Portland State University PDXScholar Dissertations and Theses Dissertations and Theses 8-20-1973 A test of the simple recessive hypothesis for the inability to taste phenyl-thio-urea: a family study Susan I. Wolf Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Biological and Physical Anthropology Commons, and the Genetics Commons Let us know how access to this document benefits ou.y Recommended Citation Wolf, Susan I., "A test of the simple recessive hypothesis for the inability to taste phenyl-thio-urea: a family study" (1973). Dissertations and Theses. Paper 2145. https://doi.org/10.15760/etd.2143 This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. A TEST Oll THE S!¥iPLE RECESSrV}".! EYPCT::i:IESIS FOR TEE INABILITY TO TASTE PHENYL·-rr·HIO .. UREA~ j.FAHI~YSTUDY. - , by SUSAN. I. WOLF. A thesis submitted in partial fulf.illment of the requirements for the degree of ltJASTER OF ARTS in j,NT 1rtiO PO WG Y Portland State University 1973 ·:, AN ABSTRACT OF THE THESIS OF Susan I. Wolf for the Master of Arts in Anthropology presented Auguat20, 1973, . ~~ .. Title, A Test of the Simple Recessive Hypothesis for the Inability to Taste Phenyl-thio-ureal A Family Study. APPROVED BY MEMBERS OF TEE THES~ITTEEI V~rc R. Feldesman, Chairman Daniel J. Fneans Morris \1ei tman .- This thesis is a report on the analysis of family date. gathered to test the simple recessive hypothesis for the inabiHty to taste phenyl-thin-urea (P.T.C.). The Simple recessive hypothesis states that the inability of a minority of persons to taste high concentra­ tions of P.T.C. is due to the action of an autosomal recessive gene in the homozygous condition. The data consisted of the taste thresholds for P.T.C. of ;5 families, including parents and their children. )l'he" taste thresholds were determined by the well known Harris and Kalmus method which 2 employs a $eries of fou~teen dilutions of,P.T.C. in distilled water in which ~ach solution :i.1;l half a,s strong 'as the p~evious one. 'l'he threshold solution 'concentration at'which ~ach aubj~ct could taste " . was precisely determined by a sorting~est in which the subject was required to separate by tas,t€ cups containing,p.T.C. solution from cups containing distilled water. 1 ~ ~ • Some prev-ious experiments on the inheritance of the P.T.C. taote character have reported rasul ts which departed ~,significantly from the predictions of the simple recessive hypothesis when taste thresholds , ' were determi.ned by the,Harris and Kalmus technique. Some of these divergences may have been due to measurement error caused by dete­ rioration of the P.T.C. solutions over'time. In the present study precautions were taken to m.ix, store, and admi~ister the solutions under carefully controlled conditions" so as' to minimize the possi- . ~ ~ bility of errors in the threshold determination. 'The reaul ting taste thresho,ld data 'Were analyzed by two dif- '. ferent methods to determine if they, agreed with the predictions of the s~mple recessive hypothesis. The,first was Fisher's method which uses gene frequencies estimated from the parental sample a.nd Mendel- ian ra.tios to predict the number of families which (a) contain'a1l taster children and (b) contain at least, one non-taster child for both taster x taster and taster x non-taster ~atings. The second, was Smith's recessives estimation method which utilizes no gene fre- quencies. Smith's test uses Mendelian ratios to predict the exact 'number of non-taster ohildren in sibships' containing at least one non- taster child for both taster i ~a~ter and taster x non-taster matings. :5 Analysis of the 35 families by both~ethods showed that the data clearly agreed with the simple recessive hypothesis. The data were also examined to determine if the age and sex of the subjects affected the taste tr..resho1d for P.T.C. No such effects were found. The conclusions were drawn that (1) the pr~cautions taken in the preparation,.~ storage,. andad.ministrathm of th.e solutions reduced ' ..~.: I measurement error and (2.) the family da.ta at'ronglysupported the simple recessive hypothesis for non-tasting. Fut'..1re research designs should concern include both a larger sample of families and careful care of solutions. TO THE OFFICE OF GRADUATE STUDIESi 'rhe members of the Committe", approve t;he thesis of Sus~.n I. Wolf presented A~guat 20, 1913. / APPROVED: ~homas liewman, Head, Department of AnthrcpOlog:i; . DKvid T. Clark, Dean of Graduate Studies AUg'.lst 20, 1913 ,TABLE OF COlrrENTS PAGE v LIST OF TABLES. • • " • 1ft •• « .. ,. 4: ....... • • •• • • • • • LIST OF FIGURES • • • • • • • • • '.. • • • • • • • • • • • • vi CHAPTER I INTRODUCTION. • • • • • • • • • • " • • • • • s • 1 The Problem .. • " • • " .• • .. • • • • • • • • .. • ... 1 Historical Baokground • • " • • • • • • • • • • • 2 Crystal Studies Solution Studies Current Status of the Problem cO • .. 10 II J.1ETHODOLOGY .. ,. • " .,. • • . • '" • • • .• 13 The Sample. • . • ... • . • • .' • • • • • " .. 13 Size and Compositionol the Sample Seleotion of the Sample Families Bandomness of the ~.atings Procedure <$ • • • ., . .. - . • • • • • • • • • • • 16 The Test Situation The Test Solution Testing the Threshold Possible Misrepresentation of Taste Sensations The Color Code . Chang-lng Cups Summary of Testing Techniques Analysis of Data. .. .. ., . .,.. .. ". " • ·'·0 • • 25 Operational Definitions of Taster 'and Non-Taster AMethod of Analysis Not Used in the Present Paper . Two Methods of Analysis Used in the ,Present Paper CHAnER PAGE III RESULTS. • • • ~ • • • • .. • • .• • • • • • • • • • • •• ~1 e _ • • ~l Basic Data. .- . • • The Taste Threshold Dietribution Comparison of the Taste Threshold. Distribution by Age and Sex Estimation of the Gene Frequencies Phenotypic Constitution of the 35 Families !n:a..lyses.. • • . • • • e •. • • • • • • • • • • .. • •• 35 Randomness of the Matings Fisberls Hethod of Analysis Smith 1.$ Recessives E.stimation Method IV DISCUSSION, SUl1MARY, AND CONCLUSIONS. • .. • • • • • •• 44 Comparison of the Present Study with Sib-Pair and Other Family Studies. • • • • • • • • • • • •• 44 Sib-Pair Studies Errect~ of l1isclassificati.on Family-Studies Methodological and Theoretical Problems .. • • • 51 The Antimode as the Dividing Line Between - Taster and Non-tasters Tbe Issue of Incomplete Dominance Poasible Souroes of Ontogenetic Variation in the Expression.of the Taste Character • • • • • • • •• 55 The Influence of Age The Influence of .Sex The Influence of Smoking S~~ary of Data on Ontogenetic Variation Summary of the Results of the Present Study 0 • • • • Conolusion. • • • • • . .. .. LIST OF TABLES TABLE PAGE I Test for the Randomness o~ the !1atings • • • • • • • •• 16 II Test of Independe~ce for the Proportions of Male and Fema.le Tasters and:'Non-Ta.sters Among the Seventy Pa.l'ents .... ~, •. • • 0 • • • • • • • • • • •• 33 III Two-way Analysis of Variance.:. Ma.le/Female and Adul t/Child P.'1'.O. Taste f£hre:shl)lds • • . .... • • 34 IV Summary of the Phenotypic·Co1!lposit:l..onof the Thirty-five Families wi th'106 Children. • • • • ~ •• 36 , v Summary of tbeAnalysis or.'hhe Txt Families. • • • • • 39 VI SUUInaryof the Ana.lysisof the -TxT- Families. • • • •• 39 VII Summary of Analysis by Fi"sher'a Method . " . • • · . 40 VIII Smith's Va.riation of Fisherfs Method: Summary ••• • • 40 IX Observed and Expected Ntmbers of Non-Taster, Children in ~ x iF Families'with at Least One Non-Taster Child.... .. • • • • • • • .'. • • • • • 42 X Observed and Expected NUmbers of Non-Taster. Children in Tx t Families'W''ith at Least One Non-Taster Child. • • • • • • • .• • • • • •• 43 vi LIST OF F!GURES FIGURE PAGE 1 Ta.ste Threshold Distribution 'of the Entire Sample. • •• 32 ~ ~".f~ ~ -~, .i~. t~;~:1:~Jr~'.. , ~.~'., ~ ~:'£ ., .•.; CHAPTER, I , " INTRODUCTION I. THE P110BLEM 'In the study of human genetiCS, the precise mode of inheritance '0£ many traits defies elucidation b'ecause available methods of o1>ser- : '. v8.tion and measurement c!:'.nnotrecord 'the action of genes themselves. Inferences about the genotype of the individual must be made on the basis of observable phenotypic traits or trait complexes which may be , " far removed from'the site of gene action. ~ Considerable modification of. a genetic trait may be, introduced by epistasis and pleiotropy as vellas by the Plfluence of the ":iwironment.' 'L'hese complex ~nterac­ tiona may p!,oduce phenotypes ,which do not accurately reflect the geno- type. Single gene,polymorphisms constitute ail e~ception to this rule. .. ~ Such systems are simple enough to be compared with expectations de-- rived from the laws of classica.l Mendelian genetics." In mant, the best known polymorphisma Bre the blood groups, which are controlled by genes obeying l'1endel's laws verJ, precisely. ,.• ',' Since the early 1930' s the ability or inability to taste the chemical substance phenYI-thio-urea ·(P.~'.c.)~· ha.s be'en, considered an- other single gene polymorphism. During that time it was generally held that the inability of a minority of per~ons to taste high con­ centrations of P'.T.C. was due to the action of an autosomal recessive gene in the homozygous form." However, in the'1950 r s, \rlith the' intro­ duction of more refilled techniques of't,esting" this "simple recessive hypothesis" became suspect as an exple.nation f.pr the inheritance of the trait (Ha.rris and Kalmus, 1951; Das, 1956; D~s, 1958). II .• HISTORICAL BAGKGROl~ Castal Studies In 1931 Dr. A. L. Fox of the DuPont Laboratories discovered. that a few crystals of the P.T.C. placed on the back of the tongue pro- duced two very different reactions:. '(1) most persons reported tha.t , , the substance had a very strong bitter .',ta'ste, ·and (2) a minority cculd perc~ive no fla.vor a.t all (Fox, 1931). Fro.m this he concluded that " the abil~ty to taste the substance couldseg;~gate persons rege.r~lee8 of- age, sex, or race into classes--"tasters" and "non-tasters".