Question

Answer the following questions.
a. How are the hereditary changes responsible for evolution?
b. Explain the process of formation of complex proteins.
c. Explain the theory of evolution and mention the proof supporting it.
d. Explain with suitable examples importance of anatomical evidences in evolution.
e. Define fossil. Explain importance of fossils as proof of evolution.
f. Write evolutionary history of modern man.

Answer 1

a. Heredity is the passing of traits from parents to offsprings. These traits which are passed from one generation to another are called inherited traits as they are inherited from the previous generation. Evolution refers to the changes which occur in these inheritable traits over a long period of time. These changes allow organisms to survive with changing environment and provide an advantage over other species who cannot survive in that environment. Changes in these inheritable characters, provide better chances of survival and reproduction and thus result in the evolution of species.

b. The synthesis of proteins occurs according to the central dogma. The central dogma explains how genetic information flows from DNA to RNA to make a functional protein.
It suggests that DNA contains all the information required to synthesise a protein and the RNA acts as a messenger which carries this information to ribosomes (a type of cell organelle). The central dogma is represented as:

$\mathrm{DNA}\stackrel{\mathrm{Transcription}}{\to }\mathrm{mRNA}\stackrel{\mathrm{Translation}}{\to }\mathrm{Protein}$

Transcription: Transcription results in the formation of an mRNA using DNA as a template. This process takes place in the nucleus. You must be aware that DNA is made up of two strands. But in this process only one strand of DNA is required and this one strand is used as the template for the synthesis of the mRNA.

An enzyme, RNA polymerase, helps in this process. It helps in copying the information from DNA strand to mRNA. Once this process is complete, the RNA polymerase dissociates from the strand and the newly synthesised mRNA is released from the nucleus.
Like DNA, RNA is also made up of nucleotides but there is a difference. RNA contains the nucleotide Uracil (U) instead of thymine which is present in DNA. This uracil pairs with adenine just like thymine.

Once the process of transcription is complete, the newly synthesised mRNA is released from the nucleus into the cytoplasm.

Translation: The newly synthesised mRNA contains information in the form of codons. A codon is a sequence of 3 DNA or RNA nucleotides that correspond with a specific amino acid. Since, these codons contain 3 nucleotides, they are called triplet codon.

Process of translation:

• After the mRNA is released into the cytoplasm, it reaches the ribosomes where the process of translation occurs. Each mRNA can be made up of thousands of triplet codons.
• Two other types of RNAs, i.e. tRNA and rRNA, also participate in this process.
• Each tRNA has an anticodon which has the sequence complementory to the codon on mRNA. These tRNAs supply the amino acids as per the codons on the mRNA.
• The amino acids which are brought by the tRNA are joined together by peptide bonds. This process is carried out with the help of rRNA.
• During this process, the ribosome moves from one end of the mRNA to the other by a process known as translocation.

At the end of this process a protein is formed which undergoes further modifications to form a fully functional protein.

c. There are various theories of evolution but the most acceptable one is the theory of 'Gradual development of living organisms'. According to this theory, the first living material which is the protoplasm was formed in ocean. Gradual changes resulted in the formation of unicellular organisms and further developments resulted in the formation of larger and complex organisms. However, these changes did not occur overnight, they were slow and gradual changes which took almost 300 crore years. These changes and development are often referred to as evolution and are the prime cause of diversity of plants and organisms which we see on earth today. There are various evidences which support evolution:

Morphological evidence- Similarity in morphological features of animals and plants is an evidence that they have evolved from common ancestors. For example: In animals similarities like
structure of mouth, position of eyes, structure of nostrils and in plants, similarities in characters like leaf shape, leaf venation, leaf petiole represent common ancestry.

Connecting links- Connecting links refers to plant and organisms which show characteristics related to two different groups. For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle, and parapodia-like organs which are similar to annelids. It also show tracheal respiration and open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals because it lays eggs like reptiles and has mammary glands like mammals.

Embryological evidence- Embryology is used as one of the evidences of evolution. Comparative study of embryos shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually. This similarity in the development of embryos represents common origin of organisms.

d. Anatomical evidences help us to study how species have evolved over a period of time. Analogous structures support the theory of evolution and explain the fact that how species build up adaptations in order to fit in an environment whereas homologous structures help us to understand common ancestry. For example, if we compare the hands of humans with cat’s foreleg, flipper of whale and patagium of bat, we see that each of these organism use these structures are differently. But still there is a similarity between the structure of bones and joints which indicates that somewhere or the other these animals may have originated from common ancestors. This is an example of homology. Another example which explains analogous features is the arctic fox and the ptarmigan bird, Both of them change colours from dark brown to white during seasonal changes. They do not show common ancestry in way but since, they are found in the same habitat they are adapted to colour change.

e. The evolutionary history of modern man is as follows:

Year	Evolution
15 million years ago	Dryopithecus (ape-like) and Ramapithecus (man-like)
3 − 4 million years ago	Man-like primates
2 million years ago	Australopithecines, also called Homo habilis,lived in East Africa
1.5 million years ago	Homo erectus
1,000 − 40, 000 years ago	Neanderthal man
75, 000 − 10, 000 years ago	Homo sapiens