Mendel’s Law of Segregation

Our Objective

To verify the Mendel’s Law of Segregation 

 

The Theory

Let’s begin with inheritance  

The passing characters from one generation to the next from the parental trait is known as ‘Heredity’ and the process is known as “inheritance.” Mendel studied the inheritance in green pea plants and proposed three laws in 1865.  

Based on the research work he formulated,  

  • The law of Dominance  
  • The law of Segregation  
  • The law of independent assortment. 

He studied the inheritance pattern of one gene by crossing the tall (T) and dwarf (t) green pea plants and obtained the seeds and grew them as a model of hybrid generation. He termed that as F1 progeny (or) F1 generation. He observed that all the F1 progeny having only one type of parental trait. Then he self - pollinated the F1  plants and obtained some of the offspring are dwarf plants that was not seen in F1 generation. The proportion of these results obtained as ¼th of the F2 plants were Dwarf and the rest of ¾th were Tall. The F2 generation were showed the proportional ratio of 3:1.  

He conducted the experiments using seven green pea plants and got several types of results as his observations. 

   

Sl.no 

Character 

                      Contrasting trait 

Seed Colour 

Yellow 

Green 

Seed Shape 

Round 

Wrinkled 

Stem Height 

Tall 

Dwarf 

Flower Colour 

Violet 

White 

Flower Position 

Axial 

Terminal 

Pod Shape 

Inflated 

Constricted 

Pod Colour 

Green 

Yellow 

 

Based on the experiments he addressed that there is something passing through the information from one to another during the fertilisation (in the stage of meiosis) and he named as “factors” now called “Genes” (Containing a set of contrasting traits called as alleles) and it represents as the Unit of inheritance.   

Using the height of the plants from one gene namely T – tall and short t – Dwarf the F1 progeny shows the homozygous genotype of either TT (or) tt and after the self-pollination F2 progeny shows heterozygous phenotype of Tt. 

Law Of Segregation  

Based on the research work he addressed the law that states, when the pair of dissimilar factors were crossed and delivered the results of one dominate the others. The dominating factor known as “dominant” and the other one is “recessive.” This law supports the fact that alleles do not blend and both traits are restored in the F2 generation even though one of them is not present in the F1 stage.

Let us Discuss with Punnett Square  

The Punnett square is the graphical representation which helps to calculate the probability of the traits occurring in the genetic cross. It was developed by British geneticist Reginald C. Punnett. The trait arrangements were written as the top row and the left column of the square. According to the Mendel’s law, from the parental traits Tall (TT) and Dwarf (tt) were results heterozygous F1 progeny (Tt). The F1 Progeny (Tt) was self-pollinated in equal proportion to produce the F2 generation.  

During the fertilisation process both traits of T having a 50 percent chance in the genotype as well as both traits of t having a 50 percent chance in the genotype. As a result of random fertilisation, the genotype of the F2 progeny was TT, Tt and tt. 

From the Punnett square it is clearly explained that ¼th of TT and ½ of Tt and ¼th of tt of the genotypic character were expressed during the fertilisation process. Most of the traits having the T (TALL) during the segregation so the phenotype of the character was expressed as ¾th of tall and ¼th of dwarf. From the results, it shows the phenotypic ratio of 3:1 and genotypic of 1:2:1.  

 

Learning Outcomes  

  • Students learn about the study of inheritance.   
  • Students learn about the Mendel’s law of segregation. 
  • Students learn about the Punnett square and probability connections.