3Figure 15.2 The chromosomal basis of Mendel’s laws. P GenerationYellow-round seeds (YYRR)Green-wrinkled seeds (yyrr)YryYRRryMeiosisFertilizationRYyrGametesAll F1 plants produce yellow-round seeds (YyRr).F1 GenerationRRyyrrYYMeiosisLAW OF SEGREGATION The two alleles for each gene separate during gamete formation.LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation.RrrRMetaphase IYyYy11RrrRAnaphase IYyYyRrrRFigure 15.2 The chromosomal basis of Mendel’s laws.22YyMetaphase IIYyyYYyYYyyGametesRRrrrrRR1/4YR1/4yr1/4Yr1/4yRF2 GenerationAn F1 F1 cross-fertilization3Fertilization recombines the R and r alleles at random.3Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation.9: 3: 3: 1
8All offspring had red eyes. Figure 15.4EXPERIMENTP GenerationF1 GenerationAll offspring had red eyes.RESULTSF2 GenerationCONCLUSIONP GenerationwwXXXYwwSpermEggsF1 GenerationwwwwFigure 15.4 Inquiry: In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?wSpermEggswwF2 Generationwwwwww
12(d) The haplo-diploid system Figure 15.644 XYParents44 XX22 Xor22 Y22 XSpermEgg44 XXor44 XYZygotes (offspring)(a) The X-Y system22 XX22 X(b) The X-0 system76 ZW76 ZZFigure 15.6 Some chromosomal systems of sex determination.(c) The Z-W system32 (Diploid)16 (Haploid)(d) The haplo-diploid system
19Cell division and X chromosome inactivation Figure 15.8X chromosomesAllele for orange furEarly embryo:Allele for black furCell division and X chromosome inactivationTwo cell populations in adult cat:Active XInactive XActive XBlack furOrange furFigure 15.8 X inactivation and the tortoiseshell cat.
22Wild type (gray-normal) FigureEXPERIMENTP Generation (homozygous)Double mutant (black body, vestigial wings)Wild type (gray body, normal wings)b b vg vgb b vg vgF1 dihybrid (wild type)Double mutantTESTCROSSb b vg vgb b vg vgTestcross offspringEggsb vgb vgb vgb vgWild type (gray-normal)Black- vestigialGray- vestigialBlack- normalb vgSpermFigure 15.9 Inquiry: How does linkage between two genes affect inheritance of characters?b b vg vgb b vg vgb b vg vgb b vg vgPREDICTED RATIOSIf genes are located on different chromosomes:1:1:1:1If genes are located on the same chromosome and parental alleles are always inherited together:1:1::RESULTS965:944:206:185
24F1 dihybrid female and homozygous recessive male in testcross Figure 15.UN01b+ vg+b vgF1 dihybrid female and homozygous recessive male in testcrossb vgb vgb+ vg+b vgMost offspringFigure 15.UN01 In-text figure, p. 294orb vgb vg
43A deletion removes a chromosomal segment. Figure 15.14(a) DeletionABCDEFGHA deletion removes a chromosomal segment.ABCEFGH(b) DuplicationABCDEFGHA duplication repeats a segment.ABCDEFGH(c) InversionABCDEFGHAn inversion reverses a segment within a chromosome.ADCBEFGHFigure Alterations of chromosome structure.(d) TranslocationABCDEFGHMNOPQRA translocation moves a segment from one chromosome to a nonhomologous chromosome.MNOCHFEDGABPQR
51Normal Igf2 allele is expressed. Figure 15.17Normal Igf2 allele is expressed.Paternal chromosomeMaternal chromosomeNormal-sized mouse (wild type)Normal Igf2 allele is not expressed.(a) HomozygoteMutant Igf2 allele inherited from motherMutant Igf2 allele inherited from fatherNormal-sized mouse (wild type)Dwarf mouse (mutant)Figure Genomic imprinting of the mouse Igf2 gene.Normal Igf2 allele is expressed.Mutant Igf2 allele is expressed.Mutant Igf2 allele is not expressed.Normal Igf2 allele is not expressed.(b) Heterozygotes