Mendel’s Laws of Inheritance

Gregor Mendel was an Austrian monk who conducted a series of groundbreaking experiments on pea plants in the mid-1800s. Mendels experiments on pea plants make the foundation for the field of genetics and provided important insights into how traits are passed down from generation to generation. Mendel’s experiments focused on the inheritance of certain traits, such as seed color, pod shape, and flower color, and he discovered that these traits are passed down predictably. 

Mendels Law of Inheritance

Gregor Johann Mendel (1822-1884) was an Austrian scientist, teacher, and Augustinian prelate who lived in the 1800s.  He was educated in a monastery and went on to study science and mathematics at the University of Vienna. Mendel blended his knowledge of science and mathematics and became the first one to keep count of individuals exhibiting a particular trait in each generation. This helped him to arise the laws of inheritance. 

Inheritance is the process by which genetic information is transferred from the parent to the offspring. Inheritance is the main reason that family members possess the same characteristics. Mendel’s experiments focused on the inheritance of certain traits, such as seed color, pod shape, and flower color.

Characteristics of Mendel experiments 

Mendel explains the concept of dominant and recessive alleles. The following table shows each of the traits and which traits are dominant and which are recessive.

Why was Pea Plant Selected for Mendel’s Experiments?

Mendel selected the pea plant (Pisum sativum) because of the following reasons:

• Many varieties were available with observable alternative forms for a trait or characteristics.
• Peas are normally self-pollinated; as their corolla completely encloses the reproductive organs until pollination is completed. But cross-pollination also be done.
• Peas are easily available.
• Peas have contrasting characters. The trait was seed color, pod color, pod shape, flower shape, the position of the flower, seed shape, and plant height.
• Its life cycle was short and produced a large number of offspring.
• The plant is grown easily annually plant and does not require care except at the time of pollination.

Mendel’s Experiments

Mendel worked on inheritance. Inheritance is genetic qualities that transfer from parent to offspring. Mendel took pea plants with different characteristics example-tall/short plants, white/violet flowers, etc. A gene that expresses itself in the presence of its contrasting gene in a hybrid is termed a dominant gene. A recessive gene is that whose expression is suppressed in the presence of a dominant gene e.g. in a hybrid (Tt) tall plant, the t gene for dwarfness is recessive and T gene for tallness is dominant.

• Filial generation – The generation of offspring is termed filial generation. 
• First Filial generation (F1) – The first generation of offspring produced from the parent generation.
• Second Filial generation (F2) – The second generation of offspring.

Monohybrid Cross

It is a cross in which only one character is considered at a time, e.g. in a cross between a tall and dwarf plant, the size of the stem is considered. Mendel made a cross between a pure tall (TT) and a pure dwarf (tt) pea plant. He obtained all tall (hybrid) plants in the F1 generation. On self, these plants produced tall and dwarf in the ratio 3:1 The genotypic ratio of 1:2:1 and the phenotypic ratio of 3:1 is termed the monohybrid ratio. It is a single cross between two organisms of a species that is made to study the inheritance of single pairs of genes or factors. Monohybrid cross helps to study the principle of dominance given by Mendel.

Dihybrid Cross

It is a cross between two individuals taking two contrasting traits at a time. It helps to study the inheritance of two pairs of alleles. The genotypic ratio in the F2 generation is 1:2:2:4:1:2:1:2:1 and the phenotypic ratio in the F2 generation is 9:3:3:1 This cross helps to study the principle of Independent assortment given by Mendel. For example – the cross between pea plants having yellow wrinkled seeds with those having green round seeds is a dihybrid cross.

Conclusion of Mendel Experiments

After multiple crosses Mendel concludes the following points:

• Genes are transferred from parent to new generation in pairs known as alleles.
• The genetic composition is known as genotype and the physical appearance of any organism is known as phenotype.
• Genes are independent at the time of segregation.
• Genes have 2 pairs of alleles if both of them are the same known as homozygous and of a difference then alleles are called heterozygous alleles. 

Mendel’s Law of Inheritance

Mendel had given three laws of inheritance after observing his experiments. Those are: 

Law of Dominance

The law of dominance states that the expression of only one of the forms of the parental trait in the F1 hybrid. In heterozygous condition i.e. different alleles, the dominant allele get expressed. when two different alleles are present, only one is dominant and will be expressed. F1 generation expresses dominant alleles. The suppressed allele is known as the recessive allele or trait.

         TT   ×   tt    (parents)   ——>   Tt    ; F1 generation

Law of Independent Assortment

The law of independent assortment is also the second law of Mendels. It states that completely different pairs of alleles are passed on to the offspring independently of each other that is during gametes formation, two genes segregate independently of each other as well as of the other trait. The inheritance of one gene does not affect the inheritance of any other gene. 

Law of Segregation

The law of segregation is the third law of Mendel. The law of segregation states that for any trait, each pair of alleles of a gene segregate, and one gene passes from each parent to an offspring. Two alleles do not mix when they come together in hybrid pair and are independent of each other.

Mendel’s Law Key Points

• Mendel proposed 3 laws of inheritance after doing observation from its different crosses on Pea Plant.
• Mendel’s third law i.e., the Law of Segregation states that at the time of gametogenesis, both copies of gametes segregate so that the offspring get one copy of each gene from both the parents.
• Mendel’s Law of Independent Assortment states that at the time of gametes segregation, gametes segregate independently.

FAQs on Mendel Experiment

Q1: How did Mendel control pollination in pea plants?

Answer:

To avoid self-pollination, models remove the anthers of some plants and breed them by the pollens of their desired characters.

Q2: What are the three different Laws of Mendel?

Answer:

Mendel proposed 3 laws based on his experiments:

• Law of Dominance
• Law of Segregation
• Law of Independent Assortment

Q3: Which is the universally accepted law of inheritance?

Answer:

The law of Segregation is the universally accepted law. The law of Indepent assortment has a drawback i.e. crossing over.

Q4: Why Mendels chosse Pea Plant?

Answer:

Mendel takes the Pea plant for his experiments. Pea plants have some characteristics those are:

• Pea is an annual plant with a short life cycle.
• Pea plants are easy to breed
• Pea plants show variety of traits
• Pea plant shows Self-pollination and Cross-pollination also be done.