Section 15 — Human Genetics 



that in a sample of mothers with sickle-cell 

 trait (Hb A Hb s ) the sex ration among their 

 children is normal whereas in the sample of 

 Hb A Hb A mothers, the sex ration was low. The 

 observed equilibrium values for sex ratio in this 

 population are very close to the calculated 

 equilibrium values based on the observed 

 frequency of the sickle-cell trait in adult males 

 and females. The relationship between sex ratio 

 of a population and level of malarial immunity 

 will be explored. 



15.16. Does there Occasionally Exist an Incom- 

 patibility of Mothers with Their Male Off- 

 springs? K. O. Renkonen (Helsinki, Finland). 



The known phenomena of incompatibility are 

 enhanced by repeated pregnancies or transplan- 

 tations. Accordingly, in a study of incompati- 

 bility of mothers with their male offsprings the 

 first question should be: how are the sex ratios 

 (m/f) of live births influenced by repeated 

 pregnancies. It is well-known that the sex ratio 

 is steadily decreasing by birth order. As such it is 

 not a sufficient argument for incompatibility, 

 because the primary sex ratio could also have 

 been decreasing by birth order. That would imply 

 a decrease also in the sex ratio of stillbirths by 

 birth order, but there is a remarkable increase 

 instead. 



If the decrease of the sex ratio by birth older 

 is due to incompatibility, it should be manifested 

 not only by repeated pregnancies but also by 

 repeated births of boys. The families that have 

 already got both boys and girls should then have 

 the highest sex ratio of the next child, if there is 

 only one boy among the precedent children ; 

 lower, if two boys were already born, and lowest, 

 if there were three of them. The observed 

 statistical data are in agreement with this 

 prediction. 



Let us suppose that some of the mothers in one 

 type of families are incompatible with their male 

 offsprings, but all are compatible in the other. 

 Then the birth interval to the next child should 

 be lengthened among the families including 

 incompatible mothers. The observed data 

 suggest that it is so. In addition, the lengthening 

 of the birth interval should be caused only by 

 those intervals terminating with a girl, just as it 

 is, for, if the birth interval is terminated with a 

 boy, the mother can hardly be incompatible. 

 In conclusion I should like to interpret the 

 statistical data to support the assumption of an 

 occasional incompatibility of mother with her 

 male offspring. 



15.17. Studies on Colour Blindness among the 

 Tribals and Non-tribals of Andhra Pradesh, 

 India. K. R. Dronamraju (Orissa, India) 

 and P. Meera Khan (Andhra Pradesh, 

 India). 



The Polavaram Agency area of Andhra 

 Pradesh in southeastern India has, according to 

 the 1961 census, a population of 22,461 non- 

 tribals and 23,810 tribals. The non-tribals are 

 largely Hindus, but there are a few Christians 

 and Muslims also. The tribals include Koya 

 Doras, Koya Kammaras, Musaras, Konda 

 Reddis, Konda Rajus, Sugalis and Pandava 

 Nayakas. Tests using Ishihara (1960) Plates, 

 showed that 6.5 per cent of 569 non-tribals and 

 2.5 per cent of 1155 tribals were colour blind. 

 1.5 per cent of non-tribals and 0.34 per cent of 

 tribals were Protans. The tribes in which one or 

 more colour blind men were discovered are 

 Koya Daras, Musaras, Konda Rajus and 

 Sugalis. The low frequency of colour blindness 

 found among these tribals is in general agreement 

 with that reported in Navajo Indians, Australian 

 aborigines, and some African tribes. The differ- 

 ence between the frequencies among the tribals 

 and non-tribals in Andhra Pradesh is highly 

 significant (X 2 = 16.40) and is explained as due 

 to the relaxation of selection against colour 

 blindness in civilized communities. 



15.18. The Incidence of Cuna Moon-Children. 



Clyde E. Keeler (Milledgeville, U.S.A.). 



The incidence of Cuna Indian Moon-child 

 albinos is more than 60 per 10,000 population, 

 being reduced from about 69 per 10,000 in 1925. 

 Stout's 1940 estimate of 47 per 10,000 is probably 

 in serious error. Our 1962 data suggest infanticide 

 is uncivilized towns and possibly selective inter- 

 breeding of heterozygotes in the town of Nar- 

 gana. Absolute population figures cannot be 

 obtained, due to census methods and unrecorded 

 absentees. Our figures show albinos to be less 

 viable than normals, in keeping with general 

 Cuna belief. Since albinos seldom reproduce, 

 the gene frequency in one generation without 

 mutation should have been reduced to 57 per 

 10,000, so there is evidence that mutation does 

 take place. It is estimated that about 398 mu- 

 tations per generation per 10,000 population are 

 added to the gene pool in order to provide the 

 5 new albino homozygotes per generation 

 necessary to keep the incidence at equilibrium. 

 Examination of our 1950, 1960 and 1962 data 

 all show Moon-child albinism to be due to a single 

 pair of recessive, Mendelian, mutant genes. 



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