biology-class-12-unit-08-chapter-01-genetics-and-evolution-evolution-l-2-3-uaehdhfdejy

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> What is natural selection? </primary>
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- It is the process whereby organisms better adapted to their environment tend to survive and produce more offspring

- Why are certain organisms better adapted?
 - Due to variations which are inheritable and provide survival advantage

- How does these variations occur?
 - Sexual reproduction leading to recombination during meiosis
 - Prolonged exposure to ionising radiations
 - Other atmospheric changes that produce changes either in genes/chromosomes or the germplasm

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<footer style = "font-size: 18px">Evolution $\rightarrow$ Biological evolution $\rightarrow$ <span style = "color:blue"> What is natural selection? </span> $\rightarrow$ 4 major postulates of the theory of natural selection $\rightarrow$ Biological Evolution by Natural Selection </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> 4 major postulates of the theory of natural selection </primary>
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- Individuals in a population have variations which can be passed to the next generation
- There is struggle for existence due to limited resources present in nature.
- Survival of the fittest: Only such organisms will survive which exhibit variations which render survival advantage
- Reproductive fitness:
 - More young ones are produced than can survive
 - Fitness is the end result of the ability to adapt and get selected by nature

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<footer style = "font-size: 18px">Biological evolution $\rightarrow$ What is natural selection? $\rightarrow$ <span style = "color:blue"> 4 major postulates of the theory of natural selection </span> $\rightarrow$ Biological Evolution by Natural Selection $\rightarrow$ Evidences for evolution </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Biological Evolution by Natural Selection </primary>
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<footer style = "font-size: 18px">What is natural selection? $\rightarrow$ 4 major postulates of the theory of natural selection $\rightarrow$ <span style = "color:blue"> Biological Evolution by Natural Selection </span> $\rightarrow$ Evidences for evolution $\rightarrow$ Evidences from palaentology </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Evidences for evolution </primary>
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- **Question** Is Evolution real? How do we know it?

- The evidences for evolution has come from various sources-
* Palaentology
* Morphology and comparative anatomy
* Embryology
* Biochemistry
* Connecting links
* Missing links
* Direct Observation of evolutionary processes
* Anthropogenic Evolution

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<footer style = "font-size: 18px">4 major postulates of the theory of natural selection $\rightarrow$ Biological Evolution by Natural Selection $\rightarrow$ <span style = "color:blue"> Evidences for evolution </span> $\rightarrow$ Evidences from palaentology $\rightarrow$ Evidences from palaentology </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Evidences from morphology & anatomy </primary>
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- **Homologous organs**

- Organs having common origin and built on same fundamental pattern, but perform different functions and have different appearance
 - These structures are obtained from a common ancestor and show evolutionary relatedness
 - Example - Structure of brain is similar from fishes to mammals

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<footer style = "font-size: 18px">Evidences from palaentology $\rightarrow$ Fossils $\rightarrow$ <span style = "color:blue"> Evidences from morphology & anatomy </span> $\rightarrow$ Analogous organs $\rightarrow$ Divergent evolution </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Divergent evolution </primary>
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- Also called adaptive radiation

- The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography

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<footer style = "font-size: 18px">Evidences from morphology & anatomy $\rightarrow$ Analogous organs $\rightarrow$ <span style = "color:blue"> Divergent evolution </span> $\rightarrow$ Adaptive radiation of marsupials of Australia $\rightarrow$ Convergent evolution </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Adaptive radiation of marsupials of Australia </primary>
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- It give rise to homologous structures

- Provides strong evidence in favour of organic evolution
- Example Limb structure in mammals

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<footer style = "font-size: 18px">Analogous organs $\rightarrow$ Divergent evolution $\rightarrow$ <span style = "color:blue"> Adaptive radiation of marsupials of Australia </span> $\rightarrow$ Convergent evolution $\rightarrow$ Convergent evolution </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Convergent evolution </primary>
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- **Convergent evolution** is the process where organisms not closely related, independently **evolve** similar traits as a result of having to adapt to similar environments

- **When more than one adaptive radiation occur in an isolated geographical area, it is called Convergent evolution or adaptive convergence**

- It leads to analogy

- **Also known as parallel evolution**

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<footer style = "font-size: 18px">Divergent evolution $\rightarrow$ Adaptive radiation of marsupials of Australia $\rightarrow$ <span style = "color:blue"> Convergent evolution </span> $\rightarrow$ Convergent evolution $\rightarrow$ Convergent evolution </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Convergent evolution </primary>
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- The Process by which two lines of evolutionary development bring about superficially similar creatures when different groups of organism are subjected to the same environmental selection pressures,they tend to evolve similar design features

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<footer style = "font-size: 18px">Convergent evolution $\rightarrow$ Convergent evolution $\rightarrow$ <span style = "color:blue"> Convergent evolution </span> $\rightarrow$ Vestigial organs $\rightarrow$ Evidences from embryology </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Connecting links </primary>
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- **Peripatus** Connecting link between annelida and arthropoda

- **Missing links** Transitional fossil forms showing characteristics of two different groups of living animals

- **Seymoria** missing link between amphibian and reptile

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<footer style = "font-size: 18px">Evidences from biochemistry $\rightarrow$ Connecting links $\rightarrow$ <span style = "color:blue"> Connecting links </span> $\rightarrow$ Connecting links $\rightarrow$ Direct observation </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Connecting links </primary>
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- **Missing Links** Transitional fossil forms showing characteristics of two different groups of living animals

- **Archaeopteryx** missing link between reptile and bird

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<footer style = "font-size: 18px">Connecting links $\rightarrow$ Connecting links $\rightarrow$ <span style = "color:blue"> Connecting links </span> $\rightarrow$ Direct observation $\rightarrow$ Artificial breeding in dogs </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Direct observation </primary>
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- **Artificial Breeding Programme/Hybridisation**

* Man has bred selected plants and animals for agriculture and horticulture

* Domestication of wild varities has also been done

* The intensive breeding programme has created breeds that
- differ from other breeds but still are of same group/species

* What does this suggest?

* If within hundreds of years, man could create new breeds, could not nature have done the same over millions of years?

- **Evolutionary change in beak shape of Darwin's finches have been observed**

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<footer style = "font-size: 18px">Connecting links $\rightarrow$ Connecting links $\rightarrow$ <span style = "color:blue"> Direct observation </span> $\rightarrow$ Artificial breeding in dogs $\rightarrow$ Direct observation </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Anthropogenic evolution </primary>
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* Industrial Melanism is one example of man made or anthropogenic evolution

* Before Industrialisation → more white winged moths were present

* After Industrialisation → more dark winged moths were observed

* What had happened?

* Before Industrialisation → tree trunks were light, thick growth of white lichen over the trunk, easy for white moth to camouflage

* After Industrialisation → smoke and soot from Industries made barks dark in colour, lichens do not grow in polluted areas, dark winged moth or melanic moth could easily camouflage

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<footer style = "font-size: 18px">Artificial breeding in dogs $\rightarrow$ Direct observation $\rightarrow$ <span style = "color:blue"> Anthropogenic evolution </span> $\rightarrow$ Anthropogenic evolution $\rightarrow$ Let's discuss </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Let's discuss </primary>
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* Is it possible to have chemical evolution of life in the present conditions of earth?

* No, it is not possible to have chemical evolution of new living forms today because the environmental conditions prevalent then and now has undergone sea change.

* The primitive earth had conditions suitable to initiate chemical evolution of life as evident from Miller & Urey's Experiment

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![image](/subject-images/iitpal/image/biology-class-12-unit-08-chapter-01-genetics-and-evolution-evolution-l-2_3-uaehdhfdejy-124-2890.8.jpg)

![image](/subject-images/iitpal/image/biology-class-12-unit-08-chapter-01-genetics-and-evolution-evolution-l-2_3-uaehdhfdejy-22.jpg)

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<footer style = "font-size: 18px">Anthropogenic evolution $\rightarrow$ Anthropogenic evolution $\rightarrow$ <span style = "color:blue"> Let's discuss </span> $\rightarrow$ Let's discuss $\rightarrow$ Let's discuss </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Let's discuss </primary>
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- Do you agree that the rate of appearance of new forms is linked to the life cycle or life span of an organism How?

* Yes

* We know that new forms arises out of the reproductive fitness gained from inherited advantageous variations (Natural Selection)

* And in due course of time, the variant population outgrows the other forming a new species altogether over a period of time (speciation)

* Organisms having shorter life span will show new forms within days as in bacteria. For the same thing to happen in fishes or fowls would take millions of years as their life spans are in years

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<footer style = "font-size: 18px">Anthropogenic evolution $\rightarrow$ Let's discuss $\rightarrow$ <span style = "color:blue"> Let's discuss </span> $\rightarrow$ Let's discuss $\rightarrow$ Let's discuss </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Let's discuss </primary>
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- **Differences between Darwinian variation and Hugo de vries's Mutation**

| Natural selection| |Mutation| |
| -------- | -------- | -------- | -------- |
| Variations are small and directional| |Mutations are random and directionless| 
| Evolution is gradual|| Single step large mutation called Saltation||  |

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<footer style = "font-size: 18px">Let's discuss $\rightarrow$ Let's discuss $\rightarrow$ <span style = "color:blue"> Let's discuss </span> $\rightarrow$ Let's discuss $\rightarrow$ Let's summarize </footer>

### <Success style="font-size:25px"> Genetics And Evolution Evolution L-2 </Success>
### <primary style="font-size:24px"> Let's summarize </primary>
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- **Today we learnt about**

* Biological evolution by Natural Selection

* Postulates of theory of Natural Selection

* Evidences for evolution

* Palaentology

* Morphology and comparative anatomy

* Embryology

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<footer style = "font-size: 18px">Let's discuss $\rightarrow$ Let's discuss $\rightarrow$ <span style = "color:blue"> Let's summarize </span> $\rightarrow$ Let's summarize $\rightarrow$ Let's reflect </footer>