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= = Academic publications ( incomplete ) = =
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" Fabrication of mercuric iodide radiation detectors " , Lodewijk van den Berg and Ron D. Vigil , Nuclear Instruments and Methods in Physics Research Section A : Accelerators , Spectrometers , Detectors and Associated Equipment , Volume 458 , Issues 1 @-@ 2 , 1 February 2001 , Pages 148 @-@ 151
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" Improved yield of high resolution mercuric iodide gamma @-@ ray spectrometers " , Vernon Gerrish and Lodewijk van den Berg , Nuclear Instruments and Methods in Physics Research Section A : Accelerators , Spectrometers , Detectors and Associated Equipment , Volume 299 , Issues 1 @-@ 3 , 20 December 1990 , Pages 41 @-... |
" Vapor growth of HgI2 by periodic source or crystal temperature oscillation " , by M. Schieber β , W.F. Schnepple , L. Van den Berg . Journal of Crystal Growth , Volume 33 , Issue 1 , April 1976 , Pages 125 β 135
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= Wrigley Square =
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Wrigley Square is a public square located in the northwest section of Millennium Park in the Historic Michigan Boulevard District of the Loop area of Chicago in Cook County , Illinois , United States . The square is located at the southeast corner of the intersection of East Randolph Street and North Michigan Avenue .... |
= = Detail = =
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Lying between Lake Michigan to the east and the Loop to the west , Grant Park has been Chicago 's front yard since the mid 19th century . Its northwest corner , north of Monroe Street and the Art Institute , east of Michigan Avenue , south of Randolph Street , and west of Columbus Drive , had been Illinois Central rai... |
The square is a tree @-@ lined section of Millennium Park with a large lawn . The area broadcasts free wifi wireless technology . The square has earned a reputation as an outdoor culture spot by hosting a wide range of cultural events such as local and international art and photography exhibitions , as well as occasio... |
In 2005 , Millennium Park was marked for updates and improvements . Benches were to be added to the 56 original benches . Landscape architect Kathryn Gustafson designed 14 new 320 @-@ pound ( 145 @.@ 1 kg ) , aluminum β Maggie benches β benches in Millennium Park , mostly in Wrigley square , in honor of Mayor Daley β ... |
The square was intended to serve as an exhibit space for outdoor sculpture as well as small cultural performances , according to Christopher Perille , vice president of the Wrigley Square Foundation . The square 's peristyle monument is in remembrance of the corporation , foundations , and individuals who made Millenn... |
An architectural model of Wrigley Square and Millennium Monument , designed by O 'Donnell , Wicklund , Pigozzi and Peterson Architects , Inc . ( OWP & P ) in 2000 , is on display at the Harold Washington Library Center .
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= = = Original peristyle = = =
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In 1917 , the original peristyle was designed by renowned Chicago planner Edward H. Bennett , who was Daniel Burnham 's partner in the Plan of Chicago and who was known for designing the nearby Buckingham Fountain . It was located in Grant Park in the same location as the current Wrigley Square . The original peristyl... |
= = = Millennium Monument = = =
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A gift from the William Wrigley , Jr . Company , the limestone replica peristyle rises to a height of nearly 40 feet ( 12 @.@ 2 m ) ( one source says the columns were planned to rise to 36 feet ( 11 @.@ 0 m ) ) , restoring a classical elegance to Grant Park . The William Wrigley , Jr . Foundation contributed $ 5 milli... |
The David Dillon and Michael Patrick Sullivan ( of OWP & P ) design is based on original drawings by Bennett found in the Chicago Park District 's archive .
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The naming rights of the space belong to Wm . Wrigley Jr , the foundation that created the world β s famous chewing gum . Wrigley Company officials , including William Wrigley , Jr . II , wanted to contribute to Millennium Park , and the historic aspect of the peristyle was attractive to them partly because the origin... |
The 24 paired , fluted columns are the same height as the original peristyle . However , the structure was scaled down to an 80 @-@ foot ( 24 @.@ 4 m ) diameter in order to accommodate the accessible ramp that runs behind the monument . Each of the limestone columns is cut from an Indiana quarry and made of five 2 @,@... |
The front of the monument has a dedication plaque ( pictured left ) . In addition , on the reverse side in approximately the same location , the monument has a special plaque commemorating John H. Bryan 's contribution as the head of fundraising for the Park .
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The original model of the Millennium Monument was the starting point of the Peristyle appearance in Chicago . To this day , it is said to not compare to the once β commanding presence β that once stood in its place , before being demolished and replaced with an underground parking garage . The new monument was downsiz... |
= Homologous recombination =
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Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA . It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA , known as double @-@ strand breaks . Homologous recombinatio... |
Although homologous recombination varies widely among different organisms and cell types , most forms involve the same basic steps . After a double @-@ strand break occurs , sections of DNA around the 5 ' ends of the break are cut away in a process called resection . In the strand invasion step that follows , an overh... |
Homologous recombination is conserved across all three domains of life as well as viruses , suggesting that it is a nearly universal biological mechanism . The discovery of genes for homologous recombination in protists β a diverse group of eukaryotic microorganisms β has been interpreted as evidence that meiosis emer... |
= = History and discovery = =
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In the early 1900s , William Bateson and Reginald Punnett found an exception to one of the principles of inheritance originally described by Gregor Mendel in the 1860s . In contrast to Mendel 's notion that traits are independently assorted when passed from parent to child β for example that a cat 's hair color and it... |
In 1947 , the microbiologist Joshua Lederberg showed that bacteria β which had been assumed to reproduce only asexually through binary fission β are capable of genetic recombination , which is more similar to sexual reproduction . This work established E. coli as a model organism in genetics , and helped Lederberg win... |
= = In eukaryotes = =
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Homologous recombination ( HR ) is essential to cell division in eukaryotes like plants , animals , fungi and protists . In cells that divide through mitosis , homologous recombination repairs double @-@ strand breaks in DNA caused by ionizing radiation or DNA @-@ damaging chemicals . Left unrepaired , these double @-... |
In addition to repairing DNA , homologous recombination also helps produce genetic diversity when cells divide in meiosis to become specialized gamete cells β sperm or egg cells in animals , pollen or ovules in plants , and spores in fungi . It does so by facilitating chromosomal crossover , in which regions of simila... |
= = = Timing within the mitotic cell cycle = = =
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Double @-@ strand breaks can be repaired through homologous recombination or through non @-@ homologous end joining ( NHEJ ) . NHEJ is a DNA repair mechanism which , unlike homologous recombination , does not require a long homologous sequence to guide repair . Whether homologous recombination or NHEJ is used to repai... |
Cyclin @-@ dependent kinases ( CDKs ) , which modify the activity of other proteins by adding phosphate groups to ( that is , phosphorylating ) them , are important regulators of homologous recombination in eukaryotes . When DNA replication begins in budding yeast , the cyclin @-@ dependent kinase Cdc28 begins homolog... |
= = = Models = = =
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Two primary models for how homologous recombination repairs double @-@ strand breaks in DNA are the double @-@ strand break repair ( DSBR ) pathway ( sometimes called the double Holliday junction model ) and the synthesis @-@ dependent strand annealing ( SDSA ) pathway . The two pathways are similar in their first sev... |
The RPA protein , which has high affinity for single @-@ stranded DNA , then binds the 3 ' overhangs . With the help of several other proteins that mediate the process , the Rad51 protein ( and Dmc1 , in meiosis ) then forms a filament of nucleic acid and protein on the single strand of DNA coated with RPA . This nucl... |
= = = = DSBR pathway = = = =
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After the stages of resection , strand invasion and DNA synthesis , the DSBR and SDSA pathways become distinct . The DSBR pathway is unique in that the second 3 ' overhang ( which was not involved in strand invasion ) also forms a Holliday junction with the homologous chromosome . The double Holliday junctions are the... |
Whether recombination in the DSBR pathway results in chromosomal crossover is determined by how the double Holliday junction is cut , or " resolved " . Chromosomal crossover will occur if one Holliday junction is cut on the crossing strand and the other Holliday junction is cut on the non @-@ crossing strand ( in Figu... |
= = = = SDSA pathway = = = =
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Homologous recombination via the SDSA pathway occurs in cells that divide through mitosis and meiosis and results in non @-@ crossover products . In this model , the invading 3 ' strand is extended along the recipient DNA duplex by a DNA polymerase , and is released as the Holliday junction between the donor and recip... |
During mitosis , the major homologous recombination pathway for repairing DNA double @-@ strand breaks appears to be the SDSA pathway ( rather than the DSBR pathway ) . The SDSA pathway produces non @-@ crossover recombinants ( Figure 4 ) . During meiosis non @-@ crossover recombinants also occur frequently and these ... |
= = = = SSA pathway = = = =
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The single @-@ strand annealing ( SSA ) pathway of homologous recombination repairs double @-@ strand breaks between two repeat sequences . The SSA pathway is unique in that it does not require a separate similar or identical molecule of DNA , like the DSBR or SDSA pathways of homologous recombination . Instead , the ... |
As DNA around the double @-@ strand break is cut back , the single @-@ stranded 3 ' overhangs being produced are coated with the RPA protein , which prevents the 3 ' overhangs from sticking to themselves . A protein called Rad52 then binds each of the repeat sequences on either side of the break , and aligns them to e... |
= = = = BIR pathway = = = =
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During DNA replication , double @-@ strand breaks can sometimes be encountered at replication forks as DNA helicase unzips the template strand . These defects are repaired in the break @-@ induced replication ( BIR ) pathway of homologous recombination . The precise molecular mechanisms of the BIR pathway remain uncle... |
The BIR pathway can also help to maintain the length of telomeres ( regions of DNA at the end of eukaryotic chromosomes ) in the absence of ( or in cooperation with ) telomerase . Without working copies of the telomerase enzyme , telomeres typically shorten with each cycle of mitosis , which eventually blocks cell div... |
Maintaining telomere length is critical for cell immortalization , a key feature of cancer . Most cancers maintain telomeres by upregulating telomerase . However , in several types of human cancer , a BIR @-@ like pathway helps to sustain some tumors by acting as an alternative mechanism of telomere maintenance . This... |
= = In bacteria = =
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Homologous recombination is a major DNA repair process in bacteria . It is also important for producing genetic diversity in bacterial populations , although the process differs substantially from meiotic recombination , which repairs DNA damages and brings about diversity in eukaryotic genomes . Homologous recombinat... |
= = = RecBCD pathway = = =
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The RecBCD pathway is the main recombination pathway used in many bacteria to repair double @-@ strand breaks in DNA , and the proteins are found in a broad array of bacteria . These double @-@ strand breaks can be caused by UV light and other radiation , as well as chemical mutagens . Double @-@ strand breaks may als... |
In this pathway , a three @-@ subunit enzyme complex called RecBCD initiates recombination by binding to a blunt or nearly blunt end of a break in double @-@ strand DNA . After RecBCD binds the DNA end , the RecB and RecD subunits begin unzipping the DNA duplex through helicase activity . The RecB subunit also has a n... |
Upon encountering a Chi site , the activity of the RecBCD enzyme changes drastically . DNA unwinding pauses for a few seconds and then resumes at roughly half the initial speed . This is likely because the slower RecB helicase unwinds the DNA after Chi , rather than the faster RecD helicase , which unwinds the DNA bef... |
= = = RecF pathway = = =
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Bacteria appear to use the RecF pathway of homologous recombination to repair single @-@ strand gaps in DNA . When the RecBCD pathway is inactivated by mutations and additional mutations inactivate the SbcCD and ExoI nucleases , the RecF pathway can also repair DNA double @-@ strand breaks . In the RecF pathway the Re... |
Although the proteins and specific mechanisms involved in their initial phases differ , the two pathways are similar in that they both require single @-@ stranded DNA with a 3 β end and the RecA protein for strand invasion . The pathways are also similar in their phases of branch migration , in which the Holliday junc... |
= = = Branch migration = = =
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Immediately after strand invasion , the Holliday junction moves along the linked DNA during the branch migration process . It is in this movement of the Holliday junction that base pairs between the two homologous DNA duplexes are exchanged . To catalyze branch migration , the RuvA protein first recognizes and binds t... |
= = = Resolution = = =
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