Class 12th Exam Biology VVI Objective Subjective Question Evolution Chapter

7. Evolution

1. What is geological time scale? It is classified into eras. Name the eras.

Ans.– Earth originated around 4.6 billion years ago from a burning gaseous mass. Geological time scale is the correlation between time periods of the past and fossili- ferous rocks. First geological time scale was proposed by Italian scientist Giovanni. First life appeared about 3500 million years ago. Geological time scale has two major divisions and six di divisions. Divisions of geological time scale are called eras. Periods are usually distinguished on the basis of system of rocks and their associated fossils, eg.- Carboniferrous, Cretaceous. Eras are

(i) Coenozoic era   (ii) Mesozoic era    (iii) Palaeozoic era    (iv) Proterozoic era  (v) Archaeozoic era

2. What do we understand by the following? 

(a) Micro mutation   (b) Macro mutation   (c) Chromosomal mutation

Ans.- (A) Micromutation : Primary factors of biological evolution such as germinal drifts, mutational changes and natural selection show some micro changes in its gene pool, and it cause micro evolution. Micro evolution changes the balance between population gene and its genotypes. Except the monozygotic twins, and two members of population have different genotypes offsprings of parents are not too much similar, they are different on many aspects such as structural, functional, behavioural and psycological aspects. In long term, micro-evolution leads to formation of new species.

(B) Macro-mutation : A macromutation is a mutation of large phenotypic effect, one that produces a phenotype cell outside the range of variation previously existing in the population. Mutations with effects in early stages of development can have large phenotypic consequences. Macromutation is a mutation that has made a significant impact on population. Eg.- Homoetic mutations of fruitflies.

(C) Chromosonal Mutations or Aberrations: They are changes in the morphology of chromosomes which bring about change in number and sequence of genes over the chromosomes without changing gene structure or ploidy ofthe chromosomes. Changes in chromosomal architecture can be found out either through genetic test or observing the chromosomes after staining, preferably in paired condition. Aberrations are of two types, intrachromosomal and interchromosomal.

(i) Intrachromosomal Modifications : They are aberrations caused by breaking of chromosome segments and their loss or gain within a single chromosome. eg.-deletion, inversion.

(ii) Interchromosomal Modifications : They are chromosonal aberrations which involve two chromosomes causing loss of one and gain of other. e.g.- Duplication, Translocation. 

3. Explain the homologous and Analagous organ?

Ans. – Homologous organs : They are the organs which posses a similar internal structure and similar development, but often have different form and function. The phenomenon of producing functionally different forms from structurally similar structures is called divergent evolution.

eg.- Forelimbs of various tetrapods, whether a frog, lizard, bird, whale, horse or man, have a similar internal structure, similar embryological development and similar types of muscles, nerves and blood vessels. 

Analogous organs : They are organs having similar outward form and function but quite different in anatomy and development. The phenomenon indicates evolution of similar functional structures from unrelated organs. It is called convergent evolution or homoplasty.

eg.- Wings of Insects, Birds and Bats Flipper of penguin and fins of whale. Stings of honeybee and scorpion. Eyes of vertebrate and cephalopod. Analogy in tendrils of different plants. 

4. Write two similarities between male monkeys named as ‘Drayopithecus’ and ‘Rampithecus’.

Ans.- Similarities between “Dryopithecus and Ramapithecus” : 

(i) Both were morphologically similar to chimpanzee.

(ii) They used to walk with bending posture. 

5. Draw a neat diagram of Miller and Very’s experiment.

Ans.

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