Autosomal genes can also exhibit linkagePObct/bc+×btc/b+cb ct/b+ cF, (all identical)Test crossbc+/b+c × bc/bcTest2934bct/bc-Parental2934 + 2768 ×100 =77%crossclasses2768 b+ c/b c7419progeny871bc/b cRecombinant871+846X100=23%classes846 bt ct/b c7419Total 7419Fig. 5.45-6
5-6 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Autosomal genes can also exhibit linkage Fig. 5.4
Summaryof linkageIn dihybrid crosses, departures from a 1:l:l:1 ratio ofF gametes indicate that the two genes are linked on thesamechromosome.Testcrosses with one parenthomozygous for recessivealleles of bothgenes canhelp determineif linkedParental class outnumbers recombinant classdemonstrateslinkage.Anon-2:0:0:2 segregation pattern ofF2 progeniesindicatesgeneticrecombination5-7
5-7 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display In dihybrid dihybrid crosses, departures from a 1:1:1:1 ratio of crosses, departures from a 1:1:1:1 ratio of F1 gametes indicate that the two genes are linked on the gametes indicate that the two genes are linked on the same chromosome. same chromosome. Testcrosses with one parent homozygous for recessive Testcrosses with one parent homozygous for recessive alleles of both genes can help determine if linked. alleles of both genes can help determine if linked. Parental class outnumbers recombinant class Parental class outnumbers recombinant class demonstrates linkage. demonstrates linkage. A non -2:0:0:2 segregation pattern of 2:0:0:2 segregation pattern of F2 progenies progenies indicates genetic recombination. indicates genetic recombination. Summary of linkage Summary of linkage
TABLE5.2PropertiesofLinkedVersusUnlinkedGenesLinked GenesParentals>recombinants(RF<5o%)Linkedgenesmustbe syntenicand sufficientlyclosetogetheronthe same chromosome so that they do not assortindependently.UnlinkedGenesParentals=recombinants(RF=50%)Occurseitherwhen genesareon differentchromosomesorwhenthey are sufficientlyfar apartonthe samechromosome.5-8
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T. H. Morgan's experimentPQwwytytxowty/Yow+wyty x owyt/yF, males4484W yt /Ywt:brick-red eyesParentaltypes=4413wt y/Y4484+4413w: white eyes× 100=99%9026yt: brown body76wt y+ / Yy: yellow bodyRecombinanttypes:53Y:Y chromosomewy/Y76+53× 100= 1%Total 90269026Fig.5.25-9
5-9 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Fig. 5.2 w +: brick-red eyes w: white eyes y +: brown body y: yellow body Y: Y chromosome T. H. Morgan’s experiment
PWX?aAF1AQWVF2malesWWVAParentalParentalRecombinantRecombinant~99%~1%Fig.5.35-10
5-10 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Fig. 5.3