Final answer:
Inversions often do not affect phenotypes as they only change gene orientation without disrupting gene sequences. Functional changes could occur if gene expression regulators are displaced, but unless crucial developmental genes are affected, there are usually no major consequences.
Step-by-step explanation:
The great majority of inversions do not cause phenotypic consequences because they involve changes that do not directly affect gene function. Inversions can occur in nature due to mechanical shear, or by the action of transposable elements, which rearrange the segments of chromosomes without necessarily disrupting gene sequences. Unless a critical gene’s sequence is interrupted, inversions generally only change the orientation of genes. This might lead to milder effects compared to aneuploid errors where there is an abnormal number of chromosomes.
However, changes in gene orientation could potentially lead to functional consequences if the regulators of gene expression are moved out of position relative to their targets. This might result in aberrant levels of gene products, but generally, unless they affect an important developmental gene, the changes are minor. Moreover, there is no selective pressure on an individual before birth as embryonic development occurs within the protective environment of the womb. Therefore, inversions without significant disruptions typically do not lead to phenotypic changes.