Why are genetic disorders uncommon, when genetic recombination (crossing over) happens at every fertilization?

Question

my doubt is this: suppose there is a DNA sequence A1 B1 ... Z1 which is the rule to make some protein.During fertilization, when genetic recombination (or crossing over) happens, we end up with the sequence A1 B1 C2 ... Z2. wouldn't this result in a defective genetic sequence and there by a genetic disorder? If this is so then every time you have genetic recombination, isn't there a high probability that we end up with a defective gene?

Answer 1

Your scenario is describing what happens if there is crossing over in the middle of a gene, I think.  

There are a few answers to your question.  First of all, the chance that crossing over occurs right in the midst of a gene is small since most of our DNA is not in genes.  Second, even if crossing over occurs in a gene sequence, there are regions within a gene (called introns) that aren't expressed, and so would not necessarily affect the gene function.  Third, if crossing over occurs in a gene and not in an intron, it might still have no effect if the recombination happens at the exact same spot in the two genes.  In your example, if sequences C2 . . . Z2 is the same as C1 . . . Z1, then the exchange would not have an effect.  And, finally, assuming crossing over does occur within a gene, not in an intron, and the sequences were not aligned so you actually are missing a part of a gene, then that likely would result in a mutant allele.  However, since in a zygote you are also getting a copy from your other parent, and the chances are that copy is functional, then you would still be okay.

Answer 2

Much of our genetic material doesn't actually code for anything.  Even in the case that you do get crossing over in material that does code for something it could be something non consequential such as nose hair length and not something like a debilitating genetic disorder.

Answer 3

First of all, your question is not correct,and once again go through about  what is recombination.

  Recombination is not responsible for genetic dissorders,recombination helepful for the combination of meternal and peternal genetic meterial, only those charecters are expressed  which are dominant over other.Some times during recombination if any mismath and mutations are found they are spliced out by repair system.