Supplement to the Law of Segregation
and
The Law of Independent Assortment
(Linkage and crossing over)
According to Mendel's Law of Segregation, the separation of alleles of one gene should not affect the separation of alleles of another gene. The separation of all alleles of any gene should be independent event and not affect by other genes.
According to the Mendel's Law of Independent Assortment, the pairing up of alleles of one gene should not affect the pairing up of alleles of another gene. The chance of combination of all situations should be the same.
In fact, there are much situations that the results are different from the predictions by the Mendel's Laws. That meant, the separation of alleles of one gene may affect the separation of alleles of another gene. That is what we called the linkage. Owning to this fact, the distribution of alleles of one gene will become possible to affect the distribution of alleles of another gene. This bleaches the Law of Independent Assortment also.
In reality, if two genes are located closed together, they would become unseparable. Then, the alleles of the second gene would be distributed as the alleles of the first gene. On the other hand, no matter how close are the two genes, there is a possibility that the two genes would be separated and showing no linkage. This is said to be the case of crossing over.
(09.11.2006)
