Sunday, 3 June 2012

Genetics all in a family: Marvellous are the functions of the genes

By Syed Akbar


"Ghar Jamai". The very word stirs up the masculine conscience of every man. 
A man generally do not like to be a "Ghar Jamai" (man moving over to wife's 
house after marriage) because he feels that it leads to subjugation of his 
"manly" respect and self-esteem.
Culturally and traditionally the concept of "Ghar Jamai" may have hurt the 
sentiments of the male species of Homo Sapiens, but geneticists say that this 
practice has little to do with the variation in the gene make-up of a 
population, at least in India.
World-wide the "Ghar Jamai" concept might have led to vast variations in the 
gene make-up of local populations because of the flow of male chromosomes 
from one locality and group to another. But as far as Indian populations are 
concerned, the traditional view of geneticists on this concept does not hold 
water.
The reason, anthropologists and geneticists, argue is that Indian populations 
are quite different from those living elsewhere in the world. This is because 
marriages in India, by and large, are based on caste, religion, language and 
regional considerations.
India, with its vast populations divided on caste, religion, linguistic and 
regional lines, is unique as far as genetic variation is concerned. No other 
nation in the world shows such genetic patterns as exhibited by the Indian 
people. The uniqueness of Indian populations is that they are mostly 
endogamous i.e. marriages are guided by cultural and traditional practices 
and are held within the given community, caste or group. The view held by 
geneticists world over thus far is that the gene flow chart in both patrilocality 
(man moving over to wife's place after marriage) and matrilocality (woman 
moving over to husband's place after marriage) are uniform the world over. 
But Indian scientists dispute this saying that it does not apply to Indians.
"The patterns of genetic variation in humans are not universal, but depend on 
local cultural practices," says Prof B Mohan Reddy of Indian Statistical 
Institute, Hyderabad.
In most human societies, women traditionally move to their husband's home 
after marriage, an these societies are thus "patrilocal", but in a few 
"matrilocal" societies, men move to their wife's home. These social customs 
are expected to influence the patterns of genetic variation.
They should lead to a localisation of  male-specific Y-chromosomal variants 
and wide dispersal of female-specific mitrochondrial DNA variants in 
patrilocal societies and vice versa in matrilocal societies.
These predicted patterns have indeed been observed  in previous studies of 
populations from Thailand.
Indian societies, however, are endogamous, so marriage should always take 
place within a population, and these different patterns of genetic variation 
should not build up.
The study carried out jointly by the Biological Anthropology Unit of ISI, the 
Centre for Cellular and Molecular Biology, Department of Anthropology, 
North Eastern Hill University, Shillong, GSF Hematologikum, Munchen, 
Germany, LV Prasad Eye Institute and Kallam Anji Reddy Molecular 
Genetics Laboratory, has analysed 10 patrilocal and five matrilocal Indian 
populations, and found that there is indeed little difference between the 
patrilocal and matrilocal societies. The patterns of genetic variation in 
humans are not universal, but depend on local cultural practices.
"The spatial instability of the impact of different cultural processes on the 
genetic variability has resulted in the lack of universality of the hypothesised 
pattern of greater Y-chromosome variation when compared to that of 
mitochondrial DNA among the patrilocal populations," the study observed.
The males posses Y-based sex genes while the females contribute 
mitochondrial genes. The mitochondrial genes are given by mothers to 
daughters while Y-chromosomes are passed on from fathers to sons.
The variability (or genetic distances) within a population (i.e. same caste, 
tribe, religion, region etc) in case of patrilocal concept is high for 
mitrocondrial genes. The variability will be lower between two or many 
populations in this case, because when woman moves the mitochondria also 
moves which reduces the genetic distances between various groups.
In case of matrilocal societies (Ghar Jamai) the Y-chromosome moves with 
the husband and this reduces variability between populations for "Y" and 
increase variability within the population.
"This was the evidence found in Thailand and other places. But this cannot 
be universal for all societies. In the Indian context, populations are highly 
endogamous. So the variability generally found in other countries is not 
observed in the Indian context," argues Vikrant Kumar, one of the 
researchers.
For populations bound by rigid endogamy rules with their boundaries 
absolutely impermeable, neither patrilocality nor matrilocality can make any 
difference to their genetic variability, be it Y-chromosome or mitochondrial 
DNA. This is so, because the gene movement is restricted to within a 
population, Prof Mohan Reddy pointed out.
The populations included in this study are Maram, Khynriam, Pnar, Bhoi and 
WarKhasi, the five matrilocal Khasi tribes of Meghalaya, and Asur, Bhumij, 
Kharia, Munda and Santhal, the five patrilocal Mundari tribes of Eastern 
India. To guage the consistency in the genetic patterns within broad regional 
or cultural context, the same set og genetic data were generated on the five 
Dravidian language-speaking patrilocal caste populations of Andhra Pradesh 
i.e. Akutota, Kapu, Panta, Pokanati, and Vanne and compared with the north-
Indian matrilocal tribes.
Blood samples from 636 individuals belonging to 15 populations were 
obtained for the study.

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