The marital or sexual relationship between two persons belonging to the same genre (family) is known as consanguinity marriage. This method is widely accepted in around one-fifth part of the world, i.e. Asia, North Africa, Switzerland, Middle East and some parts of China, Japan and India. Consanguinity does not depend upon the amount of DNA shared between two person's genome, it rather depend upon the number of reproductive process (meiosis) occurring between them. The first cousins share 1/8 of their genes inherited from their common ancestor, thus their progeny are homozygous in nature with about 2.4% variation occurring due to some external factors like, environment, geography, ethnics, etc.
Earlier, consanguineous marriage was performed between siblings, i.e. first cousins by the Egyptian Pharaohs to preserve their royal blood. Even now in some parts of the world like, UAE, India, such customs are prevalent. They believe that by doing so their culture, tradition and royalty will not be adulterated and the purity of the gene will be maintained. But this give rise to several serious problems like, genetic disorders, physical and mental malformation, deterioration of health, etc. The deficiency in the family is enhanced and succeeded further in the coming generations.
Genetic disorders are quite adamant in such type of consanguineous relationships. The risk of inheriting any autosomal recessive genetic disorder is quite high in the children of such parents. The offspring of consanguineous couples are at a greater risk of certain genetic disorders such as Retinitis Pigmentosa, Leber congenital amaurosis, Lawrence-Moon-Bardet-Biedl syndrome, Stargardt disease, Usher syndrome, etc. Even age related brain disorder like; Parkinson's is found to be consistent in such families. Consanguinity transmits genetic disorder prevalent in the family to their successors. If the complete family is not suffering from any type of genetic disorder then the chances of having genetic disorder to coming generations decreases and the rate of malformation and mortality increases in the children born from consanguineous relationship. In the case of marital relationship between first cousins, there is a risk factor of about 5% mortality and mental or physical dysfunction in early childhood.
A social cross sectional study was also conducted in the year 2003-2007 regarding this consanguinity marriage system. This ethically approved prospective study showed that some congenital malformations have a lower incidence rate. The prevalence of congenital heart related disorders is found to be approximately 0.008 to 0.004, neural tube defects (NTDs) is 0.01 to 6.67X10-4 and that of cleft lip is about 0.004 to 0.002. These demographic values suggest that consanguinity does play a negative role to the human health. The community should try to demolish the traditional, cultural and customary factors which are responsible for consanguinity. This system is leading to many biological damages and dysfunctions.
Whereas in some parts of the world, people are avoiding such nuptials. In northern part of India, people avoid the consanguineous marriages by looking at the 'Kundilis' for the patrilineal relationship between the probable bride and the groom. In USA and some other western countries consanguinity closer than the first cousins are legally unaccepted.
The marital relationship should be bonded between two persons with no blood relationship or who are not related to a common ancestor. The successors of common ancestor share some amount of similar genetic material. The siblings from the same parents share about 50% of the genetic material. The uncle and niece share 25 percent and the first cousins share 12.5 percent genetic material. The genetic disease, deficiency or disorder prevalent in the family, could easily get transferred from one generation to another in the case of consanguinity. The chances of genetic disorder are very rare among the offspring of the persons who are paired randomly, i.e. not associated with each other through blood (non-consanguinity).
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