Recessive gene interactions

It was shown81 that for a wide variety of gene interactions the mutation component is 1 for a detrimental trait determined solely by balance between mutation and selection. If the trait has a quantitative basis, the principle still holds true. For example, if the disease is expressed only when a particular threshold of the underlying variable is exceeded, the mutation component is still 1. The dominance of the gene also does not matter even a rare recessive disease has a mutation component of 1. 

Huynh, D. P., et al.. The autosomal recessive juvenile Parkinson disease gene product, parkin, interacts with and ubiquitinates synaptotagmin XL Hum Mol Genet, 2003, 12(20), 2587-97. 

A major reason for using merodiploids is to study the interaction between different alleles of the same gene. This often tells us a great deal about how a gene or the gene product functions. The two simplest types of interactions are dominant and recessive. A cell that is z+/Fz behaves like a z+ cell as far as the metabolism of j8-galactosidase is concerned. Therefore, the z+ allele is dominant to the z allele, or conversely, the z allele is recessive to the z+ allele. 

Alleles are classified by how they interact with each other. The red-hair allele is recessive —i.e., one such gene on each member of the chromosome pair is required for the trait to be manifest. The nonred-hair allele, in contrast, is dominant —i.e., a person with either one or two of these genes has nonred hair. It is customary to designate dominant alleles with capital letters and recessive alleles with lower-case letters. If r stands for the red-hair gene and R for its alternative, rr persons will have red hair, and Rr and RR will not. 

The benefit of allowing mutants that are less fit than the parent is dependent on the ruggedness of the fitness landscape. If the landscape is very rugged, then an initially bad mutation may be required to ultimately benefit from a coupling interaction. In nature, many mechanisms allow unfit genes to survive. For example, some genes are recessive or are... 

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