Maharashtra Board Class 10 Science Part 2 Chapter 1 Heredity and Evolution PDF Download

1. Heredity And Evolution

Can you recall?

1. Which component of the cellular nucleus of living organisms carries hereditary characters?

2. What do we call to the process of transfer of physical and mental characters from parents to the progeny?

3. Which are the components the DNA molecule?

Heredity And Hereditary Changes

You know that heredity is the transfer of biological characters from one generation to another via genes. Johann Gregor Mendel is pioneer of the modern genetics. Around the period of 1886, it took a long time for him to understand the conclusions of his research about heredity. In 1901, the reasons behind the sudden changes were understood due to the mutational theory of Hugo de Vries. Meanwhile in 1902, Walter and Sutton observed the paired chromosomes in the cells of grasshopper; until then it was not known to anyone. Research started in the direction of finding the nature of genetic material when it was proved that genes are carried via chromosomes. Through which 1944, trio of scientists Ostwald Avery, Mclyn McCarthy and Colin MacLeod proved that except viruses, all living organisms have DNA as genetic material.

In 1961, the French geneticists Francois Jacob and Jack Monad proposed a model for process of protein synthesis with the help of DNA in bacterial cells. It helped to uncover the genetic codes hidden in DNA. Thereby, the technique of recombinant DNA technology emerged which has vast scope in the field of genetic engineering.

The science of heredity is useful for diagnosis, treatment and prevention of hereditary disorders, production of hybrid varieties of animals and plants and in industrial processes in which microbes are used.

Teacher's Note

Heredity is how children get features from their parents. Just like you have your mother's eyes or your father's height, genes pass down family traits.

Exam Trick

Remember: Genes = instruction book for body. DNA = book, genes = pages in the book.

Points to Remember

Heredity means passing traits from parents to children.
Johann Mendel discovered the rules of heredity.
Genes carry information on DNA molecules.
Mutations are sudden changes in genes.
All living things use DNA to store information.

Transcription, Translation And Translocation

Can you tell?

1. Sketch and explain the structure of DNA and various types of RNA.

2. Explain the meaning of genetic disorders and give names of some disorders.

With the help of RNA, the genes present in the form of DNA participate in the functioning of cell and thereby control the structure and functioning of the body. Information about protein synthesis is stored in the DNA and synthesis of appropriate proteins as per requirement is necessary for body. These proteins are synthesized by DNA through the RNA. This is called as 'Central Dogma'. mRNA is produced as per the sequence of nucleotides on DNA. Only one of the two strands of DNA is used in this process. The sequence of nucleotides in mRNA being produced is always complementary to the DNA strand used for synthesis. Besides, there is uracil in RNA instead of thymine of DNA. This process of RNA synthesis is called as 'transcription'.

Teacher's Note

Transcription is like copying information from a book into your notebook. mRNA copies the DNA message so it can travel from nucleus to make proteins.

Exam Trick

Remember: Transcription = DNA to RNA (copying). Translation = RNA to protein (building).

Points to Remember

Transcription is making mRNA from DNA.
mRNA carries messages from DNA.
RNA has uracil, DNA has thymine.
Only one DNA strand is used for transcription.
mRNA is complementary to DNA strand.

The mRNA formed in nucleus comes in cytoplasm. It brings in the coded message from DNA. The message contains the codes for amino acids. The code for each amino acid consists of three nucleotides. It is called as 'triplet codon'.

Dr Har Govind Khorana, a scientist of Indian origin has made an important contribution in discovery of triplet codons for 20 amino acids. For this work, he has been awarded with the Nobel Prize in 1968, along with two other scientists.

Each mRNA is made up of thousands of triplet codons. As per the message on mRNA, amino acids are supplied by the tRNA. For this purpose, tRNA has 'anticodon' having complementary sequence to the codon on mRNA. This is called as 'translation'. The amino acids brought in by tRNA are bonded together by peptide bonds with the help of rRNA. During this process, the ribosome keeps on moving from one end of mRNA to other end by the distance of one triplet codon. This is called as 'translocation'. Such many chains come together to form complex proteins. These proteins control various functions in the body of living organisms and their appearance too.

Living organisms can produce new individuals like themselves due to genes only and some of those genes are transmitted to the next generation without any changes. Due to this, some of the characters of parents are transmitted to their offsprings. However, sometimes sudden changes occur in those genes. Sometimes, any nucleotide of the gene changes its position that causes a minor change which is nothing but the 'mutation'.

Some mutations may be minor but some may be considerable. Ex. Mutation may cause the genetic disorders like sickle cell anemia. This is a everlasting process and it is one of the proof for Darwin's theory of natural selection.

Teacher's Note

Translation is like reading the copied message and building a protein from it. tRNA brings amino acids and puts them together like building blocks.

Exam Trick

Remember: Codon = 3 letters code on mRNA. Anticodon = opposite code on tRNA. They match like a lock and key.

Points to Remember

Translation means making proteins from mRNA message.
Codons are groups of 3 nucleotides.
tRNA has anticodon that matches codon.
Translocation is ribosome moving along mRNA.
Mutations are sudden changes in genes.

Evolution

Can you recall?

1. What is the function of the appendix of our digestive system?

2. Are our wisdom teeth really useful for chewing the food?

3. Why did the huge animals like dinosaur become extinct?

4. Why are many species of animals and birds getting extinct?

3.5 billion years ago, life had been non existent on the Earth. At the beginning, there may have been only simple elements in the ocean on the Earth and simple type of organic and inorganic compounds may have been formed from those. Complex compounds like proteins and nucleic acids may have formed over the long period from those simple compounds. First primitive type of cells may have been formed from the mixture of different types of organic and inorganic compounds. Number of those cells may have increased at the cost of surrounding chemicals. There may had been some differences among those cells and according to the principle of natural selection, some may have shown good growth and some may have perished which could not adjust with the surrounding.

At present, crores of species of plants and animals with huge diversity regarding shape and complexity are present on the Earth. Animal diversity ranges from the unicellular Amoeba and Paramoecium to man and giant whale. The plant diversity consists of various species ranging from unicellular Chlorella to the huge banyan tree. The life exists on Earth everywhere from equator to both the poles. Organisms are present at all the places like air, water, land, rock, etc. Humans have shown curiosity about origin of life and reasons for such a great diversity in life present on the Earth since ancient period. Different theories about origin and evolution of life have been proposed till today of which theory of 'Gradual development of living organisms is accepted.

A Peek Into History

Many philosophers and religious scholars have written their views about formation of life. There seems to be a thorough discussion over the formation of Universe, in various cultures like Indian, Chinese, Roman, Greek, etc. Various cultures have noted different type of information about planets, stars, the 'panchmahabhuta', living organisms, etc. in the form of poetry, stories and religious / sacred books.

Evolution is the gradual change occurring in living organisms over a long duration. This is a very slow-going process through which development of organisms is achieved. All the stages in changes occurred in various components ranging from stars and planets in space to the biosphere present on the Earth should be included in the study of evolution. Formation of new species due to changes in specific characters of several generations of living organisms as a response to natural selection, is called as evolution.

Internet is my friend

Collect the information from internet about Big-Bang theory related with the formation of stars and planets and present it in your class.

Theory Of Evolution:

According to this theory, first living material (protoplasm) has been formed in ocean. In due course of time, unicellular organism was formed. Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed. All those changes were slow and gradual. Duration of all these changes is at must 300 crore years. Changes and development in living organisms had been all round and multi-dimensional and this led to evolution of different types of organisms. Hence, this overall process is called as evolution which is organizational. Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.

Teacher's Note

Evolution means slow changes in living things over many years. Just like how your ancestors looked different from you, animals also changed over millions of years.

Exam Trick

Remember: Evolution = very slow change over very long time. Not sudden change. Takes crore of years, not days.

Points to Remember

Evolution is gradual change in organisms over long time.
Life began in ocean as simple cells.
Complex organisms developed from simple ones.
Evolution took about 300 crore years.
Natural selection helps evolution happen.

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