Difference Between Mendel’s First Law and Second Law of Inheritance

After finally being able to finally understand Mendel’s experiment and his techniques (if you didn’t you can read my article on Genetic Basis of Inheritance click here and this will redirect you to my article) when it comes to laws it is a headache to understand each and so much pain to remember it so to make it easy for you I have prepared a table of difference between Mendel’s first and second law of inheritance.

Difference between Mendel’s first law and second law:

Here are 4 major differences you need to know between Mendel’ first and second law of inheritance:
Mendel’s first law Mendel’s second law
1. Mendel’s first law states that a single trait can exist in different forms or alleles 1. Mendel’s second law states that the alleles of two different genes does not depend upon each other but instead they are independently sorted into gametes
2. This law is also known as law of segregation 2. This law is also known as the law of independent assortment
3. This law is based on monohybrid cross experiment 3. This law is based on dihybrid cross experiment
4. The ratio of the offspring produced will be 3:1 4. The ratios of the offspring produced will be 9:3:3:1

What are the three laws of Mendel ?

After he conducted experiments on pea plant with the help of monohybrid and dihybrid cross, on basis of these crosses Mendel came to 3 laws which are as follows:

Mendel’s first law:

This is the first law of inheritance. This law was derived from the monohybrid cross experiment. Here where the character from two pairs of contrasting characters, which is able to express in the F1 generation is called the dominant and the one which is not able to express itself and is being suppressed is called recessive. Due to this dominance there is uniform expression in the F1 generation. 
There are factors which control the pairs. When different factor controls each character then only one character is able to express in the F1 generation which is called the dominant one and the other one which is not able to express itself is called the recessive. 
Some examples of law of dominance – In guinea pigs the the black colour coat is dominant over the white one and similarly in humans, curly hair is dominant over straight hair or brown eyes are dominant over green eyes. 
This law is not universally applicable because sometimes the dominance is not complete or is totally absent in some cases.

Mendel’s second law:

This is the second law of inheritance. Here the alleles which are in a pair stay together with mixing with each other. During gamete formation these allelic pairs separate or segregate and each gamete will receive one trait from of each pair of allele. This law is also known as law of purity of gametes. This happens in dihyrbids because in that experiment we are working with two traits so segregation takes place, but you can explain it with the help of dihybrid cross experiment.

This law is universally applicable because all sexually reproducing organisms are diploid (2n) meaning they have two sets of chromosomes and the gametes are haploid (n) meaning having only one set of chromosome. Since this most of the organisms produce sexually this law is applicable universally.

Mendel’s third law:

This is known as the third law of inheritance and also the principle of independent assortment. This law or principle is based on dihybrid cross experiment. Here, the traits of both the parents are expressed simultaneously in the progeny as we have read about it above.

Mendel also performed trihybrid cross ratio but since it is not mentioned in your syllabus we won’t be going in detail. After he performed trihybrid cross he came to a conclusion that there is indeed random fusion taking place and each gamete will receive only one allele from each pair of traits and they are independent to go anywhere and enter into any gamete they want. They do not tend to carry their parental combinations and are totally independent hence this is known as the law of independent assortment. 

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