who inherits both chromosomes 15 from one parent (called uniparental disomyHumans ordinarily have two of each pair of chromosomes. This normal condition is termed disomy and ordinarily one chromosome will come from the mother and one from the father. If two consecutive abnormalities of reproduction occur, someone may inherit two) has Prader-Willi or Angelman syndrome, depending on which parent they come from.
A gene in sheepThis article is about the animal; for other meanings of Sheep see Sheep (disambiguation). A sheep is any of several woolly ruminant quadrupeds, but most commonly the Domestic Sheep Ovis aries , which probably descends from the wild urial of south-central called "callipyge" produces large buttocks consisting of muscle with very little fat. This gene is expressed only if it is on chromosome 18 inherited from the father and is not on the chromosome from the mother.
Molecular geneticsMolecular genetics is the field of biology which studies the structure and function of genes at a molecular level. Molecular genetics employs the methods of genetics and molecular biology. It is so-called to differentiate it from other sub fields of genet Gene expression Epigenetics| Politics | Business | Finance |
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