Forgenes wandy:Recombinantfrequency(RF)=Recombinant classes/Total classes5-11
5-11 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display For genes w and y : Recombinant frequency (RF) = Recombinant classes/Total classes
CrossSeriesACrossSeriesBPPwWO8w+WF1F1w+OSF2malesF2maleswWwWWAParentalRecombinantParentalParentalRecombinantParentalRecombinantRecombinant~1%~99%~1%~99%Parental and recombinant classes are opposite of one another inthesetwo crosses.Similar percentages of recombinant and parental types showthat thefrequency of recombination isindependent of thearrangement ofalleles.5-12Fig.5.3
5-12 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Parental and recombinant classes are opposite of one another in Parental and recombinant classes are opposite of one another in these two crosses. these two crosses. Similar percentages of recombinant and parental types show Similar percentages of recombinant and parental types show that the frequency of recombination is independent of the that the frequency of recombination is independent of the arrangement of alleles. arrangement of alleles. Fig. 5.3
E,females4genotypes(gametes)Two questions Morgan faced:1. What was the source of gene separation?2. Why did the recombinant frequency vary?1.3%37.2%versusW-mWL5-13
5-13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Two questions Morgan faced: Two questions Morgan faced: 1. What was the source of gene separation? 2. Why did the recombinant frequency vary? 1.3% versus 37.2% w——y w——m w y + F1 females w + y 4 genotypes (gametes)
5.3 Recombination:A result of crossing-overduringmeiosis1909-Frans A.Janssens reported chiasmata, regions inwhich nonsister chromatids of homologouschromosomes cross over each other during prophase ofthe first meiotic divisionFransA.Janssens(1865-1924)5-14
5-14 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1909 – Frans A. Janssens Janssens reported reported chiasmata chiasmata, regions in , regions in which nonsister nonsister chromatids chromatids of homologous of homologous chromosomes cross over each other during prophase of chromosomes cross over each other during prophase of the first meiotic division. the first meiotic division. Frans A. Janssens (1865-1924) 5.3 Recombination: A result of crossing-over during meiosis
Morgan'sexplanation:Morgan suggested chiasmata were the sites ofchromosome breakage and exchange resulting ingeneticrecombinationcentromerechromatidchiasmachiasmacentromere5-15
5-15 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Morgan ’s explanation: s explanation: centromere centromere chromatid chiasma chiasma Morgan suggested Morgan suggested chiasmata chiasmata were the sites of were the sites of chromosome breakage and exchange resulting in chromosome breakage and exchange resulting in genetic recombination. genetic recombination