Reviewed by: Mary Anne Clark, PhD
(genetics) One of the Mendelian Laws of Inheritance, stating that the process of random segregation and assortment of pairs of alleles during gamete formation results in the production of gametes with all possible combinations of alleles in equal numbers.
The monk Gregor Mendel discovered the principles of inheritance in his work with garden peas. In his paper describing this work, he described several features of inheritance, which after the rediscovery of Mendel’s work were formalized as the Mendelian Laws. Two of these Laws are the Law of Segregation, and the Law of Independent Assortment. The Law of Independent Assortment is expressed in the inheritance of two or more different traits associated with different genes. Mendel noted that the transmission of different genes appeared to be independent events. In independent events, the probability of a particular combination of traits can be predicted by multiplying the individual probabilities of each trait. In independent events, the inheritance pattern of one trait will not affect the inheritance pattern of another.
For example, when Mendel crossed plants with round yellow peas to plants with wrinkled green peas, all of the F1 peas expressed the dominant traits round and yellow. In the F2, along with round yellow and wrinkled green peas, he observed round green and wrinkled yellow peas. Each of the dominant traits was present in ¾ of the progeny and each of the recessive traits was present in ¼ of the progeny. The four possible combinations of color and shape appeared in the ratio of 9:3:3:1, which represents the independent assortment of the genes for the two pairs of traits into the gametes. If you have ¾ yellow and ¾ round then independent events predict that ¾ x ¾ = 9/16 will be both yellow and round. The proportions of the other three combinations can be similarly calculated. Mendel observed 9 yellow round: 3 yellow wrinkled: 3 green round: 1 green wrinkled peas.
Later, after the discovery of chromosomes, and of their behavior in meiosis, it was possible to explain independent assortment as a consequence of the independent movement of each pair of homologous chromosomes during meiosis. Independent assortment of genes is important to produce new genetic combinations that increase genetic variations within a population.