Prevalence of Blood Group Trait among Scheduled Castes of Patna (Bihar)

INTRODUCTION

Study of genetic structure of populations is of great importance in knowing their adaptation as well as their ethnic relationship. Genetic variability is the common feature of many organisms. The modern human populations carry in their genes, the encoded history of remote past and earlier migration history. Human populations differ genetically in varying proportions of the alleles of various sets. Human biological variations are related to the ethnic and ecological background of the population. Genetic markers in human blood, particularly the blood groups of the individuals, are the simplest parameters in this regard because of their association with different disease (Bhasin and Walter, 2001). Literature is full of information suggesting better resistance or susceptibility of the individuals of a particular blood group to a particular disease. Not only this, some sort of incompatibility has been also reported to exist when spouses belong to one or the other blood group. The association of blood groups with different types of diseases has been established by many workers in the past (Waterhouse and Hogben, 1947; Boorman, 1950; Aird et al., 1953; Allan, 1953; Matsunaga, 1955; Vogel and Helmbold, 1972; Vogel, 1975; Mourant et al., 1978). The diseases of typhoid and paratyphoid as well as tuberculosis and sacoidosis, have high frequency among Rh-negatives (Mourant et al., 1978). Viral diseases also show in general a deficiency of Rh-positives, which is significant for mumps and viral meningitis (Pacirorkiewiscz, 1970). Duodenal ulceration also exhibits a significant association with Rh-groups (Mourant et al., 1978). Besides blood group based polymorphism, two well-known genetic traits that also affect the survival (adaptive) fitness of the individuals, are the sensitivity (or the blindness) to red-green colours (colour blindness) as well as to the bitter taste of phenylthiourea/ phenylthiocarbamide (PTC). From the distribution of colour-blindness in the different population groups of the world, Post (1962, 1971) and Pickford (1963) cited it to be the best trait for investigating ‗relaxed selection‘. This argument is based on the low rates of colour-blindness prevailing in primitive communities as compared with higher rates among civilized communities. Post (1962) was of the opinion that colour vision defects would be more damaging to primitive population since they have to depend upon game for their subsistence and in which full vision power selection operating in them. Dutta (1966), compiling the data of Indian population, found lower prevalence of colour blindness among tribals them advanced Hindus and thus confirmed the Post‘s hypothesis of relaxed selection. Kapoor et al. (1983) categorized the various studies available on the population of India and observed lower incidence of colour blindness among groups with primitive cultures; similar findings have been earlier reported by Malhotra et al. (1974) and Malhotra (1978a). Kapoor et al. (1983) concluded that the differences in these categories for the incidence of colour blindness indicate selection relaxation in settled communities. Selection pressure tends to eliminate colour blind individuals from primitive populations whereas the habitats of advanced populations provide a protected environment for the colour blind gene. Deka (1977) and Deka et al. (1977) also observed low frequencies of colour blindness among Scheduled tribes, followed by Scheduled castes, whereas the frequency was quite high among the caste groups. Naidu (1978) observed low frequency of colour blindness among primitive tribals of Andhra Pradesh ccompared to advanced non-tribals. Almost similar pattern has also been observed from different zones of India (Bhasin et al., 1994). These observations perfectly fit into the hypothesis proposed by Post (1962). Adam et al. (1967) and Adam (1969, 1985, 1986), however, did not fully support the Post‘s hypothesis of relaxed selection, yet the possibility of relaxation of selection was not ruled out. They found high frequency of colour vision defects among some of tribal populations of India. Although the high frequency of inbreeding and settled agricultural economy are the reasons given to explain the prevalent high frequency of colour blindness in these populations, the validity of the theory of relaxed selection will have to be substantiated by further studies and more quantitative data. Ability to taste PTC, like colour blindness, also exhibits a strong dimorphism in human population. A number of studies, showing a strong association of this polymorphism with the activity of thyroid (Harris and Kalmus, 1949 b) have revealed the high occurrence of adenomatous goiter among non-tasters (Kitchin et al., 1959; Azevedo et al., 1965). In addition to this, it was found that athyreotic cretins were significantly more likely to be non-tasters than normal controls (Shepard and Gartler, 1960; Frazer, 1961). Non-tasters have even more susceptibility to dental caries (Chung et al., 1964) and diabetes mellitus (Terry, 1950). Reports are also available regarding the association of non-tasters with other diseases (Saldanha, 1956; Beiguelman 1964; Brachtel and Walter, 1974; Mourao and Salzano, 1978), detailed work would however be needed to advance further comments in this direction. Needless to say that on the basis of aforesaid parameters, populations can be compared among each other for their survival (adaptive) fitness. Bhasin and Walter, 2001). It is well known that populations belonging to different races have different values for the above mentioned parameters. On the other hand, those who are living in the same locality (indigenous) and seemingly closer to the each other, may not show differences on these account. Populations that have arisen by fusion will exhibit perceptible differences among themselves, and those arising out of fission mechanism will fail to do so. The aim of the present work was therefore to study the Blood Group characteristics of the four predominant Scheduled Castes (Mendelian populations) of Patna district (Bihar), namely Dusadhs, Chamars, Pasis & Mushars. This will help as to evaluate inter-population variations among them in terms to ascertain their probable mode of origin, by fusion or fission.

The locality of the present survey, the District of Patna in the State of Bihar (India), is one of the oldest continuously inhabitated regions in the world. The modern city of Patna is situated on the southern bank of the Holy River Ganga. The city is approximately 35 km long and 16-18 km wide . About 15.48 percent (7.30 lakh) of the total population in the district is represented by Scheduled Castes, the second highest population of Scheduled castes at the district level in the State after Gaya. According to the Census Report (2001), the four predominant Scheduled Castes (in term of population) in the district of Patna are Dusadh (2.77 lakh), Chamar (1.99 lakh), Pasi (0.93 lakh) and Musahar (0.93 lakh) which together form more than 90 percent 0f the total Scheduled Caste population. A preliminary survey was conducted in different villages/urban mohallas in the various Developmental Blocks of Patna district (Bihar) to locate the presence of four dominant Scheduled Castes (the Dusadh, the Chamar, the Pasi and the Musahar communities) residing therein. The villages/mohallas thus identified were numbered and 48 of them (in 17 Blocks) were randomly selected for intensive survey and collection of data on the two parameters of study, the quantification of the reproductive performances of the four predominant Scheduled caste populations as well as the analysis of the prevalence of certain biogenetic (Mendelian) traits in them. More than 1000 pesons, each of Dusadh and Pasi communities, were surveyed while the number of persons surveyed in each of Chamar and Musahars populations remained limited to 700-800

The term ―Scheduled castes‖ stands for the population of such people from among the ―Depressed classes‖ who have been explicitly recognized by the Constitution of India as per Presidential Orders issued under the provisions of Articles 341 of the Constitution. Ninety percent of the Secheduled Castes are rural based and provide substantial support to Indian agriculture. The occupational structure of the Scheduled Caste work force is, by and large, made up of the following components: 1. Landless agricultural labourers, 2. Cultivators with small holdings, 3. Small commodity in producers or artisans, and 4. Workers in industries related with their traditional crafts (such as leather tanning, shoe making etc.) Among the total Scheduled Caste population in Bihar (13 million), the Chamars have the highest population (4.09 million). The Dusadh community follows them closely (4.02 million). According to the census, there are 23 such caste groups in Bihar that are considered under the Scheduled Caste category (Census of India, 2001). Here it becomes necessary to state that if we talk in context of the Education &Socio-economic status of the four talked castes in Patna. ―Dusad(s0)‖ are at the top of ladder among these four while ―Mushar(s0‖ are at the lowest.

Discovery of ABO blood group by Karl Landsteiner (1900) was a milestone in the history of immunohaematology. Very soon a fourth group viz. AB was discovered by Decastello and Sturli (1902). Grouping of human blood into four categories, viz. A, B, AB and O therefore depends upon the presence of A or B or the both blood group antigens or their complete absence in their red blood cells. Landsteiner also initiated the study of the simply inherited polymorphic traits in man on the basis of ABO blood groups. The inheritance of blood group was suggested by Epstein and Ottenberg in 1908. In 1911, Von Dungern and Hirszfeld established the Mendelian Pattern of their inheritance. In 1924, Bernstein determined the mechanism of inheritance of all the four blood groups of ABO system which were shown to be inherited as Mendelian characters by means of three alleles, i.e., IA, IB, and IO of a single gene. The ABO locus is assigned to the distal dominance upon each other. The three alleles in various combinations form four different phenotypic groups which are A (IAIA or IAIO), B (IBIB or IB IO), AB (IAIB) and O (IOIO).

Door-to-door survey was carried out to determine the blood-group frequency among the individuals of all the four populations. The test, based on haemagglutination reaction, was performed by the process of slide-agglutination method (Bhasin and Chahal, 1996; Dacie and Lewis, 2001) with the help of monoclonal IgM antibodies (SpanClone, Span Diagnostics Ltd., Surat, India). Human RBCs possessing A and/or B antigen will agglutinate with the corresponding antibody (anti-sera). Two circles were marked (as A and B) on a clean slide where one drop of corresponding anti-serum was placed (i.e., antisera A at circle marked A and antisera B at circle marked B). One drop of fresh blood was placed on each of the marked area after pricking a left hand finger of the subject by a lancet (Amkay Products Pvt. Ltd., Vasai, Maharashtra) sterilized needle. Separate applicator sticks were used to mix blood with antisera and the slide was tilted back and forth for 2 minutes. Agglutination of RBCs with an antiserum indicated the presence of the corresponding antigen. Similarly, absence of agglutination of RBCs with an antiserum indicated the absence of the corresponding antigen. Results were analyzed within 2 minutes, as drying of the reaction mixture at the periphery may be misinterpreted as agglutination. Validity of antisera was checked at interval with known blood groups. The frequencies of three alleles (IA, IB, IO) were calculated by Hardy-Weinberg principle of genetic equilibrium using Bernstein‘s correlation (Strickberger, 1985).

All the four populations have different patterns of the incidence of various blood groups in them. Among the Pasis, the group ‗A‘ is most prevalent in both the sexes (37.29%). The next most common group in them is ‗B‘ (24.23%) to be followed by ‗O‘ (21.96%) and ‗AB‘ (16.57%). High frequency of Dusadhs, group ‗B‘ is most frequent in both the sexes (34.11%). The next in distribution are groups ‗A‘ (24.73%) and ‗O‘ (21.14%), which are more or less of the same magnitude. The least common group in this population is AB (17.32%). Group ‗B‘ is also frequent among the Sansis, a tribal caste of eastern Punjab (Sindhu et al., 1980). Highest frequency of ‗B‘ group is also reported in a tribal group (Pradhan) of Andhra Predesh (Pingle et al., 1981). Among the Chamars, there is almost similar incidence of groups ‗A‘ and ‗AB‘ (27.00% and 27.14% respectively). Group ‗O‘ and ‗B‘ in their own turn are again almost equal in their distribution (24.00% and 21.86% respectively). Almost similar distribution of group ‗O‘ and ‗B‘ has been reported in the Tibetans of Darjeeling (Singh et al., 1974). Among the Musahars, the group ‗O‘ is most frequent (37.20%) in both sexes. Group ‗A‘ and ‗B‘ come next to it and have almost a similar frequency (24.71% and 23.38% respectively). The group ‗AB‘ is least frequent (14.71%). High frequency of the group ‗O‘ followed by the ‗B‘ group is also evident among the Naga Vamsams of costal Andhra Pradesh (Venkateshwara et al., 1981) Similar results have also been found in some Iraqi populations (Al-Rubeai, 1975). Group ‗AB‘ therefore appears to be comparatively least frequent in almost all the four populations. Low frequency of the ‗AB‘ group is also reported among the Sansis of Punjab (Sindhu et al., 1980), in some Iraqi populations (Al-Rubeai et al., 1975) as well as in some Japanese populations (Fujita et al., 1978). The incidence of the four blood groups in the two sexes of each of the four populations is almost equal. The χ2 value between the two sexes calculated for this porpose (at 5% level of probability and 3 degree of freedom) appears to be quite insignificant (2.67 among the Dusadhs, 4.24 among the Chamars, 2.80 among the Pasis and 2.42 among the Musahars). The frequency of IO allele alone is more than 60% among the Musahars and more than 45% among the remaining three populations. The IB allele is approximately 30% among the Dusadhs and Chamars, and more than 20% among the Pasis and the Musahars. The IA allele frequency is higher among the Pasis (30%) and 17 to 22% among the Dusadhs, Chamars and Musahars. These differences in the gene frequencies have also been found among Kanet (Scheduled Tribes) and Koli (Scheduled Caste) of Kinnar district of Himachal Pradesh which clearly indicate biological distinct in the local populations (Papiha et al., 1980). On the basis of this allele frequency, the expected number of the individuals of the four blood groups was calculated using Hardy-Weinberg equations, and compared with the observed values obtained during the survey. The χ2- values obtained during such comparison were indicative of significant differences in each of the four populations. It means that none of the populations is the state of genetic equilibrium for this trait and so the individuals of The four populations were thereafter compared among themselves for the incidence of the four blood groups in them. It was found that all the four populations differed significantly with each other on this account. Significant differences between populations have been reported among nine endogamous groups of Kumbhars from Maharastra (Dutta et al., 1976). Nentsi tribal populations from North-Western Siberia also differ from each other in the distribution of ABO blood group system (Sukernik et al., 1979). Nevertheless, significant differences within a caste spatially separated from each other have been found as reported among Kaibartas of upper and lower Assam (Sen Gupta and Sarthak, 1979).

On the basis of the presence or absence of Rh antigen, the whole human population has also been divided into Rh+ve and Rh-ve groups. The first human blood found to lack all known antigens, Rh-null was found by Vos et al. (1961). Initially the genetic mechanism of the Rh-system seemed to be governed by a single pair of alleles, R and r, as postulated to account for the difference between Rh+ve and Rh-ve individuals. Wiener (1970) developed a hypothesis based upon a series of multiple alleles. According to Race and Fisher (1948), three pairs of gene are involved in the production of Rh antigen that are not allele but are located near each other on the same chromosome. The dominant form of these genes is represented by C, D and E, and its recessive form by c, d and e. A person is classified Rh+ve on the basis of the presence of any of the three dominant alleles, and the presence of all the three recessive alleles make the person Rh-ve. Later, Rosenfield et al. (1973) developed a new Rh notation system to be represented by only two alleles, D and d.

A test for Rh (D) incompatibility was performed by the process of slide agglutination method with the help of SpanClone anti-D (Rho) monoclonal IgM antisera (Span Diagnostics Ltd., Surat, India). One drop of anti-D was dispensed on a clean dry slide, and a drop of blood was then added to it, mixed well with applicator stick and the slide was tilted back and forth for 2 minutes. If agglutination resulted, D antigen was present on the test RBCs and the blood was assigned Rh(+ve). No agglutination with anti-D antiserum indicated the absence of D-antigen, the blood group being Rh(-). Agglutination of erythrocytes therefore indicated incompatibility, whereas even distribution of erythrocytes indicated no reaction. Frequencies of

The incidence of Rh-ve subjects in all the four populations is slightly higher than the range known for Indian populations. It is comparatively higher among the Dusadhs (5.62%) with decreasing magnitude among the Chamars (5.29%), the Musahars (4.41%) and the Pasis (3.71%). Though slight inter-sex variations in the frequency of Rh-ve persons were observed within each population except Musahars, they were never statistically significant. Such high value is not unique for these populations alone, because Pingle et al., (1981) have found that in Rajgonds, a tribal group of Andhra Pradesh, it is 6.18%, and as high as 10 to 17%among the Sarswat Brahmins in Western India (Bhatia et al., 1976). High value of Rh-ve subjects is not only restricted in India, rather it is found in populations of other countries too; 8.31% in some Iraqi populations (Al-Rubeai, 1975), 7.37% in some Japnease population (Fujita et al., 1978) and 4.5% in Basrah, Iraq (Islam. Sukat and Islam Mohamad Khan, 1978). The frequency of dominant (D) and recessive (d) alleles shows a similar pattern of their incidence in all the four popualations. Consequently, the expected frequency of individuals homozygous (DD) for the dominant allele is very high to be followed by heterozygous recessive (dd) ones. All the four populations, except between the Pasis and the Dusashs, other in the incidence of this trait among themselves.

Based on the above collected data & observations made we conclude that 1. All the populations show different patterns of the incidence of ABO blood groups in them. The Group ‗A‘ is the most prevalent (37.22%) among the Pasis in both the sexes. Group ‗B‘ is the most frequent (34.11%) in both the sexes of Dusadhs. Among the Chamars, there is more or less a similar incidence of group ‗A‘ and ‗AB‘ (each 27%). Group ‗O‘ is most abundant among the Musahars (37.20%). 2. The frequency of IO allele alone is more than 60% among the Musahars and more than 45% among the remaining three populations. The IB¬ alleale is approximately 30% among the Dusadhs and the Chamars, and is more than 20% among the Pasis and the Musahars. The frequency of IA allele is higher among the Pasis (30%) and 17% to 23% among the remaining three populations. 5.62% (among the Dusadhs). On the basis of incidence of these genetic traits, G2 of Sanghvi (1953) was calculated to quantify the differences between pairs of population to estimate genetic distance between/among different populations. The value obtained suggests that the four populations are almost equidistant (G2 = 7.97 to 12.50) from each other, and appear at four vertices of a quadri-lateral structure. Their inter-populational differences are so large that they failed to form any cluster. Figure 1 illustrates the Frequency of ABO Blood groups, while its illustration caste wise in shown in Figure 2. Frequency (%) of ABO blood group allele (IA, IB and IO) is demonstrated by Figure 3 and its caste-wise illustration in Figure 4. Frequency (%) distribution of subjects of Rh(-ve) Blood group is shown by Figure 5. Figure 6 exhibits the frequency (%) of D(p) and d (q) allels in the populations. All the talked above, four Scheduled Caste populations are completely different from each other. They have perhaps neither evolved by fusion or by fission in the near past, and hence their inclusion in the list of Scheduled Castes has no any biological basis.

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Genetics Laboratory, Department of Zoology, Patna University, Patna 800005, India manojvibhakar@gmail.com