Inheritance and Heredity
Concept: Mendel’s Experiments
What are genes?
Traits are the characters we have in our bodies. We inherit these traits from our parents. But what leads to this transmission of traits?
- The transmission of traits occurs due to the transfer of genes. Genes carry information that determines our characters or traits.
- Genes are present in chromosomes, situated in the nucleus of all cells in our body.
- The nucleus acts as the ‘brain of the cell’ and guides the cell to perform all the activities.
- One human cell comprises 23 pairs of chromosomes, i.e. 46 chromosomes.
- There are around 25,000-35,000 genes located in each cell.
Expression of traits:
- Genes have a particular function to perform.
- Genes are made up of DNA or deoxyribonucleic acid.
- Every gene is responsible for the synthesis of one particular type of protein.
- Now, protein plays a vital role in almost every function of our bodies.
- The synthesis of proteins from the genes is responsible for the development of traits in our bodies.
- The type of genes we have thus decide the type of our hair, skin, height, facial features etc.
- We get genes from both our parents, half from our mother and half from our father.
What will happen if only half of the genes are not inherited from the parents?
- If genes are not halved at the time of inheritance, then the newborn individual's genetic makeup would not be the same as the other members of the species.
- It would get doubled in the new individuals.
How are traits expressed?
- The expression of traits depends on the types of genes inherited from the parents. Examples:
- Rita’s father and mother have black and red hair, respectively.
- Rita may either have red or black hair, depending on the genes she inherits from her parents.
- The occurrence of red and black hair will depend on which gene is dominant and which gene is recessive.
Dominant and recessive genes:
- We know that genes are present in pairs.
- The dominant gene expresses itself even if it is not present in pair.
- The recessive gene expresses itself only if it is present in pair.
- Considering the example discussed above, we can conclude the following points—
- If the gene for black hair is dominant, then Rita will have black hair irrespective of the gene she inherits from her mother.
- Similarly, if the gene for red hair is dominant, then Rita will have red hair irrespective of the gene she inherits from her father.
Let us see the dominant and recessive genes in the following family.
- Both father and mother are tall, i.e. they have the dominant gene.
- The child who inherits the dominant gene from a parent is tall.
- However, the child who does not inherit the dominant gene is short.
Gregor Mendel—The Father of Genetics:
- The branch of science that deals with studying genes and their inheritance is called genetics.
- Gregor Mendel is considered the Father of Genetics for his work on genes.
- He was born in 1822 in a poor family in Austria.
- Through his work on pea plants, he discovered the laws of inheritance.
- In his work, he stated that genes occur in pairs. People did not understand his conclusions at that time. His work was restudied after his death.
Why did Mendel choose the pea plant for his experiment?
- The pea plant showed various contrasting factors, either dominant or recessive.
- There was no scenario where a trait intermediate between dominant and recessive was expressed.
- A pea plant is easy to grow and maintain.
- It made the experiments be conducted efficiently without any complex results.
- Mendel grew around 10,000 pea plants and kept track of the progenies.
- He recognised mathematical patterns of inheritance from generation to generation, which you will study in detail in higher classes.
He concluded the following things after his experiments—
- Law of segregation: It stated that each inherited trait is controlled by a pair of genes. These genes are randomly segregated in the cells of parents during the formation of gametes.
- Law of Independent Assortment: The genes of different traits are not affected by each other. They are inherited independently by the next generations.
- Law of Dominance: A recessive gene would not affect the expression of a trait in the presence of the dominant gene. A dominant gene would express itself even if the recessive gene is present.
Now let us understand the laws on inheritance with examples:
- In the previously stated example, both the genes for tall and short were inherited by the siblings. It validates the law of segregation and independent assortment.
- The tall child may have inherited the gene for short height, but he is tall because he inherited one dominant gene for tallness. It validates the law of dominance.
Contrasting traits of the pea plant:
|Position of flower||
Axial flower: It is the flower located in the middle of the plant stem.
Terminal flower: It is the flower located at one end of the plant stem.
Gametes: Sex cells involved in sexual reproduction.
Did You Know?
- Gregor Mendel worked as a gardener and studied beekeeping when he was a child.
- He belonged to a poor family and decided to become a monk to escape poverty and continue his education.
- The scientific name of the pea plant is Pisum sativum, on which Mendel conducted his experiments in a monastery.
- The most important contribution of Mendel in the field of genetics is discovering the concept of a dominant and recessive gene.