why everyones dna is not the same.?

humans have originated by evolving and adapting to environment.but the whole human race started from a women and men by reproduction in any stage.we know:a fathers or mothers dna matches with his or her childrens dna.

then this would have happened:     parents
                                                                  to
                                                                 child 1      child 2
                                                                      to                to       child 5 and child 6
                                                  child3               child4  
now as we see
parent gave birth two child and so the two childs dna is same.then the child 1 gave birth two child 3 and 4.as child 3 and 4 s dna is same to child 1  then it should be same to child 2.and so the dna of child 3 and 4 and 5 and 6 will match.so in this way when family keeps changing the dna will match with everyone.so everyones dna would match now.but now it does not match why?
it may sound stupid but i am a student of 13 years and so i dont know about it much.thanks for viewing and further answering   

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The first man and first woman have different DNA. Little differences like hair and eye color, how tall they are, facial structure and so on. But there are many genes that control all these things. With each new generation there is a possibility for environmental factors to cause a mutation in one of the genes. The children are not perfect matches to the parents. They are a match as far as specific DNA markers are concerned. Markers that are specific to the mother and markers that are specific to the father. So the first 2 children are half there mother and half there father. Now those children marry and have children. The 3rd generation is now 1/4 there grandfather and 1/4 there grandmother. As the generations continue they drift further and further from matching the DNA markers of the first generation. But some markers never change and can be traced back to what is known as Scientific Adam and Scientific Eve. Science's concept of the first official human male and female. Markers that over 90% of the world's population have. If you have access to Netflix then look for a documentary about scientific Adam.

DNA is a very complex subject.
argha halder (author)  mpilchfamily4 years ago
thanks for the answer!
blkhawk4 years ago

Nature is absolutely amazing when it comes to reproduction. There is a system specifically designed to make children different.

A person has a set of chromosomes. Each chromosome contains two halves that join in the middle so they look like an "X." All that a chromosome is, by the way, is two very tightly coiled strands of DNA (deoxyribonucleic acid).

The two halves of each chromosome come from the two parents. One half of the "X" in each chromosome comes from the mother, and the other half comes from the father. The two halves are bonded together at the middle of the "X." Each half of the "X" contains a complete set of genes, so each chromosome has two copies of every gene -- the "dominant" gene of the two is the one that is expressed.

A sperm and an egg meet to create a new person. The sperm carries one half of the new person's ultimate chromosomes, and the egg contains the other half.

The question then comes down to, "Where does the DNA in the sperm and the egg come from?" Every cell in the father contains a complete set of X-shaped chromosomes that are exactly alike. Same for the mother. The father's chromosomes came from his mother and father, and the mother's from her mother and father. To make a sperm cell, only one half of the X is contributed. But which half? This is where nature does the especially amazing part. When forming sperm cells, the father's body randomly chooses genes from the two halves of the father's chromosomes. This means that every sperm cell contains a random mix of the father's parents' genes. The same thing happens when forming eggs. Therefore, each child that a couple produces is a random mix of the four grandparents' genes.

"How can children from the same parents look so different?"  01 April 2000.  HowStuffWorks.com. <http://science.howstuffworks.com/life/genetic/question92.htm>  26 July 2013.
the mitochondria DNA will nearly be the same from mother to child. But regular DNA will not be the same to either parent because of recombination of the genes.
rickharris4 years ago
In many essential ways it is - We all have 2 legs, 2 arms 2 eyes and 2 ears etc.

BUT the small difference are what make us individual. In general for most of us these difference are random and te evidence of evolution/mutation.

If the difference is large then in the past the person wouldn't be viable. Medical science can help many such people these days to live long and more comfortable lives so in some case these mutations stay in the "system" evidenced by what we call genetic conditions which can be passed onto our children.

Small changes like hair colour or eye colour aren't likely to be destructive.