68 Hefeditary Lrft handedness 



The main body uf data is somuwhat unsatisfactory in respect of the 

 absence of collateral histories; these are indispensable for complete 

 studies seeking evidence of Mendelian inheritance; however, the 

 abbreviated histories are still of the greatest value, and warrant careful 

 analysis and permanent record. 



Three remarkable five-generation discontinuous histories of heredi- 

 tary lefthandedness are included, charted in Figs. 1 to 3. Here the 

 absence of collateral histories and record of the total number of 

 individuals in the several childships is especially regrettable, and 

 precludes attempts at further analysis. 



Four histories of direct transmission are charted in Figs, i to 7. 

 Chart 6 is noteworthy in that all the affected individuals are males. 

 Chart 5 suggests recedence of the sinistrality factor, since the Icfthanded 

 individual of the last generation is the result of a double Icfthanded 

 mating. However, the three Icfthanded individuals of the preceding 

 generation contradict this general deduction, since the female parent 

 was presumably righthanded. Moreover, the fact that the mother had 

 also 3 nieces, 1 nephew, and 3 great-nieces who were Icfthanded suggests 

 almost equally cogently that in this family lefthandedness was dominant. 

 This particular history will be further discussed below in an attempt to 

 interpret apparent cases of dominant lefthandedness. 



The blanks include also eleven, in six of which only an uncle or an 

 aunt of the Icfthanded individual is known to be similarly affected, and 

 in five only a great-uncle or great-aunt. Several of these are charted 

 and discussed below (Figs. 69 — 74). 



Forty-eight blanks record lefthandedness in both parent and child. 

 The histories with more than one affected member in the fraternity are 

 charted in Figs. 8 to 1(1 This set includes only one instance of double 

 Icfthanded parentage (Fig. 16). The expected total frequency on 

 Mendelian assumptions is vitiated by the presence of one " normal." 

 In the other histories of this set, one of the parents is normal as respects 

 use of hand. On the assumption that the " normals " are hetcrozygotes 

 the majority of the charts fulfil Mendelian expectancy for RR x DR 

 crosses (Figs. 10, 11, 13, 9, and 1-5). Chart Fig. 8 suggests dominance 

 of the Icfthanded trait, as also to a lessor extent, in view of the limited 

 childships, charts Figs. 12 and 14. A strict Mendelian interpretation 

 of this group of charts (Figs. 8 to 16) involves the further assumptions 

 of degrees of bias to sinisterity and variation in relative hereditary 

 prepotency. An attempt will be made to .support the legitimacy or 

 plausibility of these assumptions below. 



