Polytenechromosomes（多线染色体）inDrosophilasalivaryglands canbeusedtomapdeletionsfemalemaleASALIVARYGANGLIONGONADGLAND(BRAIN)embryopupaSCALE1mm1stinstarlarvaBprepupaGANGLION2ndinstarlarvaSALIVARYTRACHEAFAT BODYOVARYGLANDSTOMACHINTESTINE3rd instar larvaFig. 2. Diagrams of third-instar larvae of Drosophila melanogaster. A:Lateral viewshowing approximate locations of salivary glands,ganglion,and gonads. The gonad ortestis of the male, here represented, is larger than the gonad or ovary of the female, shownin B.(After unpublished drawing by C.B.Bridges.) B:Dorsal viewof female larvawith additional detail,(Adapted from E.Strasburger.)
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 14-11 Polytene Polytene chromosomes ( chromosomes (多线染色体) in Drosophila Drosophila salivary salivary glands can be used to map deletions glands can be used to map deletions
Interphase chromosomesreplicate 10 times.RightarmofXchromosomechromosome3Each chromosome consistsof210(1024)doublehelices.Reproducible bandsMitoticprovidedetailed physicalchromosomesguide to gene mapping.ChromocenterTotalofabout5000bands(heterochromatin)rangingfrom3kb to150kb.Chromosome4b)Alignrtenechromosomes00Rightarmofchromosome2Leftarmofchromosome2-Interband20umLeftarmofchromosome3Bano14-12
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 14-12 Interphase Interphase chromosomes chromosomes replicate 10 times. replicate 10 times. Each chromosome consists Each chromosome consists of 210 (1024) double helices. (1024) double helices. Reproducible bands Reproducible bands provide detailed physical provide detailed physical guide to gene mapping. guide to gene mapping. Total of about 5000 bands Total of about 5000 bands ranging from 3 kb to 150 kb. ranging from 3 kb to 150 kb
Drosophila deletion heterozygotes form visible deletion loops inthepairedpolytenechromosomes14-13
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 14-13 Drosophila Drosophila deletion deletion heterozygotes heterozygotes form visible deletion loops in form visible deletion loops in the paired the paired polytene polytene chromosomes chromosomes
Deletions can be used to locate genes3C3BRegionsDeletionsto assignBandnumbersl123456/1234567891011genes to bands onDrosophilaSmall segmentpolyteneofbandedchromosomes.polytenechromosomeComplementationPhenotypeoftests crossingSpecificmutation/Deldeletion mutantsdeletionsheterozygotewith mutantgenesDf258-45w-rst+fatofinterests.Df67c23w-rst+fatDf N8Deletionw-rst-faDf264-32wrst-faheterozygoteDf264-33w+rst+farevealsrstfaWchromosomalRegionsofgeneslocation ofmutantDrosophila white (w+),roughest (rst+),and facetgene.(fa+)genesontheXchromosome14-14
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 14-14 Deletions can be used to locate genes Deletions can be used to locate genes Deletions to assign Deletions to assign genes to bands on genes to bands on Drosophila Drosophila polytene polytene chromosomes. chromosomes. Complementation Complementation tests crossing tests crossing deletion mutants deletion mutants with mutant genes with mutant genes of interests. of interests. Deletion Deletion heterozygote heterozygote reveals reveals chromosomal chromosomal location of mutant location of mutant gene. Drosophila white (w+), roughest (rst+), and facet (fa+) genes on the X chromosome
2. Duplications chromosomes have extra copies of some genes(a)TypesofduplicationsDuplications addTandemduplicationsmaterial to theNormalchromosomeABCDEFGgenome.ABCBCDGSameorderReverseorderBANontandem(dispersed)duplicationsABCDBGSameorderReverseorderABCDBG(b)ChromosomebreakagecanproduceduplicationsXraysbreakonechromosomeintwoplacesNontandemduplicationFig.12.8Xraysbreakhomologous15chromosomeinoneplace
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 14-15 2. Duplications chromosomes ha 2. Duplications chromosomes have extra copies of some genes ve extra copies of some genes Fig. 12.8 Duplications add material to the genome