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Art and Photos in PowerPoint Concepts of Genetics Ninth Edition Klug Cummings Spencer Palladino Chapter 4 Extensions of Mendelian Genetics 41 Alleles Alter Phenotypes in Different Ways We ve focused on complete dominance but there are many ways that genotype and phenotype can be related 42 Geneticists Use a Variety of Symbols for Alleles The simplest is capital letters for the completely dominant allele and lower case for the recessive allele If you are confused by nomenclature suggest you rewrite things to make them simpler 43 Neither Allele ls Dominant In Incomplete or Partial Dominance In incomplete dominance the heterozygote has a phenotype intermediate between the two possible homozygotes W mm minim m Figure41 43 Neither Allele ls Dominant In Incomplete or Partial Dominance Whether an allele is completely dominant or incompletely dominant can depend upon the phenotype eg TaySachs disease 43 NeitherAIIeIe Is Dominant In Incomplete or Partial Dominance eg TaySachs disease m y 39 39 39 individuals and only those individuals die very early in the rst few years of life lncompletely dominant phenotype heterozygotes have al as much hexosaminidase A enzyme activity as dominant homozygotes 44 In Codominance the Influence of Both Alleles in a Heterozygote Is Clearly Evident 441 The MN Blood Group Individuals can express the M glycoprotein the N glycoprotein or both glycoproteins 45 Multiple Alleles ofa Gene May Exist in a Population 451 The ABC Blood Groups 452 The A and B Antigens Individuals can express the A antigen the B antigen both antigens or neither antigen TABLE 1 P 2 is Phenotypes in the Offspring of Parents with All Possible ABO Blood Group Combinations Assuming Heterozygosity Whenever Possible Parents Potential OFFSPring Phenotypes Genotypes A B AB 0 A x A Iquot i0 X i 0 34 7 7 14 5 gtlt B I I0 X IB 0 34 14 Oxo IOIOXIOID 7 7 7 all AXB I IOXIBO 14 14 14 14 AXAE WaxAI 12 14 14 7 AgtltO MaxOI 12 7 7 12 BgtltAB IBIOXIAIE 14 12 14 Bgtlto FlaxOla 7 12 7 12 AB x 0 IA l3 x I O 12 12 7 AB gtlt AB IA I X IA quot 14 14 12 new ememm ea San Educ ian lnc Tabe41 m4 0 0N e 39 a l mm l fan AFN knlvw Vi Wl Lexi y Dquot an 7 0 cm 139 nus l ow s Huii sinn Mi EFL391quot PM 7 J M JN 33mquot in mm 1mm 1 77 W E r i 5 l n mum en w neie I 11 If M 33mm I quot an nine g emu1 saw vMemm assmm in Figure42 45 Multiple Alleles of a Gene May Exist in a Population 453 The Bombay Phenotype In rare cases an AB parent or even two AB parents can have a type 0 child This is called the Bombay phenotype Envy vMemm shaman lnc Figure 43 45 Multiple Alleles of a Gene May Exist in a Population 454 The white Locus in Drosophila Envy vMemm e m mum in TABLE 42 Some of the Alleles Present at the White Locus of Drasophila Allele Name w W its w Whiteapricut wbF whiterbuff wbl whiteblood wL whiterco ree W 9 Wk iteeusm Wm white mottled orange Wm Whi tesatsuma w F wh iterspotted wt whitetinged Envy vMemm easanEducmmn m Eye Color pure white yellowish orange light buff yellowish ruby deep ruby yellowish pink light mottled orange deep ruby ne grain yellow mottling light pink Tnbe42 46 Lethal Alleles often Represent Essential Genes Essential is defined as necessary for viability 461 Recessive Lethal Mutations Dominant alleles can sometimes also have recessive lethal phenotypes Envy mama ea m mmquot inc cross A cross a Cross c p k x Emi 12 gtlt m agouti agouti yellow yellnw agouti yellow agou l l l agouli yellow l v I H agouti yellow yellow lemal l l 2 3 Yellow 12 agouti lill39SEZ l39lL 3 59W 12 yellow SUMWVS All survive agnuti mouse vallow mouse Envy mama ea m mmquot inc Figure 44 46 Lethal Alleles Represent Essential Genes 462 Dominant Lethal Mutations The yellow allele of agouti AV is dominant for coat color but it is also recessive lethal So we never see AYAY homozygotes and we see a 21 ratio of yellow to agouti in when AAY heterozygotes are crossed Envy mama ea m mmquot inc 47 Combinations of Two Gene Pairs With Two Modes of Inheritance Modify the 9331 Ratio Envy vMemm e m Emmi inc 48 Phenotypes Are Often Affected by More Than One Gene 481 Epistasis Envy vMemm e m mum inc commquot mun im swim in mm mm aim i X Fig i i m a mm m Q i at m 5 7 mm mm may may may 24 um AB magma M Q 3 d boll Mnm nlul in oi ili amazing 01 ail offspring Fmai probabilities i i m A 315 pigmnmnd me A m pigmented T m as 4 ms nigmmea type AB m a 7 ans pigmenxeu lype a van 7 Insalb in IypuA Vd aihinn 24 AB 2115 album WP AB 4 w a 7 ms albino vav a Final phanmypic min m sns ans me me ms W mm maing inc Figured m mm39 M mama mm 1 uni 11 a 1 mum MW 1 6 In 4quot mw Aa quot39 quot3quot 7 Inf awrva In 23333 mm 611mm mm mmmm mugW alumni1 l w glamm mm W 7 6 mm A quotWm M 115mm 7 smaYyneAa mus 315ml a mer w 31111 was new Mimim a mum sawmm ms mm Figure16 Epistasis in Mouse Coat Color Blocked in c mutants Phenylalanine Tyrosine DO PA 3 ydroxyphenylala ne I Melanins Eumelanin Blocked in albino mutants cc homozygotes Phaeomelanin Switched by the product of agouti gene the A allele Envy menu 6 m mum in Many ratios can exist Dillybrid ralio Mndi ed ratios 116 216 216 416 916A B 916 916 915 a 1 416 m 1215 quot15 m quot 52 15 emu rm 316 116 E 11621s 31SEEB 316 716 116 416 7 116 E mess76 116 116 116 W mm mmmquot m Figure17 48 Phenotypes Are Often Affected by More Than One Gene 482 Novel Phenotypes 49 Complementation Envy maxim e m mmquot m albino black albino yellow green Pea whlte Squash sphere Chicken while colored Mouse whilespn ed white colored krlangular ans somy and ails red black W mm mama m Figured Sphere my mm ummmn m FigureAS Figure 410 49 Complementation Analysis Can Determine if Two Mutations Causing a Similar Phenotype are Alleles Envy vMemm e m mmquot lnc Case 2 Mulaiiuns are in dillerenl lualicns within lhe same gene case 1 Mulalions are in separaxe genes Gene 1 Gene Gene 1 Gene 2 WP i Homologs Homnlugs One normal copy at each gene is presem Genei is muia C Nu m in all cases while Gene 2 is normal ompiemenmiun occurs 5 complemenlalinn occur AND DO No1 DEVELOP WINGS 15 Envy vMemm easanEducmlan lnc Figure 411 10 albino albino green Pea Squash Chicken while colored Mouse white colored whilespotted triangular 616 scaly and 315 red black W mm mamch inc Figured 410 Expression of a Single Gene May Have Multiple Effects This phenomenon is called pleiotropy Many genes are pleiotropic let s discuss PKU as an example using OMIM at httpwwwncbinmnihgov Envy vMemm e m mum inc 11