Chapter 5 Linkage, Recombination, and the Mapping of Genes on Chromosomes 5-1
5-1 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Linkage, Recombination, and the Linkage, Recombination, and the Mapping of Genes on Chromosomes Mapping of Genes on Chromosomes Chapter 5
Sections to study5.1 Gene linkage and recombination5.2 The Chi-square test and linkage analysis5.3 Recombination: A result of crossing-over duringmeiosis5.4Mapping:Locatinggenes along a chromosome5.5 Tetrad analysis in fungi5.6Mitotic recombination and genetic mosaics5-2
5-2 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 5.1 Gene linkage and recombination 5.1 Gene linkage and recombination 5.2 The Chi 5.2 The Chi-square test and linkage analysis square test and linkage analysis 5.3 Recombination: A result of crossing 5.3 Recombination: A result of crossing -over during over during meiosis meiosis 5.4 Mapping: Locating genes along a chromosome 5.4 Mapping: Locating genes along a chromosome 5.5 Tetrad analysis in fungi 5.5 Tetrad analysis in fungi 5.6 Mitotic recombination and genetic mosaics 5.6 Mitotic recombination and genetic mosaics Sections to study Sections to study
5.1Gene linkage and recombinationHIndependentassortmentGenes on differentchromosomesGametes福B3AB: Ab: aB: ab=l: 1: 1: 15-3
5-3 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 5.1 Gene linkage and recombination 5.1 Gene linkage and recombination A a B b a B A B a b A b Gametes AB: Ab: aB: ab=1: 1: 1: 1 Independent assortment Independent assortment Genes on different Genes on different chromosomes chromosomes
Genetic linkageTwo genes on the same chromosome segregate together.mm9GametesAB: Ab:aB: ab=2:0:0:25-4
5-4 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Genetic linkage Genetic linkage Two genes on the same chromosome segregate together. Two genes on the same chromosome segregate together. A a B b Gametes a b A B A B a b AB: Ab: aB: ab=2: 0: 0: 2
w and y genes are X-linked in DrosophilaPQwwyyt xowty/y+w+wyty × owy+/ymales-4484W yt /YThomas H.MorganParentaltypes:4413wt y/Y4484+4413× 100=99%wt: brick-red eyes9026w: white eyes76wt y+ /Yy+: brown bodyRecombinanttypes:53wy/yy: yellow body76+53×100=1%Total 90269026Y:Y chromosomeFig.5.25-5
5-5 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 w and y genes are X-linked in Drosophila Thomas H. Morgan
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
5-8 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display
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