Mendel's Laws of Inheritance

Inheritance can be defined as the process of how a child receives genetic information from the parent. The whole process of heredity is dependent upon inheritance and it is the reason that the offsprings are similar to the parents. This simply means that due to inheritance, the members of the same family possess similar characteristics.

It was only during the mid 19th century that people started to understand inheritance in a proper way. This understanding of inheritance was made possible by a scientist named Gregor Mendel who formulated certain laws to understand inheritance known as Mendel’s laws of inheritance.

Mendel’s Laws of Inheritance

Mendel’s Laws of Inheritance

Between 1856-1863, Mendel conducted the hybridization experiments on the garden peas. During that period, he chose some distinct characteristics of the peas and conducted several cross-pollination/ artificial pollination on the peas lines that showed stable trait inheritance and underwent continuous self-pollination. Such pea lines are called true-breeding pea lines.

Mendel conducted 2 main experiments to determine the laws of inheritance. These experiments were:

  1. Monohybrid Cross Experiment
  2. Dihybrid Cross Experiment

While experimenting, Mendel found that certain factors were always being transferred down to the offsprings in a stable way. Those factors are now called genes i.e. genes can be called as the units of inheritance.

The two experiments lead to the formulation of Mendel’s three laws of inheritance which are termed as:

  1. Law of Dominance
  2. Law of Segregation
  3. Law of Independent Assortment
  • Law of Dominance

This is also called as Mendel’s first law of inheritance. According to the law of dominance, hybrid offsprings will only inherit the dominant trait in the phenotype. The alleles that are suppressed are called as the recessive traits while the alleles that determine the trait are known as the dormant traits.

  • Law of Independent Assortment

Also known as Mendel’s second law of inheritance, the law of independent assortment states that a pair of trait segregates independently from another pair during gamete formation. As the individual heredity factors assort independently, different traits get equal opportunity to occur together.

  • Law of Segregation

The law of segregation states that during the production of gametes, two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. In other words, allele (alternative form of the gene) pairs segregate during the formation of gamete and re-unite randomly during fertilization. This is also known as Mendel’s third law of inheritance.

Mendel’s Experiments

Mendel experimented on a pea plant and considered 7 main contrasting traits in the plants. Then, he conducted both the experiments to determine the aforementioned inheritance laws. A brief explanation of the two experiments is given below.

  • Monohybrid Cross

In this experiment, Mendel took two pea plants of opposite traits (one short and one tall) and crossed them. He found the first generation offsprings were tall and called it F1 progeny. Then he crossed F1 progeny and obtained both tall and short plants in the ratio 3:1. To know more about this experiment, visit Monohybrid Cross – Inheritance Of One Gene.

Mendel even conducted this experiment with other contrasting traits like green peas vs yellow peas, round vs wrinkled, etc. In all the cases, he found that results were similar. From this, he formulated the laws of Segregation And Dominance.

  • Dihybrid Cross

In a dihybrid cross experiment, Mendel considered two traits, each having two alleles. He crossed wrinkled-green seed and round-yellow seeds and observed that all the first generation progeny (F1 progeny) were round-yellow. This meant that dominant traits were round shape and yellow color. He then self-pollinated the F1 progeny and obtained 4 different traits wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green in the ratio 9:3:3:1. Check Dihybrid Cross and Inheritance of Two Genes to know more about this cross.

Dihybrd Cross

After conducting for other traits, the results were found to be similar. From this experiment, Mendel formulated his second law of inheritance i.e law of Independent Assortment. Check the links given below to learn some of the important terms related to inheritance.

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Important Terms:

Practise This Question

An example of an organism in which females are the heterogametic sex and males are homogametic is: