Added: 15 May 2018
Science behind Gotra (Genetics);
What is Gotra system?
Why do we have this ? Why do we consider this to decide marriages?
Why should sons carry the gotra of father, why not daughter?
How/why does gotra of a daughter change after she gets married ?
What is the logic ?
Infact this is an amazing genetic science we follow.
Let's see the science of genetics behind gotra systems.
The word GOTRA formed from two sanskrit words GAU (means cow) and Trahi (means shed).
Gotra means cowshed.
Gotra is like cowshed protecting a particular male lineage. We identify our male lineage / gotra by considering to be descendants of the 8 great Rishi (Sapta rishi + Bharadwaj rishi). All the other gotra evolved from these only.
Biologically, human body has 23 pairs of chromosomes (one from father and one from mother) on these 23 pairs, there is one pair called sex chromosomes which decides the gender of person.
During conception if the resultant cell is XX chromosomes then the child will be girl, if it is XY then it is boy.
In XY - X is from mother and Y is from father.
In this Y is unique and it doesn't mix. So in XY, Y will suppress the X and son will get Y chromosomes. Y is the only chromosome which gets passed down only between male lineage. (Father to Son and to Grandson).
Women never gets Y. Hence Y plays a crucial role in genetics in identifying the genealogy. Since women never get Y the Gotra of the woman is said to be of her husband.
They are 8 diff Y chromosomes from 8 Rishis. If we are from Same Gotra then it means we are from same root ancestor.
Marriages between same Gotra will increase the risk of causing genetic disorders as same Gotra Y chromosomes cannot have crossover and it will activate the defective cells.
If this continues, it will reduce the size and strength of Y chromosome which is crucial for the creation of male.
If no Y chromosome is present in this world, then it will cause males to become extinct.
So Gotra system is a method to avoid genetic disorders and attempt to protect Y chromosome.