Difference Between Mendel’s First and Second Law

The key difference between Mendel’s First and Second Law is that Mendel’s first law describes the segregation of the alleles of a given locus into separate gametes during gametogenesis while Mendel’s second law describes the independent transmission of alleles of genes into daughter cells without the influence of each other.

Mendelian inheritance describes Mendel’s first and second laws in genetics. These laws mainly explain how a trait passes from parents to offspring through sexual reproduction in eukaryotic organisms. Gregor Mendel analyzed this phenomenon for the very first time in the 1850s. During his experiments, he made control crosses between true-breeding garden pea varieties, which had easily identifiable and inheritable differences including plant height, seed colour, flower colour, and seed shape. He published the success of his work in 1865 and 1866. His findings were later on developed as Mendel’s laws. The main aim of this article is to discuss the difference between Mendel’s first and second law.

CONTENTS

1. Overview and Key Difference
2. What is Mendel’s First Law
3. What is Mendel’s Second Law
4. Similarities Between Mendel’s First and Second Law
5. Side by Side Comparison – Mendel’s First vs Second Law in Tabular Form
6. Summary

What is Mendel’s First Law?

Mendel’s first law or the law of segregation describes the segregation of alleles and discrete inheritance of characteristics. The law further explains that during the production of gametes of an individual, chromosomes first separate and each gamete gets only one set of individual chromosome pair. Further, this allele segregation process occurs via meiotic cell division.

Hence, Mendel’s first law talks about a single trait and the 50:50 chance of getting the allele to each gamete during gametogenesis.

What is Mendel’s Second Law?

Mendel’s second law or the law of independent assortment states that during meiosis alleles of one trait assort independently from the alleles of another trait, and they are distributed to daughter nuclei with equal probability.

The law considers the behaviour of independently assorting non-homologous chromosomes. It mainly explains the independent assortment of two or more traits. According to the second law, without the interference of the other trait, all the traits are independently transmitted to the daughter cells.

What are the Similarities Between Mendel’s First and Second Law?

• Mendel’s first and second law are the basics of inheritance of traits from parent to offspring.
• Moreover, both laws explain the transmission of alleles.

What is the Difference Between Mendel’s First and Second Law?

Mendel’s first law describes the segregation of the alleles of a given locus into separate gametes during gametogenesis while Mendel’s second law describes the independent transmission of alleles of genes into daughter cells without the influence of each other. Thus, this is the key difference between Mendel’s first law and second law. Mendel’s first law is also called the law of segregation while the second law is also called the law of independent assortment.

Furthermore, the first law is mainly applicable to a single trait while the second law is applicable to two or more traits. Thus, this is another difference between Mendel’s first and second law. The below infographic provides more details on the difference between Mendel’s first and second law.

Summary – Mendel’s First vs Second Law

Mendel’s first law describes the separation of the two alleles of each gene during the production of gametes and the equal chance of each gamete to get one allele. On the other hand, Mendel’s second law describes the independent transmission of alleles of one gene from the alleles of another gene into daughter cells. Second law shows that there is no interaction or influence between genes when the alleles of each gene transmit to daughter cells. However, these first and second laws are the building blocks of trait inheritance from parents to offspring. Thus, this summarizes the difference between Mendel’s first and second law.

Reference:

1. “The Law of Segregation.” Khan Academy, Khan Academy, Available here.
2. “Mendelian Inheritance.” Wikipedia, Wikimedia Foundation, 12 Mar. 2019, Available here.

Image Courtesy:

1. “Mendel 2 miguelferig” By Miguelferig – Own work (CC0) via Commons Wikimedia
2. “Independent assortment & segregation” By LadyofHats – Own work (Public Domain) via Commons Wikimedia