Mendels principle of dominance8/31/2023 At still other times, a mutation might yield a protein that can subvert the function of the "normal" protein. If the protein served in the transmission of neural impulses at the synapse, behavior could be affected, on yet another functional level (e.g., modified serotonin receptors in some cases of depression). Maybe it does not form multimers as would proteins from other alleles (sickle cell anemia). Or the protein is translated, but the variant sequence does not fold into the same shape and the protein does not fit in its receptor (insulin, in the case of diabetes) or it does not catalyze reactions (lactose intolerance). Or perhaps a mutation means that an intron is not excised or the exons are rearranged (alcaptonuria #4). For example, there may be an early stop codon that ends transcription prematurely, or a missing stop codon that generates an extended mRNA (e.g., blood type A2). Sometimes, the process is truncated and the alternative phenotype is "incomplete" or is shadowed by the other allele. What happens, then, when one gene appears to be dominant, another recessive? Just this: somewhere, the unfolding paths of expression of the dominant and recessive alleles diverge. In fact, it is not a specific process at all. Dominance is not a form of gene regulation (as portrayed in the operon model, for example). Genes are not social primates! They do not exhibit interactive behavior or political hierarchies (though the mere term "dominant" elicits such biological connotations). The term certainly evokes an image whereby one gene "dominates" another, perhaps by inhibiting transcription of the recessive allele or by actively suppressing its expression in some other way (see, e.g., Levin's popular textbook, Genes VI, page 62). Here is a simple question that a student might ask you (or has asked you, or even that you might have asked yourself): how does dominance "work"? That is, by what molecular mechanism does a gene become dominant? Answer: none. But was Mendel to blame? Ultimately, the entrenched error provides an excellent lesson on the history and nature of science. We need to purge the concept of dominance from genetics. Moreover, the term confuses students by priming or reinforcing many misconceptions about genetics. It is also misleading as a model of gene expression in diploid organisms. Briefly (and I will elaborate further on my provocative claims below), it explains nothing. ![]() ![]() Gregor Mendel is a venerable hero of biology (full-size image ). SHiPS Resource Center || Mendel's Mistake? SHiPS Resource Centerįor Sociology, History and Philosophy in Science Teaching
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