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Mendelian Laws: A Revolution in Genetics

Updated: 1 day ago

Written by Adanur Nas

Born exactly 200 years ago, Gregor Mendel has been referred to as the father of genetics for centuries. Genetics, simply, means the study of hereditary, and hereditary means the passing on offspring traits. Offspring traits have always inflicted people’s sheer curiosity and allured people to unravel their mystery. This type of curiosity has been the one that was embedded and penetrated in human beings; therefore, different forms of science practices to uncover the mystery of genetics have taken place. Even before Mendel was born, people’s curiosity led them to assign distinctive meanings to genetics, such as accepting traits in offspring as results of a blending of the traits of each parent [1] — thus it could be stated that people relied mostly on speculation and logic rather than experiment. In that sense, Mendel’s endeavors were revolutionary since he took a different approach and experimented with pea plants. This revolution’s effects were not one-time phenomena, but rather they served as a milestone in the course of humanity.

Defined as a type of genetic disorder arising owing to alterations in one gene or results of abnormalities in the genome [2], Mendelian disorders are yet to lose their place in school books. Many students become familiar with them at the age of 11, for they are deemed as easy to understand. However, given that Gregor Mendel spared 8 years and 10,000 pea plants for the commence of genetic science [3], did his discoveries remunerate his endeavors?

Chosen for Mendel’s experiments, a pea plant acquires plenty of appealing traits. It is easy to grow and observe through self-fertilization, has hermaphrodite flowers and low generation time, and is resistant to diseases [4]. Upon his experiments and observations, he came up with 3 key principles — the Law of Dominance, Segregation, and Independent Assortment. Furthermore, before Mendel, the knowledge regarding genes were almost at zero, which signifies that the humans could not understand why one was born with green eyes or deuteranopia. Deuteranopia, in simple terms, means the inability to distinguish red and green colors. Moreover, in more school type terms, it means the inability that is inherited from X chromosome. If so, how do these discoveries assist us to understand a bigger concept, Mendelian disorders?

Conducted by the Centers for Mendelian Genomics (CMGs), their experiment estimated that there were 7,300 Mendelian disorders, which are rare and unique [5]. Those disorders can be carried on sex chromosomes or autosomes. To further elaborate, aforementioned, deuteranopia is carried on X chromosome; thus, it can manifest in both genders. However, some Mendelian diseases, such as Klinefelter’s syndrome, are carried on the Y chromosome, which indicates that those diseases could only be observed in males, unless a mutation occurs. To understand how Mendelian diseases originate, Mendel’s 3 key principles should be studied. Hereupon, a much bigger concept of diseases could be comprehended, complex diseases.

Come to heredity as the 3 key principles of Mendel, The Law of Dominance, Segregation, and Independent Assortment correspond with each other. To exemplify, excluding mutation factor, dizygotic twins of different genders whose father has deuteranopia and Klinefelter’s syndrome while mother only has a recessive deuteranopia gene can be given. The female twin will not suffer from Klinefelter’s syndrome, while the likelihood that she can face deuteranopia is 50%. On the contrary, the male twin will definitely suffer from Klinefelter’s syndrome and 50% from deuteranopia. These 2 instances could be only understood through the 3 key principles of Mendel. The Law Dominance can be understood through recessive deuteranopia, whereas the Law of Segregation can through the dizygotic twins, and the Law of Independent Assortment can through the parents’ different types of disorders.

Examined principally with Mendelian disorders, complex diseases can also be understood through the key principles — although they require more experiments since they are caused by the interaction of multiple genes and environmental factors [6]. Nevertheless, no matter how many genes or environmental factors are involved in the process, without the key principles, especially the Law of Independent Assortment, the concept of complex diseases cannot be grasped fully and efficiently. Given that complex diseases mostly violate the Law of Independent Assortment due to the genes’ proximity [7], an additional experiment is required to find out the underlying reason behind these diseases.

Summed, thenceforward the experiments of Gregor Mendel, the 3 key principles of Mendel have been used to firstly identify Mendelian disorders, and then, utilize the tenets obtained from the studies to dive into a more intricate concept, complex diseases, with supplementary studies.

  1. Miko, I. (2008). Gregor Mendel and the principles of inheritance. Nature news. Retrieved February 28, 2022, from

  2. BYJU'S. (2021, February 9). Mendelian disorders -different types of mendelian disorders. BYJUS. Retrieved March 1, 2022, from

  3. Gregor Mendel (1822-1884): CSHL DNA learning center. Cold Spring Harbor Laboratory DNA Learning Center. (n.d.). Retrieved March 1, 2022, from

  4. BYJU’S. (2021, October 14). Why did Mendel choose pea plants for his experiments? BYJU'S. Retrieved March 1, 2022, from

  5. Benowitz, S. I. (2015, August 6). Centers for Mendelian genomics uncovering the genomic basis of hundreds of rare conditions. Retrieved March 2, 2022, from

  6. Collins, F. S. (n.d.). Complex disease. Complex Disease. Retrieved March 2, 2022, from

  7. Clark, M. A., Choi, J., & Douglas, M. (2018, March 5). Laws of inheritance. Biology 2e. Retrieved March 2, 2022, from


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