Molecular Basis of Genetic Traits St

8/18/2019 Molecular Basis of Genetic Traits St

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Molecular Basis Of Genetic

Traits


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Wrinkled Peas

• SS – starch grains are large and simple;contain larger amounts of starch; lowerle els of sucrose; higher water content;larger si!e seeds

• Seed"shape gene encodes starch"#ranching en!$me SB%&

• 'ifference #etween S and s allele – not asingle #ase pair change #ut a ())"#pinsertion *transposon+ in S gene


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'warfism in Peas

• One of the , pairs of traits that Mendel studied inpeas as he worked out the #asic rules ofinheritance was dwarf"tall-

• The recessi e gene " toda$ called le " turns outto encode an en!$me that is defecti e inena#ling the plant to s$nthesi!e G. *gi##erelin+-

•The dominant gene/

Le/ encodes a functioningen!$me permitting normal G. *gi##erelin+

s$nthesis and making the 0tall0 phenot$pe


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'warfism in Peas

• 'uring the 123)s 4apanese scientists isolated agrowth"promoting su#stance from cultures of afungus that parasiti!es rice plants- The$ called it

gibberellin -• .fter the dela$ caused #$ World War &&/ plantph$siologists in other countries succeeded inisolating more than 3) closel$"related

compounds-• One of the most acti e of these 5 and one foundas a natural hormone in the plants themsel es 5is gibberellic acid *GA +-


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'warfism in Peas

• G. has a num#er of effects on plant growth/ #utthe most dramatic is its effect on stem growth -

• When applied in low concentrations to a #ush or0dwarf0 #ean/ the stem #egins to grow rapidl$-The length of the internodes #ecomes so greatthat the plant #ecomes indistinguisha#le fromclim#ing or 0pole0 #eans-

• G. seems to o ercome the genetic limitations inman$ dwarf arieties-


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Effects of gibberellins on geneexpression

• Gi##erellins e6ert their effects #$ alteringgene transcription


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Effects of gibberellins on geneexpression

• The steps7 – Gi##erellin enters the cell and – #inds to a solu#le receptor protein called GID1 *0gi##erellin"

insensiti e dwarf mutant 10+ which now can #ind to a – comple6 of proteins * SCF + responsi#le for attaching u#i8uitin to

one or another of se eral DELLA proteins - – This triggers the destruction of the '%99. proteins #$

proteasomes- – '%99. proteins normall$ #ind a gi##erellin"dependent

transcription factor/ called GA- !"# / pre$enting it from #indingto the

– ':. of control se8uences of genes that are turned on #$gi##erellin-

– 'estruction of the '%99. proteins relie$es this inhi#ition and – gene transcription #egins-


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Plant 'warfs

• The dwarf arieties of rice and wheat that ha epla$ed such an important part in the %greenre$ol&tion% carr$ mutant genes that

– interfere with the s$nthesis of their gi##erellins *in thecase of rice+ or – for wheat/ reduce their a#ilit$ to respond to their own

gi##erellins *#ecause of mutant genes for a '%99.protein+

– 'warf arieties of sorghum and 5 more recentl$ 5mai!e *corn+ also e6ist/ #ut in these cases/ themutation interferes with a&xin transport/ notgi##erellin acti it$--


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':. Pol$merases and uman'iseases


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uman ':. Pol$merases


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• ':. pol$merases are re8uired for all ':.s$nthetic processes-

• Thus/ mutations in ':. pol$merases orchanges in their e6pression could #emanifested #$ alterations in ':.replication/ in cell c$cle progression and/most prominentl$/ in mutagenesis-


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•


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• %pigenetic silencing of gene e6pression iscommon in man$ human tumours and mightaffect ':. pol$merases-

• . sur e$ of ':. pol$merase genes on the


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Prader"Willi and snoC:.s

• snoC:.s – small nucleolar C:.s/ non"coding

• . paternall$ deri ed deletion of the B&&"(D cluster of snoC:.s is responsi#le forke$ aspects of the Prader"Willi phenot$pe

• The first disorder found to #e associatedwith loss of e6pression of noncodingsnoC:.s


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The Genetics of Tomato Shape


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• Eor tomato *Solanum l$copersicum+/ culti atedt$pes #ear fruit of ar$ing si!es with man$di erse shapes-

• The locus sun comprises a maFor 8uantitati etrait locus e6plaining D( of the phenot$pic

ariation in a cross that was deri ed from the S-l$copersicum ariet$ HSun1IJK/L which haselongated shaped fruit/ and its wild relati e S-pimpinellifolium/ which has round fruit


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• Eine mapping indicates that sun resides ina region of the tomato genome on theshort arm of chromosome , that carriessmall"scale insertions/ deletions/ andtandem duplications-

• One insertion/ estimated to #e 3) k#/ ispresent in Sun1IJK *#ut not in 9.1D(2+and is linked to fruit shape


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• omparati e se8uence anal$sis of thelocus showed that the si!e difference wasdue to the insertion of a KJ-,"k# segmentpresent in Sun1IJK #ut a#sent from9.1D(2

• This insertion completel$ co"assorted with

the phenot$pe/ impl$ing that it underliesthe molecular #asis of elongated fruitshape-


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• . Southern #lot showed that 9.1D(2contained onl$ one cop$ of this se8uence/whereas Sun1IJK contained two copies-

• Both accessions shared a cop$ of thislocus on chromosome 1)/ suggesting thatthe inserted segment on chromosome , inSun1IJK originated from chromosome1)


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• . much higher transcript le el of & '1K waso#ser ed in the :&9 carr$ing the Sun1IJK allelein comparison with the :&9 carr$ing the 9.1D(2allele-

• The highest transcript le els of & '1K werefound in $oung de eloping fruit D da$s afteranthesis-

• Transcript le els of the disrupted gene '%E91showed an in erse e6pression pattern relati e to& '1K7 When & '1K was e6pressed/ '%E91was not *and ice ersa+


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• Eruit"shape phenot$pe was h$pothesi!ed to #e dosage"dependent/ #ecause hetero!$gous sun :&9 plants e6hi#itan intermediate fruit shape relati e to that of the parentsin #oth the 9.1D(2 and Sun1IJK #ackgrounds-

• :orthern #lots demonstrated that & '1K was e6presseda#out twofold higher in indi iduals homo!$gous for thetransposed fragment than in hetero!$gous plants-

• Similarl$/ '%E91 was e6pressed a#out twofold higher inhomo!$gous indi iduals lacking the transposed fragmentthan in hetero!$gotes

Molecular Basis of Genetic Traits St

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