Difference Between Mendelian and Non Mendelian Inheritance

Key Difference – Mendelian vs Non Mendelian Inheritance
 

Inheritance is a process in which genetic information is passed from parent to offspring. In 1860s Gregor Mendel introduced the theory of inheritance and explained how alleles are segregated, and the dominant traits are expressed in the heterozygous. This theory is known as Mendelian inheritance, and it is the simplest form of inheritance. However, scientists also observed complex inheritance patterns and they came to the conclusion that some traits cannot be inferred by Mendel’s law. Therefore, the concept of inheritance is classified into two types named Mendelian inheritance and non Mendelian inheritance. The genetic traits that follow the principals of Mendel’s law are known as Mendelian inheritance while the genetic traits that do not follow Mendel’s law are known as non Mendelian inheritance. This is the key difference between Mendelian and non Mendelian inheritance.

CONTENTS
1. Overview and Key Difference
2. What is Mendelian Inheritance
3. What is Non Mendelian Inheritance
4. Side by Side Comparison – Mendelian vs Non Mendelian Inheritance
5. Summary

What is Mendelian Inheritance?

Each cell contains a total of 23 chromosomal pairs received from the parent. Offspring inherit two homologous chromosomes, one from the each parent. Genes are the fundamental units in which characteristics are passed from one generation to next generation. A gene occurs in alleles (variants). An offspring receives one allele from one parent and the second allele from the other parent; these ultimately decide the phenotypic trait of the offspring. Of these two alleles, one is known as the dominant allele since it shows the dominant trait and the other allele is known as recessive alleles since it expresses the recessive trait when the two alleles are recessive.  Alleles can be homozygous or heterozygous for the trait.

After eight years of experiments with pea plants, Gregor Mendel introduced three key principles related to trait inheritance. They are summarized as follows.

1. The law of segregation – During the formation of sex cells (gametes), the two alleles responsible for a trait separate from each other.
2. The law of independent assortment – Alleles for different traits are distributed to sex cells independently of one another.
3. The law of dominance – When the trait is heterozygous, dominant trait will be shown in offspring due to the dominant allele.

Characteristics which follow these above-mentioned laws during inheritance are known as Mendelian inheritance. According to the third law, one dominant allele is enough to show the dominant trait in the offspring.

What is Non Mendelian Inheritance?

Non Mendelian inheritance refers to any pattern of inheritance in which traits do not segregate in accordance with the principals of Mendel’s inheritance laws. These traits show more complex inheritance patterns. Unlike Mendelian inheritance, which tells that a gene is composed only of two alleles, non Mendelian inheritance indicates that some traits are governed by multiple alleles. For example, human blood types ABO has multiple alleles.  Some traits are said to be polygenic traits which cannot follow Mendelian inheritance. These traits often show a range of phenotypes. For example, human skin colour has broad variety due to polygenic nature.

Traits which show non Mendelian inheritance produce different proportions of phenotypes in the offspring.

What is the difference between Mendelian and Non Mendelian Inheritance?

Summary – Mendelian vs Non Mendelian Inheritance

Gregor Mendel is the father of genetics. Mendel introduced fundamental laws of inheritance. He explained that the genes are in two alleles and one allele is inherited from one parent to offspring. Alleles can be dominant or recessive, and they are independently segregated during the gamete formation. Dominant trait is exhibited by the dominant allele and trait of the recessive allele is masked by the dominant allele in heterozygous. All these theories are included in Mendelian inheritance laws. Some traits follow the principals of Mendelian laws within the offspring. They are known as Mendelian inheritance. Certain traits show complex inheritance patterns which cannot be explained by the Mendel’s laws. They are known as non Mendelian inheritance. This is the difference between Mendelian and non Mendelian inheritance.

Reference:
1.Lubey, Steve. “MENDEL’S GENETIC LAWS.” Mendel’s Genetic Laws. N.p., n.d. Web. 27 Apr. 2017
2. “Non-Mendelian inheritance.” Wikipedia. Wikimedia Foundation, 23 Mar. 2017. Web. 27 Apr. 2017.

Image Courtesy:
1. “Punnett square mendel flowers” By Madprime – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Blood Types” by Zappys Technology Solutions (CC BY 2.0) via Flickr