|
The frequency of the allele for the disease would increase since the natural selcetion pressure against its perpetuation into the next generation would be relaxed by allowing more affected individuals into the reproductive gene pool.
"Can u please explain the difference between results that show selection to those favoring heterozygotes?"
I don't understand this. What are we comparing to what to find differences. Results (I assume you mean results of mutation or other alterations of the gene pool) may favor selection, but I don't know how results show selection. Any change that helps the organism to reproduce at a higher frequency, like having a longer total reproductive age, or something that allows the organism to compete better with other members of the population and father or mother more offspring will be selected for.
In addition, there are situations which favor heterozygotism, such as sickle cell trait in malarial regions of the world. Homozygotes both with the sickle allele and without die faster than heterozygotes, since they either have sickle cell anemia and die from that, or are more prone to malaria and die from that. Therefore, in regions of the world where malaria caused by Plasmodium falciparum is common, the allele for sickle-cell hemoglobin is also common. Children who inherit one gene for the "normal" beta chain of hemoglobin and one sickle gene are more likely to survive than children homozygous for the sickle allele, who, as stated, die young from sickle-cell disease, or children homozygous for the "normal" beta chain, who are far more susceptible to illness and death from falciparum malaria than are heterozygotes.
Hence the relatively high frequency of the allele in malarial regions. When natural selection favors heterozygotes over both homozygotes, the result is called balanced polymorphism. It accounts for the persistence (selection for) of an allele even though it is deleterious when homozygous.
Does that answer your question?
 | 
03-09-2008, 06:04 PM
Similar Threads 
Linear Mode
