Mendel’s Laws of Inheritance | Mendel’s Experiments

Mendel’s law of inheritance states that offspring inherited from their parents that results in similar characteristics of parents and offspring. This law of inheritance depends upon three other laws including the law of dominance, the law of segregation, law of independent assortment. Gregor Mendel was an Austrian monk who conducted groundbreaking experiments on pea plants in the mid-1800s. 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. 

In this article, we will learn about Mendel’s Laws of Inheritance, the Characteristics of Mendel experiments, and the Conclusion of the experiments.

Mendel’s 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 raise 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 inheriting certain traits, such as seed color, pod shape, and flower color.

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

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

1. 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. only one is dominant and will be expressed when two different alleles are present. 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 a hybrid pair and are independent of each other.

What are 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.

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.

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’s 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. 

Key Points of Mendel’s Laws of Inheritance

• 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.

Modern Applications of Mendel’s Laws of Inheritance

Below are the modern applications and examples of Mendel’s Laws of Inheritance: Farmers and breeders use Mendelian principles to selectively breed plants and animals with desired traits. This has led to the development of crops with improved yield, resistance to diseases, and other desirable characteristics.

• Understanding Mendelian inheritance is crucial in medical genetics. It helps in predicting the likelihood of genetic disorders and diseases in individuals based on their family history. Genetic counseling often involves explaining Mendelian patterns to individuals or families at risk.
• In genetic engineering, scientists manipulate genes to produce organisms with desired traits. Mendel’s laws guide the understanding of how genes segregate and assort, providing a basis for the design of genetically modified organisms (GMOs).
• Mendelian principles are applied in pharmacogenetics, where researchers study how genetic variations influence an individual’s response to drugs. This information is used to tailor drug treatments based on a person’s genetic makeup.
• Mendelian genetics is fundamental to the study of population genetics, which explores how gene frequencies change over time in populations. This has applications in evolutionary biology and understanding the genetic diversity within species.
• Mendelian laws play a role in forensic genetics, where DNA analysis is used to identify individuals based on their genetic profiles. Understanding inheritance patterns is essential for interpreting genetic data in forensic investigations.
• In the study of cancer genetics, Mendelian principles are used to understand the inheritance of genetic mutations that may predispose individuals to certain types of cancer. This knowledge informs cancer risk assessments and preventive measures.

FAQs on Mendel’s Laws of Inheritance

1. State the names of Mendel’s Laws of Inheritance?

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

1. How did Mendel control pollination in pea plants?

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

2. What are the three different Laws of Mendel?

Mendel proposed 3 laws based on his experiments:

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

3. Which is the universally accepted law of inheritance?

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

4. Why Mendels chosse Pea Plant?

Mendel opted for pea plants in his experiments due to their beneficial traits, including a short life cycle, easy breeding, diverse traits for studying inheritance, and the ability to undergo both self-pollination and cross-pollination conduct controlled mating.

5. What is Mendel’s law of dominance?

Mendel’s law of dominance asserts that when an organism carries two different alleles for a particular trait (heterozygote), one allele will overshadow the expression of the other. Instead of a combined influence on the phenotype, only the dominant allele will manifest its characteristics.