Final answer:
Non-cell autonomous mutations are those that can influence neighboring cells, making them exhibit mutant phenotypes even if they do not carry the mutation. This can occur via dominant mutant alleles that affect gene product function or distribution, dysfunctional subunits reducing enzyme activity, or mutations in regulatory proteins that prompt changes in cell development or division cycle control.
Step-by-step explanation:
Non-cell autonomous mutations refer to mutations that affect not only the cell harboring the mutation but also adjacent or nearby cells, leading to a phenotypic change in those cells despite them not containing the mutant gene. This phenomenon can occur through several mechanisms. For example, in the case of Drosophila's Antennapedia mutation, a mutant allele can enhance the function or alter the distribution of a gene product such that it causes an abnormal development, like legs developing where antennae should be. Similarly, a nonfunctional mutation in a regulatory protein, such as NtcA, could lead to changes in the development of nearby cells, such as heterocyst formation in certain cyanobacteria.
Another example is when the mutant allele produces a subunit of an enzyme that becomes dysfunctional, affecting the overall function of the multimeric enzyme. If even one subunit is nonfunctional, it may reduce the activity of the whole enzyme complex substantially, with levels dropping below what is necessary for a wild-type phenotype. In this case, the dominant mutant allele effectively lowers the concentration of functional enzyme, leading to a mutant phenotype.
Finally, some mutations might alter cell cycle control proteins, potentially allowing cells to surpass checkpoints prematurely. If these cells remain viable and continue to divide, this mutation could propagate and result in further genetic instability.