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Mirabilis jalapa
Mirabilis jalapa
Carl Correns
Carl Correns

Non-Mendelian inheritance is a general term that refers to any pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws. Mirabilis jalapa (The four o'clock flower or marvel of Peru) is the most commonly grown ornamental species of Mirabilis, and is available Carl Erich Correns ( September 10, 1864 - February 14, 1933) was a German Botanist and Geneticist, who is notable These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent If the genotypes of both parents in a genetic cross are known, Mendel’s laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.

Although inheritance of traits in fungi, viruses, and bacteria are all non-Mendelian, the phrase "non-Mendelian inheritance" is usually only used to describe the exceptions which occur in eukaryotic reproduction. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex [1]

Non-Mendelian inheritance plays a role in several disease processes. [2][3]

Contents

Types

Extranuclear inheritance

Extranuclear inheritance (also known as cytoplasmic inheritance) is a form of non-Mendelian inheritance first discovered by Carl Correns in 1908. When most people think of DNA they think of it as stored in Chromosomes that replicate inside the nucleus When most people think of DNA they think of it as stored in Chromosomes that replicate inside the nucleus Carl Erich Correns ( September 10, 1864 - February 14, 1933) was a German Botanist and Geneticist, who is notable [4] While working with Mirabilis jalapa Correns observed that leaf color was dependent only on the genotype of the maternal parent. Mirabilis jalapa (The four o'clock flower or marvel of Peru) is the most commonly grown ornamental species of Mirabilis, and is available Based on this data, he determined that the trait was transmitted through a character present in the cytoplasm of the ovule. Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells Later research by Ruth Sager and others identified DNA present in chloroplasts as being responsible for the unusual inheritance pattern observed. Ruth Sager ( February 7, 1918 &ndash March 29, 1997) was an eminent American Geneticist. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Work on the poky strain of the mold Neurospora crassa begun by Mary and Hershel Mitchell[5] ultimately led to the discovery of genetic material in mitochondria as well. Neurospora crassa is a type of red bread mold of the phylum Ascomycota. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells.

According to the endosymbiont theory, mitochondria and chloroplasts were once free living organisms that were taken up by a eukaryotic cell. An endosymbiont is any Organism that lives within the body or cells of another organism i [6] Over time, mitochondria and chloroplasts formed a symbiotic relationship with their eukaryotic hosts. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek Although the transfer of a number of genes from these organelles to the nucleus prevents them from living independently, each still possesses genetic material in the form of double stranded DNA.

It is the transmission of this organellar DNA that is responsible for the phenomenon of extranuclear inheritance. In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed Both chloroplasts and mitochondria are present in the cytoplasm of maternal gametes only. Thus, the phenotype of traits linked to genes found in either chloroplasts or mitochondria are determined exclusively by the maternal parent. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties

In humans, mitochondrial diseases are a class of diseases, many of which affect the muscles and the eye. Mitochondrial diseases are a group of disorders relating to the mitochondria, the Organelles that are the "powerhouses" of the eukaryotic cells

Gene conversion

Gene conversion can be one of major forms of non-Mendelian inheritance. Gene conversion is an event in DNA Genetic recombination, which occurs at high frequencies during meiotic division but which also occurs in somatic cells Gene conversion is a reparation process in DNA recombination, by which a piece of DNA sequence information is transferred from one DNA helix (which remains unchanged) to another DNA helix, whose sequence is altered. This may occur as a mismatch repair between the strands of DNA which are derived from different parents. DNA mismatch repair is a system for recognising and repairing erroneous insertion deletion and mis-incorporation of bases that can arise during DNA replication and recombination Thus the mismatch repair can convert one allele into the other. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms This phenomenon can be detected through the offspring non-Mendelian ratios, and is frequently observed, e. g. , in fungal crosses. [7]

Infectious heredity

Another form of non-Mendelian inheritance is known as infectious heredity. Infectious particles such as viruses may infect host cells and continue to reside in the cytoplasm of these cells. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable If the presence of these particles results in an altered phenotype, then this phenotype may be subsequently transmitted to progeny. [8] Because this phenotype is dependent only on the presence of the invader in the host cell’s cytoplasm, inheritance will be determined only by the infected status of the maternal parent. This will result in a uniparental transmission of the trait, just as in extranuclear inheritance.

One of the most well studied examples of infectious heredity is the killer phenomenon exhibited in yeast. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Two double-stranded RNA viruses, designated L and M, are responsible for this phenotype. An RNA virus is a Virus that has RNA (ribonucleic acid as its Genetic material. [9] The L virus codes for the capsid proteins of both viruses, as well as an RNA polymerase. For the leaf bug see Miridae. A capsid is the protein shell of a virus. RNA polymerase ( RNAP or RNApol) is an Enzyme that produces RNA. Thus the M virus can only infect cells already harboring L virus particles. The M viral RNA encodes a toxin which is secreted from the host cell. A toxin ( Greek:, toxikon, lit (poison for use on arrows is a Poisonous substance produced by living cells or organisms that is active at very low It kills susceptible cells growing in close proximity to the host. The M viral RNA also renders the host cell immune to the lethal effects of the toxin. For a cell to be susceptible it must therefore be either uninfected, or harbor only the L virus.

The L and M viruses are not capable of exiting their host cell through conventional means. They can only transfer from cell to cell when their host undergoes mating. All progeny of a mating involving a doubly infected yeast cell will also be infected with the L and M viruses. Therefore, the killer phenotype will be passed down to all progeny.

Heritable traits that result from infection with foreign particles have also been identified in Drosophila. Drosophila is a Genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" Wild type flies normally full recover after being anesthetized with carbon dioxide. Certain lines of flies have been identified that die off after exposure to the compound. This carbon dioxide sensitivity is passed down from mothers to their progeny. This sensitivity is due to infection with Sigma virus, a rhabdovirus only capable of infecting Drosophila. Rhabdoviruses are Viruses belonging to the family Rhabdoviridae, which is in the order Mononegavirales. [10]

Although this process is usually associated with viruses, recent research has shown that the Wolbachia bacterium is also capable of inserting its genome into that of its host. [11][12]

Genomic imprinting

Genomic imprinting represents yet another example of non-Mendelian inheritance. Genomic imprinting is a genetic phenomenon by which certain Genes are expressed in a Parent -of-origin-specific manner Just as in conventional inheritance, genes for a given trait are passed down to progeny from both parents. However, these genes are epigenetically marked before transmission, altering their levels of expression. These imprints are created before gamete formation and are erased during the creation of germ line cells. Therefore, a new pattern of imprinting can be made with each generation.

Genes are imprinted differently depending on the parental origin of the chromosome that contains them. A chromosome is an organized structure of DNA and Protein that is found in cells. In mice, the insulin-like growth factor 2 gene undergoes imprinting. Insulin-like growth factor 2 ( IGF-2) is one of three protein Hormones that share structural similarity to Insulin. The protein encoded by this gene helps to regulate body size. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Mice that possess two functional copies of this gene are larger than those with two mutant copies. The size of mice that are heterozygous at this locus depends on the parent from which the wild type allele came. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms If the functional allele originated from the mother, the offspring will exhibit dwarfism, whereas a paternal allele will generate a normal sized mouse. Dwarfism ( is a medical condition in humans characterized by extreme small size This is because the maternal Igf2 gene is imprinted. Imprinting results in the inactivation of the Igf2 gene on the chromosome passed down by the mother. [13]

Imprints are formed due to the differential methylation of paternal and maternal alleles. Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. This results in differing expression between alleles from the two parents. Sites with significant methylation are associated with low levels of gene expression. Gene expression is the process by which inheritable information from a Gene, such as the DNA sequence, is made into a functional Gene product, such Higher gene expression is found at unmethylated sites. [14] In this mode of inheritance, phenotype is determined not only by the specific allele transmitted to the offspring, but also by the sex of the parent that transmitted it.

Mosaicism

Individuals who possess cells with genetic differences from the other cells in their body are termed mosaics. These differences can result from mutations that occur in different tissues and at different periods of development. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism If a mutation happens in the non-gamete forming tissues, it is characterized as somatic. "Somatic" redirects here for the musician known as Somatic see Hahn Rowe. Germline mutations occur in the egg or sperm cells and can be passed on to offspring. In Biology and Genetics, the germline of a mature or developing individual is the line (sequence of Germ cells that have genetic material that [15] Mutations that occur early on in development will affect a greater number of cells and can result in an individual that can be identified as a mosaic strictly based on phenotype.

Mosaicism also results from a phenomenon known as X-inactivation. In Medicine ( Genetics) a mosaic or mosaicism denotes the presence of two populations of cells with different Genotypes in one X-inactivation (also called lyonization) is a process by which one of the two copies of the X chromosome present in Female Mammals is inactivated All female mammals have two X chromosomes. The X chromosome is one of the two sex-determining Chromosomes in many animal species including mammals (the other is the Y chromosome) To prevent lethal gene dosage problems, one of these chromosomes is inactivated following fertilization. Gene dosage is the number of copies of a Gene present in a cell or nucleus. For soil improvement see Fertilization (soil. This process occurs randomly for all of the cells in the organism’s body. Because a given female’s two X chromosomes will almost certainly differ in their specific pattern of alleles, this will result in differing cell phenotypes depending on which chromosome is silenced. Calico cats, which are almost all female[16], demonstrate one of the most commonly observed manifestations of this process. Tortoiseshell describes a coat coloring found in Cats Cats of this colour are mottled with patches of red and black [17]

Trinucleotide repeat disorders

Trinucleotide repeat disorders also follow a non-Mendelian pattern of inheritance. These diseases are all caused by the expansion of microsatellite tandem repeats consisting of a stretch of three nucleotides. Microsatellites, or Simple Sequence Repeats (SSRs are polymorphic loci present in nuclear and organellar DNA that consist of repeating Tandem repeats occur in DNA a pattern of two or more nucleotides is repeated and the repetitions are directly adjacent to each other Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group [18] In normal individuals, the number of repeated units is relatively low. With each successive generation, there is a chance that the number of repeats will expand. As this occurs, progeny can progress to permutation and ultimately affected status. Individuals with a number of repeats that falls in the permutation range have a good chance of having affected children. Those who progress to affected status will exhibit symptoms of their particular disease. Prominent trinucleotide repeat disorders include Fragile X syndrome and Huntington's disease. Fragile X syndrome, or Martin-Bell syndrome, is a genetic Syndrome which results in a spectrum (from none to severe of characteristic physical intellectual emotional Huntington's disease, also called Huntington's chorea, chorea major, or HD, is a genetic neurological disorder characterized after In the case of Fragile X syndrome it is thought that the symptoms result from the increased methylation and accompanying reduced expression of the fragile X mental retardation gene in individuals with a sufficient number of repeats. [19]

See also

References

  1. ^ Chapter 3. Gene Product Interaction and Nonmendelian. In Biology, the term epigenetics refers to changes in Gene expression caused by mechanisms other than changes in the underlying DNA sequence The Selfish gene theory postulates that Natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication. Retrieved on 2007-10-16. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 456 - Magister militum Ricimer defeats the Emperor Avitus at Piacenza and becomes master of the western
  2. ^ Van Heyningen V, Yeyati PL (2004). "Mechanisms of non-Mendelian inheritance in genetic disease". Hum. Mol. Genet. 13 Spec No 2: R225–33. doi:10.1093/hmg/ddh254. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15358729.  
  3. ^ Badano JL, Katsanis N (2002). "Beyond Mendel: an evolving view of human genetic disease transmission". Nat. Rev. Genet. 3 (10): 779–89. doi:10.1038/nrg910. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 12360236.  
  4. ^ Klug, William S. ; Michael R. Cummings, Charlotte A. Spencer (2006). Concepts of Genetics. Upper Saddle River, NJ: Pearson Education Inc. , 215.  
  5. ^ Mitchell MB, Mitchell HK (1952). "A Case of "Maternal" Inheritance in Neurospora Crassa". Proc. Natl. Acad. Sci. U. S. A. 38 (5): 442–9. doi:10.1073/pnas.38.5.442. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16589122.  
  6. ^ Embley, T. Martin; William Martin (March 2006). "Eukaryotic evolution, changes and challenges". Nature 430 (7084): 623-630. doi:10.1038/nature04546. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  7. ^ Stacey K. A. (1994). Recombination. In: Kendrew John, Lawrence Eleanor (eds. ). The Encyclopedia of Molecular Biology. Oxford: Blackwell Science, 945–950.
  8. ^ Klug, William S. ; Michael R. Cummings, Charlotte A. Spencer (2006). Concepts of Genetics. Upper Saddle River, NJ: Pearson Education Inc. , 223.  
  9. ^ Russell, Peter J. (2006). iGenetics: A Mendelian Approach. San Francisco: Pearson Education, Inc. , 649-650.  
  10. ^ Teninges, Danielle; Francoise Bras-Herreng (July 1987). "Rhabdovirus Sigma, the Hereditary CO2 Sensitivity Agent of Drosophila:Nucleotide Sequence of a cDNA Clone Encoding the Glycoprotein". Journal of General Virology 68: 2625-2638.  
  11. ^ University of Rochester Press Releases. Retrieved on 2007-10-16. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 456 - Magister militum Ricimer defeats the Emperor Avitus at Piacenza and becomes master of the western
  12. ^ Hotopp JC, Clark ME, Oliveira DC, et al (2007). "Widespread lateral gene transfer from intracellular bacteria to multicellular eukaryotes". Science 317 (5845): 1753–6. doi:10.1126/science.1142490. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 17761848.  
  13. ^ Bell, A. C. ; G. Felsenfeld (2000). "Methylation of a CTCF-dependent boundar control imprinted expression of the Igf2 gene". Nature 405: 482-485. doi:10.1038/35013100. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  14. ^ Lewin, Benjamin (2004). Genes VIII. Upper Saddle River, NJ: Pearson Education Inc. , 680-684.  
  15. ^ Lesson 3: Mosaicism. Retrieved on 2007-10-16. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 456 - Magister militum Ricimer defeats the Emperor Avitus at Piacenza and becomes master of the western
  16. ^ Genetics of Calico Color accessdate=.
  17. ^ Genetic Mosaicism. Retrieved on 2007-10-28. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 306 - Maxentius is proclaimed Roman Emperor. 312 - Battle of Milvian Bridge: Constantine
  18. ^ Lesson 1: Triplet Repeat Expansion. Retrieved on 2007-10-16. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 456 - Magister militum Ricimer defeats the Emperor Avitus at Piacenza and becomes master of the western
  19. ^ FMR1-Related Disorders. Retrieved on 2007-10-29. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 437 - Valentinian III, Western Roman Emperor, marries Licinia Eudoxia, daughter of his cousin Theodosius II

Further reading

External links

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