How does a cell decide to express only the dominant allele or the recessive allele?
It doesn’t. It attempts to express both alleles. In cells with dominant mutations, two proteins will be produced. There are a number of mechanisms by which the abnormal protein can cause the phenotype even in the presence of the healthy protein. For example some connective tissue proteins form polymeric chains. The chain will consist of proteins from both alleles and as we all know, a chain is only as strong as…. Another example might be Huntington disease which does not develop until middle age. Here the healthy protein allows normal growth and development. The abnormal protein appears to do no harm initially but it cannot be properly metabolised by the body and over many years it builds up inside the brain cells until the levels are so high that the neurone dies. The mechanism of other dominant mutations such as the one that causes myotonic dystrophy is not yet known. Professor Keith Johnson of this University is researching this particular problem.
Related Questions
- Why do recessive alleles that cause lethal conditions such as the allele for cystic fibrosis, continue to exist in a gene pool?
- Why are females less likely to show a trait caused by a recessive allele linked to an X chromosome?
- How does a cell decide to express only the dominant allele or the recessive allele?
