CBSE Class 10 Science Chapter 9 Heredity and Evolution Revision Notes
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The process by which the features of an organism are passed on from one generation to another is called heredity.
● The process is done by genes, which define the characters of the organism.
● Gregor Johann Mendel, known as ‘Father of Genetics’, was an Austrian Monk who worked on Pea plants to understand the concept of heredity.
● His work laid the foundation of modern genetics.
● He made three basic laws of inheritance – The Law of Dominance, The Law of Segregation, and The Law of Independent Assortment.
The traits that express themselves in an organism in every possible combination and can be seen are called Dominant trait
● In Mendel’s experiment, we see that the tall trait in pea plants tends to express more than the short trait.
● Therefore, the tall trait of the plant is said to be dominant over the short trait.
A trait that is not expressed in the presence of a dominant allele is known as recessive.
● So, recessive character/trait is present in an organism but cannot be seen if a dominant allele exists.
Evolution is a tangible change in the heritable characteristics of a population over several generations. These changes can give rise to a new species or the species might change themselves to become better adapted to the surrounding environment.
Origin of species
● After a successful expedition on HMS Beagle, Charles Darwin wrote a book on what he observed at the Galapagos Islands.
● In the book named ‘The Origin of Species’, he wrote a detailed theory of evolution which was mostly based on Natural Selection.
Origin of life – Haldane’s theory
● JBS Haldane was a British Scientist who theorized that life originated from organic and lifeless matter.
● His theory was proved to be correct by Urey and Miller’s experiment.
● It was called the theory of abiogenesis.
Evolutionary evidence- fossils
● There are plenty of pieces of evidence to support the theory of evolution.
● Fossils happen to be the biggest of them.
● Fossils are the preserved remains of ancient animals or plants that died millions of years ago.
● The fossils help us understand the anatomy and even physiology of these organisms and understand how evolution worked and led to the formation of organisms that we see today.