Question

Why is Mendel’s Second Law not always valid for two or more phenotypical traits of an individual?

Answer 1

Mendel's second law postulates that two or more different traits are also conditioned by two or more pair of different factors and that each inherited pair separates independently from the others. In other words, gametes are formed always with an aleatory representative of each pair of the factors that determine phenotypical characteristics.

Mendel’s second law is also known as the law of independent segregation of factors, or law of independent assortment.

Mendel’s second law is only valid for genes located in different chromosomes. For genes situated in the same chromosome, i.e., linked genes (genes in linkage) the law is not valid since the segregation of these genes is not independent. Therefore, Mendel’s Second Law is not valid for phenotypical features conditioned by genes located in the same chromosome (genes under linkage), since these genes, known as linked genes, do not separate during meiosis (except for the phenomenon of crossing over).