Gregor Johann Mendel |The early life of Mendel | LAWS OF INHERITENCE BY MENDEL

 Gregor Johann Mendel 

The Early Life of Mendel

Gregor Johann Mendel was born in Austria. He was a genius and intelligent person but also very sensitive. He became mocked, and he introduced the basics of modern genetics. He was a schoolteacher in the church.

Mendel’s curiosity begins with a simple experiment on pea plants, where he notices that the pea plant is tall or dwarf, and no intermediate stage exists between them. In humans, this intermediate stage can be seen. 

He just wants to know, how characters transfer from one generation to another generation.

The questions like WHY and HOW forced him to introduce the laws of genetics.

He worked for 7 years on these pea plants (1856-1863). In 1865, he published his work in a local magazine.

 

Experiment.

• Mendel used garden peas for his experiment.
• This garden pea was tall or dwarf, no intermediate stage exists in these pea plants.
• The color of flowers, shapes of fruits, and seeds have also a great variety between them.
• Mendel made a self-fertilization between a tall pea plant and a dwarf pea plant.

 

Now, what is self-fertilization and how does Mendel do that?

The pea plant has both male and female sex organs on it. Mendel removed anthers from one plant which is the male sex part of the plant. He also covered the archegonium of the same plant and this process is called bagging. 

 

• Now, he takes pollens from other plants and fertilizes them with the archegonium of the test plant. 
• In this way, Mendel makes self-fertilization.
• Mendel thought that the new generation of pea plants must be intermediate between tall and dwarf but he was shocked by observing that all the plants were tall. This makes Mendel more curious.

He takes the newly produced tall pea plant and makes a self-cross between them.

This time he gets tall and some dwarf pea plants also. 

It was very strange for Mendel to get these kinds of results.

 

Solutions.

Mendel performs a series of experiments and uses some mathematical and statistical skills to solve this strange puzzle.

He selects seven characters of pea plants which are:

1. Height
2. Flower color
3. Flower position
4. Seed color
5. Seed shape
6. Fruit color
7. Fruit shape

 

 He performed the same experiment again but this time he considered all of these seven characters and found that some characters are constantly repeated in the F1 generation.

Now, what is the F1 generation?

F1 means first filial generation. It is the first generation that Mendel gets after he self-crossed the pea plant.

 

He noticed these characteristics in the F1 generation:

1. Plant height is tall
2. The flower color is purple
3. The flower position is axial
4. The seed color is yellow
5. The seed shape is round
6. The fruit color is green
7. The fruit shape is inflated or full

 

• He crossed the plants of the F1 generation (which all were tall) and observed the characters of the new generation. He called these plants F2 generation plants which means second filial generation.
• F2 generation plants are tall as well as some dwarfs but the maximum number of plants were tall.

Mendel concluded from his experiment that something is present that carries the characters from one generation to another generation and he called this thing a factor. 

 

This means that factors carry the characters from one generation to another generation according to Mendel.

He said that one character has two factors. 

• One factor acts as dominant, while the other factor acts as recessive. 
• The dominant factors always dominate recessive and suppress the expression of the recessive factor. 

 

Mathematical solutions:

Take any of the one characters from the above seven characters. Let’s take the character height.

Now the pea plant has two possibilities 

1. One is the pea plant is tall 
2. The second is the pea plant is a dwarf

Suppose the factors of tall pea plants are represented by capital TT and the factors of small pea plants are represented by small tt.

 

Now, the question is why do we use capital T or small t two times here?

The answer is that because the pea plant is diploid, so we use the capital T or small t twice times here.

Now, the crosse of both tall and dwarf height pea plants can be drawn as:

 

F1 progeny

 

This cross shows the capital T in every possible condition. This capital T shows the tall height of all pea plants. 

Here, we have to understand two terms: one is homozygous and the other is heterozygous.

• Homozygous generations are those who have the same sets of factors or the same genetic material. For example, capital TT is a homozygous generation.
• Heterozygous generations are those who have different sets of factors, like one capital T and one small T. The capital T factor shows the tall height while the small T factor shows the dwarf height of the pea plant.

Mendel concluded that one factor dominates the other, so the capital T dominates and the physical appearance of the pea plant is a tall height plant. The resulting F1 generations are heterozygous.

When Mendel crossed the plants of the F1 generation, he got some dwarf plants. 

We can write this cross as:

 

F2 progeny

Mendel studied one character and more than one character at a time. We used specific terms for this which are monohybrid and dihybrid.

 

Now, what are monohybrid and dihybrid?

• Monohybrid is the study of one character at a time. This character may be height, color, or shape. The ratio obtained after the monohybrid cross is called the monohybrid ratio.
• Dihybrid is the study of two characters at one time. This character may be height and color or, color and shape. The ratio obtained after the dihybrid cross is called the dihybrid ratio.

And if we are studying more than one character then it is called a poly hybrid cross and the ratio obtained after it is called a poly hybrid ratio.

 

Mendel crossed the pea plant many times and concluded the results of his experiment.

 

Conclusion:

Mendel concluded three laws from his experiment.

 

The first law is the law of segregation.

According to this law, the two factors or alleles for each trait segregate or separate, during the formation of gametes, and then the factors or alleles will combine randomly with other factors or alleles in the next generation. 

 

law of segregation

Law of dominance.

The crossing of parent's gametes produces two types of traits or factors in Mendel’s terms. One factor acts as a dominant factor or allele, and the other acts as a recessive factor. 

Only one trait or factor will be expressed in the phenotype of the next generation.

 

Law of dominance

 Law of independent assortment

 According to this law, the alleles of two different genes get sorted into gametes independently of one another. 

In other words, the factor that a gamete receives from one gene does not influence the factor received by another gene.

 

Law of Independent Assortment