GENETIC LINKAGEProblems to tryIndependent AssortmentLINKAGELINKAGE & parental typesMeiosis with no crossoverRecombination fraction, r, is a variable with a different value for each pair of loci.Estimating r & map distancer = (86+44)/(86+44+4292+4605)= 0.014, so 1.4 map unitsSlide Number 10An Example of LinkageLinkage of height and hairinessEVALUATING GAMETIC PROPORTIONS with test crossObserved proportions are not compatible with equal amounts of each gametic genotype.Expected equalitiesGetting a Value for rIf the F1 had Sg/sG genotype then the following is a typical result.Slide Number 18Crossing over in 3 linked loci3 linked loci (ordered HQR)Ordering loci on a chromosomeCONSTRUCTING THE MAPBacterial GENESBacterial SEXLINKAGE RECAPITULATIONVocabularyExam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg11GENETIC LINKAGEGENETIC LINKAGEGenes are connected together in a linear Genes are connected together in a linear order on chromosomes.order on chromosomes.The connectedness means all possible The connectedness means all possible gameticgametic genotypes are genotypes are NOTNOT produced produced EQUALLY frequently.EQUALLY frequently.Problems to try¾ P255 #2¾ P256 #6¾ There is no problem in Freeman in which you use data to estimated r, the recombination fraction.Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg33Independent AssortmentIndependent Assortment¾¾In a double heterozygote, In a double heterozygote, AaBbAaBb,,which which includes both includes both Ab/aBAb/aBandandAB/AB/abab, independent , independent assortment means that the segregation assortment means that the segregation of of AAand and aais independent of the is independent of the segregation of B and b, i.e., the segregation of B and b, i.e., the ABAB, , AbAb, , aBaB& & ababarrangements in the gametes arrangements in the gametes are expected to be equally frequent.are expected to be equally frequent.Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg44LINKAGELINKAGE¾¾Two (or more) loci have to be heterozygous to Two (or more) loci have to be heterozygous to ‘‘seesee’’linkage linkage (in transmission genetics).(in transmission genetics).¾¾Linkage is nonLinkage is non--independent assortment of independent assortment of alleles at separate loci during meiosis.alleles at separate loci during meiosis.¾¾Linkage is a reflection of the fact that loci Linkage is a reflection of the fact that loci occupy specific places on the DNA of occupy specific places on the DNA of chromosomes.chromosomes.Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg55LINKAGE & parental typesLINKAGE & parental types¾¾An individual produces more gametes that have its An individual produces more gametes that have its parental configuration than it produces gametes with parental configuration than it produces gametes with one allele from the father and one from the mother.one allele from the father and one from the mother.¾¾An An Ab/aBAb/aBindividual will produce more individual will produce more AbAband and aBaBgametes (the arrangement in the gametes that united gametes (the arrangement in the gametes that united to form it, and therefore called parental) than to form it, and therefore called parental) than ABABand and ababgametes (which are called recombinants).gametes (which are called recombinants).Meiosis with no crossoverMeiosis with no crossoverExam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg66Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg77Recombination fraction, Recombination fraction, rr, is a , is a variablevariable with a different value for with a different value for each pair of locieach pair of loci..¾¾The closer together two loci are the less The closer together two loci are the less the proportion of recombinant types.the proportion of recombinant types.¾¾rrtakes values between 0 and takes values between 0 and ½½..Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg88Estimating r & map distanceEstimating r & map distance¾¾For a pair of loci, the expected For a pair of loci, the expected proportionproportionof the of the two parental types is two parental types is 1 1 ––rr, and the expected , and the expected proportion of two recombinant types will sum to proportion of two recombinant types will sum to rr..¾¾Each parental type is expected to be equally Each parental type is expected to be equally frequent, so each type =(1frequent, so each type =(1--r)/2.r)/2.¾¾Each recombinant type has the expected Each recombinant type has the expected frequency of r/2.frequency of r/2.r = (86+44)/(86+44+4292+4605)= 0.014, so 1.4 map unitsr = (86+44)/(86+44+4292+4605)= 0.014, so 1.4 map unitsExam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg99Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg1010Gamete production in a double heterozygote.We will use H and Q as symbols for the loci.Hq/hQ is diploid genotypePossible gametes Hq HQ hq hQParental YESNONOYESRecombinant YES YESExpected proportions (1-r)/2 r/2 r/2 (1-r)/2Complete Linkage ½ 0 0 ½(r = 0.000…)Independent (r = ½)¼¼¼¼AssortmentExam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg1111An Example of LinkageAn Example of Linkage¾¾We will look at an example from the pea.We will look at an example from the pea.¾¾To look at linkage we have to have two To look at linkage we have to have two loci, so normally we have variation in two loci, so normally we have variation in two different characters.different characters.¾¾Variety Variety KKTALL PUBESCENT leavesTALL PUBESCENT leaves¾¾Variety Variety LLSHORT GLABROUS leavesSHORT GLABROUS leaves¾¾F1 is TALL PUBESCENT F1 is TALL PUBESCENTExam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg1212Linkage of height and hairinessLinkage of height and hairiness¾¾Variety K TALL PUBESCENTVariety K TALL PUBESCENTzzSSGGSSGG¾¾Variety L SHORT GLABROUSVariety L SHORT GLABROUSzzssggssgg¾¾The F1 genotype SG/The F1 genotype SG/sgsgslash notationslash notation¾¾Possible Possible gameticgameticgenotypes of F1:genotypes of F1:zzSGSGSgSgsGsGsgsg¾¾Expected proportions:Expected proportions:zz¼¼¼¼¼¼¼¼Exam 2 Lecture 4Exam 2 Lecture 4UIC UIC BioSBioS 101 Nyberg101 Nyberg1313EVALUATING GAMETIC EVALUATING GAMETIC PROPORTIONS with test crossPROPORTIONS with test crossThe most efficient way to determine the