Question

Explains in details how broad expressivity and incomplete penetrance can complicate the genetic analysis of phenotypic traits.

Answer 1

The genetic analysis is used to identify the relation of a particular genotype with its expression or phenotypes. It also gives the about genetic nature and their behavior which broadly affect the phenotype. We cannot see the genetical factors which determine the fate of specific characters. So we statistically observed the phenotypes, their distribution, and inheritance pattern to create the fundamental ideas about the genetic characters which govern the particular phenotype.  Statistical data grant an enormous opportunity to design the genetic architecture by analyzing the phenotypic distribution. Naturally, the phenotypic distribution follows some rules otherwise it was not possible to analyze them in an organized way. If the phenotype of the relative genotype becomes random then the statistical data will lose their significance and the determination of the genetic factors will be much more complex. The problem with incomplete dominance and broad expressivity is exactly like that. Both of the events create randomness and statistical data failed to justify them. It is natural that if a gene express then a particular phenotype will develop in a particular ratio which will allow discovering their genetic behavior. But with incomplete penetrance and broad expressivity, the ratio of the phenotypic characters will not follow the rules and so it will mislead to a different conclusion about their genetics. By this way, broad expressivity and incomplete penetrance can complicate the genetic analysis of phenotypic traits.