Endogamy
Endogamy is the cultural practice of mating—usually in the form of marriage—within a specific social group, religious denomination, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close interpersonal relationships.
Endogamy is common in many cultures and ethnic groups.
Endogamy, as distinct from consanguinity, may result in transmission of genetic disorders, the so-called founder effect, within the relatively closed community.
Endogamy and Genetic Disorders
In 2009, a study reported a fascinating finding on why a small group of Indians were prone to cardiac failure at relatively young ages.
They found that the DNA of such individuals lacked 25 base-pairs in a gene crucial for the rhythmic beating of the heart (scientists call it a 25-base-pair deletion).
Intriguingly, this deletion was unique to the Indian population and, barring a few groups in Southeast Asia, was not found elsewhere.
They estimated that this deletion arose around 30,000 years ago, and affects roughly 4% of the Indian population today.
In a recent study researchers collected DNA from around 5,000 individuals, mainly people from across India, Pakistan, and Bangladesh. This cohort also contained DNA from some Malay, Tibetan, and other South-Asian communities.
Their study found stark genetic differences between people from different regions of the subcontinent.
While this is to be expected between different countries in the region, it was actually evident even at the level of smaller geographies within India.
It is a no-brainer that endogamous practices (including caste-based, region-based, and consanguineous marriages) in the subcontinent are responsible for such conserved genetic patterns at the community level.
In an ideal scenario, there would have been random mating in a population, leading to greater genetic diversity and lower frequency of disorder variants.
The study also highlighted a worrying trend in the Indian population.
Compared with a relatively outbred population, like that of Taiwan, the South Asian cohort – and within it, the South-Indian and Pakistani subgroups – showed a higher frequency of homozygous genotypes.
Humans typically have two copies of each gene.
When an individual has two copies of the same variant, it is called a homozygous genotype.
Most genetic variants linked to major disorders are recessive in nature and exert their effect only when present in two copies.
Having different variants – being heterozygous – is usually protective.
The South Indian and Pakistani subgroups were estimated to have a high degree of inbreeding, while the Bengali subgroup showed significantly lower inbreeding.
The reasons for this are unclear but could be cultural in nature.
At the same time, the three subgroups had 300-600-times higher levels of rare homozygous variants than what would have been predicted if the matings had been random.
The study indicated how our cultural aspects might need mending for the sake of population health.
This is obviously fraught with sensitivities owing to deep-rooted customs and biases.
But we must move away from the idea of genetic puritanism because it will be the simplest way to prevent major hereditary disorders.
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