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Evolution — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYEvolution4 Marks
Question
Give a brief account of evolution of vertebrates.
✓

Answer

→ About 2000 million years ago the first cellular life was found on earth.
→ About 350 million years ago, jawless fishes emerged.
→ Fish caught in South Africa in 1938, believed to be coelacanth, were thought to be extinct. → These animals evolved into known as lobefins, the first amphibians that could live on both land and water.
→ Although none of these specimens have survived to us, they were the ancestors of today's frogs and salamanders.
→ Reptiles descended from amphibians.They laid thick shelled eggs which did not dry out like amphibian eggs.
→ At the present time once again we can only see their descendants, tortoise, kashyapa and crocodile.
→ 200 million years or during which reptiles of different shapes and sizes dominated the earth.
→ Probably 200 million years ago evolved into reptiles like mastya and returned from land to water.
→ The land-dwelling reptiles were definitely dinosaurs.
→ The largest reptile Tyrannosaurus rex (T-rex) was 20 feet tall and had huge fearsome spear- like teeth.
→ About 65 million years ago, dinosaurs suddenly disappeared from the earth, which some believe to have been wiped out due to climatic changes.
→ Some even say that most of them may have evolved into birds.
→ But the truth is somewhere between these two. Because the small size reptiles of that time still exist.
→ Earlier mammals were like shrews.
Mammals were very intelligent in terms of sensitivity and overcoming fear.
→ When the reptiles decreased, the mammals took over the earth.
→ Mammals like horses, hippopotamus, bears, rabbits etc. were seen in South America.
→ Due to the continental drift, when North America joined South America, the animals of North America were scattered.
→ Due to similar continental drift, marsupials
survived in Australia because they did not have to compete with other mammals.
→ Some mammals live entirely in water. Whales, dolphins, seals and sea cows are some examples.

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Mutation explains the relationship between gene and DNA. The effects of large deletions and rearrangement in a segment of DNA results in loss or gain of gene and its function. Insertion or deletion of one or two bases changes the reading frame from the point of insertion or deletion. A classical example of point mutation is a change of single base pair in the gene for beta globin chain that results in change of amino acid residue glutamate to valine and results into a diseased condition called sickle cell anaemia.

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  1. May arise spontaneously.
  2. Is always induced by the environment.
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  4. Is not inherited.
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Mutant A-G-C-A-T-G-C-A-T-C-C-T

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Serine
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Reason: Reading frame remains unaltered with insertion or deletion of three or its multiple bases.

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