[Biology Class Notes] on Heredity and Evolution Pdf for EXAM

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Heredity is the study of the transmission of genetic characters and variation from one generation to the other generation. Heredity involves the chromosomes transfer from parents to the progeny or from one person to another person. Therefore,  chromosomes are the base of heredity. The physical basis of heredity is genes while the chemical basis of heredity is DNA. The process of transfer of heredity character from generation to generation is called Genetics. The name genetics was first coined by Watson in 1905. Gregor John Mendel was the first scientist who gave the idea of heredity based on his experiments in 1822- 1884 and is also known as ‘Father of Genetics’.

Important Facts Related to Heredity

• The first scientist who studied the inheritance of traits was George Mendel who chose pure breeding varieties and pure lines of pea plant for his experiment.

• The genotype is the genetic constitution of an organism while the external feature of organisms like color and behavior denotes the phenotype.

• According to the experiment performed by Mendel slope and inheritance can be categorized as follows:

• Law of Dominance: Offspring of crossbreed parents only show dominant characteristics in the F1 generation.

• Law of Segregation: In F2 generation both the character which is governed by the gene is separated.

• Law of Independent Assortment: During dihybrid and trihybrid cross two or three pairs of characters are taken. These characters segregate separately without depending on others in the F2 generation.

Traits are Transferred by Heredity and Variations 

Both animals and plants have common variations that reproduce by sexual means because sexual reproduction is biparental and involves the process of fertilization and meiosis and traits are received by the progeny from both the parents.

Introduction to What is the Evolution

More and more creation of organisms by gradual changes from low categories animals to higher animals is called evolution.

Darwin’s Theory of Evolution

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Charles Robert Darwin in 1809 -1882, explains the evolutionary principle in his book ‘The origin of species’. The theory proposed by him is popularly known as “Theory of natural selection” or Darwinism. 

Darwin explained that despite having the enormous potential of fertility, the population of organisms remains within a limit. It is due to the struggle between the members of the same species and different species for food, space, and mate. Struggle eliminates the unfit individuals. The fit organism possesses from a variation which is favorable and they can leave the progeny to continue the favorable variations.

The variation which when accumulated for a long time gives rise to the origin of new species with progress in genetics, the source of variation was explained and Darwin’s theory was modified. Now, the most accepted theory of evolution is  ‘Modern synthetic theory’, in which the origin of species is made on the interaction of genetic variation and natural selection.

His Main Ideas Include:

• Environmental: It is the struggle between the animals and the environment. A change in climate affects adversely resulting in the extension of some and the survival of others.

• Universal Occurrence of Variations: The “departures from the original pattern” and changes in animals are termed as a variation. Darwin believed that continuous and useful variation constitutes the raw material of evolution.

• Survival of the Fittest or Natural Selection: In the struggle for existence, only those organisms survive which possess the most useful variations. This phenomenon of Darwin was called ‘Natural selection’ and Spencer gave it a new name which is known as ‘Survival of the fittest’.

• Inheritance: Variations that are useful are inherited by the offspring.

• Origin of New Species: To form a new species, favorable variations accumulate over generations.

Facts Related to Darwin’s Theory

• To explain the inheritance of characters from one generation to another, Darwin proposed ‘Theory of Pangenesis’. 

• According to this theory, each somatic cell produces a page. All the pages from body cells that accumulate in gametes and transfer characters to the next generation.

• Most of the biologists agree with Darwin’s theory as the best explanation for organic evolution but still, there are a number of objections for this theory.

Importance of Evolution

Evolution helps in a better understanding of the various aspects of life which includes how a species came into existence, and how it became extinct and several. It also helps to know about the various other factors like their behavior and habitats.