Ajeet Jaiswal 79 ISSN 0975 5942 Vol.IV(1), Jan-June 2012, pp.79-89 Visit: http://www.isapsindia.org/apjss/index.html International Society for Asia-Pacific Studies (ISAPS), www.isapsindia.org Taste Sensitivity to Phenylthiocarbamide (PTC) and Incidence of Colour Blindness among the Jats and Brahmins of District Rohtak, Haryana Ajeet Jaiswal Assistant Professor, Department of Anthropology, Pondicherry University, Puducherry- 605014, India Email: rpgajeet@gmail.com Abstract Phenylthiocarbamide (PTC), divide human population into two groups, i.e. Tasters and Non-Tasters. PTC taste sensitivity by using the technique of Harris and Kalmus in 146 Jats and 138 Brahmin from Dist. Rohtak, Haryana reveals bimodal distribution of tasters and non-tasters; the incidence of tasters being 71.91% for Jats and 78.98% for Brahmans. There is a non-significant difference in their ability to taste PTC among Jats and Brahmans. Colour blindness was tested for colour vision with the help of Ishihara isochromatic colour plates. The percentage of incidence of colour blindness among Brahmin has been found to be 2.9% while in the Jats it is 2.7%. Keywords: Phenylthiocarbamide (P.T.C.), Red Green colour deficiency, Taster, Non-taster.
Ajeet Jaiswal 80 Introduction Phenylthiocarbamide: Phenylthiocarbamide as known PTC or phenylthiourea is a chemical compound that is made up of elements: carbon, hydrogen, nitrogen and sulphur. Based on the ability to taste Phenylthiourea (PTC), human population can be divided into two groups, (a) Tasters and (b) Non-Tasters. Variation in the ability to taste the synthetic compound phenylthiocarbamide was first recognised in the early 1930s, when A. J. Fox discovered the polymorphism in himself and a coworker, organic chemist C. R. Noller (Fox, 1932). The inability of some individuals to taste PTC was found to segregate in a nearly Mendelian recessive manner (Blakeslee, 1932), and subsequent studies went on to estimate the frequency of presumed Taster and Non-taster alleles in hundreds of populations worldwide (Guo and Reed 2001; Bhasin, 2009). Taste perception phenomenon presents an excellent opportunity to the population geneticists and anthropologists for the study of human variability. Besides its importance in genetic and anthropological studies, PTC taste sensitivity has also been shown to be important in food selection, which may affect individual metabolism and physiology. The ability to taste PTC or not has also been reported to show relationships with some diseases like diabetes, eye diseases, thyroid disorders, gastrointestinal ulcers and susceptibility to infectious disease. ABO and Rh blood groups are the most studied blood groups (Alimba et.al, 2010). PTC has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the tastes. The ability to taste PTC is a dominant genetic trait and the taste to determine PTC sensitivity is one of the most commonly used genetic traits on human.
Ajeet Jaiswal 81 Figure.1. Structure of the Human Tongue, Taste Buds Gustatory Cells, Nerves and Bitter Taste Receptors (Woodings, 2006). Colour Blindness Colour blindness is the decreased ability to perceive differences between some of the colours that others can distinguish. It is most often of genetic nature, but may also occur because of some eye, nerve, or brain damage, or exposure to certain chemicals. The English chemist John Dalton published the first scientific paper on this subject in 1798, Extraordinary facts relating to the vision of colours after the realization of his own colour blindness. Because of Dalton's work, the condition was often called Daltonism, although this term is now used for a type of colour blindness called Deuteranopia (Dalton, 1798). Colour blindness is usually classed as a mild disability, but in certain situations, colour blind individuals have an advantage over those with normal colour vision. There are some studies which conclude that colour blind individuals are better at penetrating certain colour camouflages and it has been suggested that this may be the evolutionary explanation for the surprisingly
Ajeet Jaiswal 82 high frequency of congenital red green colour blindness (Morhan, 1992). Post (1962) observed the frequency of colour blindness is less among the hunting and gatherers community which was supported by Pickford (1963). Later Dutta (1966), Mahapatra and Das, ( 1971), Kapoor et al. (1983), Morhan, (1992), Bhasin and Walter (2001); Bhasin (2009), Yumnam and Kapoor (2011) used Post's hypothesis to study various ethnic groups from India. In the present paper an attempt has been made to study the PTC and colour blindness among the Jats and Brahmins of District. Rohtak, Haryana. Materials and Method The data for the two polymorphic system i.e. PTC taste sensitivity and colour vision deficiency were collected from the Sampla village of District Rohtak, Haryana. The study was carried out in the year Dec 2002- Jan 2003. The subjects consist of both the sexes, which were taken from various primary and secondary schools situated in the Sampla region of District Rohtak. 146 Jats (78 males and 68 females) and 138 Brahmins (82 males and 56 females) in the age group of 10 to 60 year have been tested for their ability to taste PTC. For PTC taste sensitivity, serial dilution method was used by following the technique of Harris and Kalmus (1949) with the modification (Seth, 1961). Care was taken to avoid the close blood relation from being included in the sample. Same numbers of individual were tested for red green colour deficiency with the help of Ishihara isochromatic colour plates (Ishihara Charts, 1984) in a room with a sufficient day light. This test was conducted in day light in a room avoiding direct sunlight. Results and Discussion The percentage and gene frequency of tasters and non-tasters have been given in table 1. Among the Jats, the tasters are 71.91% while non-tasters are 28.09% and the gene frequency of non-tasters is 0.5299. In the Brahmins the percentage of tasters are 78.98% and non-tasters are 21.02 % and gene frequency of non-tasters is 0.4584.
Ajeet Jaiswal 83 In the table 2 Mean, S.D. and D/S value are presented. The mean value of tasters and non-tasters among Jats has been found to be 9.0095 and 1.2165 respectively, while in Brahmins the mean value of taster is 9.7156 and for non-taster it is 1.5517. The D/S index of Penrose (Penrose, 1952) was used to determine the bi-modality of the distribution. It has been observed that the D/S value for Jats and Brahmins has been found to be higher which confirms bimodality of the distribution. Brahmins and Jats show statistically nonsignificant differences for tasting ability. The gene frequency of non-tasters in Jats and Brahmins are 52.99% and 45.84%, respectively (Table 1) and it appear that the high percentage of non-tasters gene is due to the low amount of Mongoloid element in this region (Tiwari and Kapoor, 1984; Kotal, 1999; Kumar and Kapoor, 2003; Jaiswal and Upadhaya, 2011). Table 3 shows the percentage of incidence of colour blindness in two caste groups. Among the Jats males, the percentage of colour blindness has been found to be 5.1% whereas it is 4.9% in Brahmins males. All the females in both the groups are normal. The above genetic encodings lead us directly to the inheritance pattern. This will also show us on a glance, why there are more men suffering from colour blindness than women. The diagram shows the inheritance pattern of red-green colour blindness, which is by far the most common type of colour vision deficiency. As one can see, this is a disorder which is passed on from a grandfather to his grandson, whereas the mother is only a carrier of it. A carrier is not affected because the trait is recessive. This causes much more men to be red-green colourblind, and even more women to be carriers of this colour vision deficiency. One can also learn from this diagram, that a woman can only be red-green colour-blind if both of her parents are at least carrying the disease encoded in their genes (Shevell, 2003; Jaiswal and Upadhaya, 2011).
Ajeet Jaiswal 84 Figure.2. Red-Green Colour Blindness Inheritance Pattern About 8 percent of males, but only 0.5 percent of females, are colour blind in some way or another, whether it is one colour, a colour combination, or another mutation. The reason males are at a greater risk of inheriting an X linked mutation is because males only have one X chromosome (XY, with the Y chromosome being significantly shorter than the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one which carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome which carries the mutation. If 5% of variants of a given gene are defective, the probability of a single copy being defective is 5%, but the probability that two copies are both defective is 0.05 0.05 = 0.0025, or just 0.25% (Sharpe, 1999; Jaiswal and Upadhaya, 2011). When compared with the other population it is observed that the Brahmins of Sampla nagar shows non-significant differences with the Jats. Some higher caste of the Himalayan region like Rajput of Kulu, Brahman of Shimla, Rajput and Brahman of Garhwal also show the nonsignificant differences with Brahmins of Sampla nagar with reference to the tasting higher
Ajeet Jaiswal 85 caste of the Himalayan region like Rajput of Kulu, Brahman of Shimla, Rajput and Brahman of Garhwal also show the nonsignificant differences with Brahmins of Sampla nagar with reference to the tasting ability to PTC. Dogra of Tawi valley, Rajput of Kumaon, Brahman of Kumaon show significant differences with the Kolis (Kapoor, and Seth, (1981); Tiwari and Kapoor, (1984); Kumar and Kapoor, (2003); Bhasin (2009); Jaiswal and Upadhaya, (2011). The Jats show non-significant differences with Dogra of Tawi valley, Rajput of Kulu, Brahman of Simla and Rajput of Simla whereas Brahman of Bilaspur, Rajput of Bilaspur, Rajput of Kumaon show the significant difference with the Chamar for PTC tasting ability (Bhasin, and Walter, 2001). Most of the Eastern Himalayan populations show a low frequency of non-tasters gene. There is nothing unusual about these frequencies since Mongoloid populations are characterized by a low frequency of non-taster gene (Tiwari and Kapoor, (1984); Kotal, (1999); Kumar and Kapoor, (2003); Jaiswal and Upadhaya, (2010). When we move from the Eastern Himalayas to Western Himalayas the non-taster-gene frequency shows the increasing trend. From the result it has been observed that, in the present study the t is 52.99%, which is quite high and in the Brahman the gene percentage of t is 45.84% which is also high. So both the caste groups fall in the range of high non-tasters gene frequency of the Western Himalayas. As we move from the Eastern Himalayas to Western Himalayas the relative Mongoloid strain decreases with increases in the non-taster gene frequency. In the present populations the non-taster gene frequency is quite high and in both populations, which is native of Western Himalayas, have less Mongoloid characteristics and high non-taster gene frequency and high percentage of incidence of colour blindness.
Ajeet Jaiswal 86 Footnotes A study of taste sensitivity of P.T.C. and colour blindness among the Jats and Brahmins of Sampla of Rohtak district, Haryana shows that the t gene frequency was found to be 0.4701 and 0.5416 respectively in the total population, and that of colourblindness 2.9% and 2.7% among the males of Brahmins and Jats respectively. The results have been compared with the populations of Himalayan region of India. The trait of colour blindness among the populations of Himalayan region has been looked into, in view of the selection relaxation hypothesis. Acknowledgment The author is thankful to people of district Rohtak, Haryana for their cooperation. Author is especially grateful for the assistance and encouragement of my Prof. A.K. Kapoor and Prof. Satwanti Kapoor for their help during research. Author is also thankful to Deparment of Anthropology, University of Delhi for giving me all the instrumental assistance to carry out the present work.
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Ajeet Jaiswal 89 Tables Table 1: Percentage and Gene frequency of Taster and Non taster among Jats and Brahmins castes of Haryana S.No. Population Sample Taster Non taster Percentage Taster Non taster Gene frequency Taster Non taster 1. Jats 146 105 41 71.91 28.09 0.4701 0.5299 2. Brahmins 138 109 29 78.98 21.02 0.5416 0.4584 Table 2: Mean, Standard deviation (S.D.) and D/S value among Jats and Brahmins castes of Haryana. S.No Population Taster (M1) Mean Non taster (M2) Taster (S1) S.D Non taster (S2) D/S 1. Jats 9.0095 1.2163 2.0541 1.2398 4.73 2. Brahmins 9.7156 1.5517 1.9634 1.6313 4.54 D = M1 -M2 S = (S1 + S2) / 2 Table 3: Percentage of Incidence of Colourblindness among Jats and Brahmins castes of Haryana. Normal Colourblind S.No Population Sex No. tasted Number % Number % 1. Jats Male 78 74 94.1 4 2. Jats Female 68 68 100 0 5.1 Total 146 142 97.3 4 2.7 3. Brahmins Male 82 78 95.1 4 4. Brahmins Female 56 56 100 0 4.9 Total 138 134 97.1 4 2.9