cx-ncert-theory-class12-chap06-evolution-en-part04

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Mechanism of Evolution</B></Primary></p>
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<p>What is the origin of this variation and how does speciation occur? Even though Mendel had talked of inheritable ‘factors’ influencing phenotype, Darwin either ignored these observations or kept silence</p>
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<p>In the first decade of twentieth century, Hugo deVries based on his work on evening primrose brought forth the idea of mutations – large difference arising suddenly in a population</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ <span style="color:blue">Mechanism of Evolution</span> $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Mechanism of Evolution</B></Primary></p>
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<p>He believed that it is mutation which causes evolution and not the minor variations (heritable) that Darwin talked about</p>
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<p>Mutations are random and directionless while Darwinian variations are small and directional</p>
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<p>Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation)</p>
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<p>Studies in population genetics, later, brought out some clarity</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ <span style="color:blue">Mechanism of Evolution</span> $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
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<p>Hardy-Weinberg principle stated it using algebraic equations</p>
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<p>This principle says that allele frequencies in a population are stable and is constant from generation to generation</p>
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<p>The gene pool (total genes and their alleles in a population) remains a constant</p>
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<p>This is called genetic equilibrium</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
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<p>Sum total of all the allelic frequencies is 1</p>
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<p>Individual frequencies, for example, can be named p, q, etc</p>
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<p>In a diploid, p and q represent the frequency of allele A and allele a</p>
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<p>The frequency of AA individuals in a population is simply $p^2$</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
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<p>This is simply stated in another ways, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., $p^2$</p>
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<p>Similarly of aa is $q^2$ , of Aa 2pq</p>
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<p>Hence, $p^2$+2pq+$q^2$=1</p>
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<p>This is a binomial expansion of $(p+q)^2$</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
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<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
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<p>When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change</p>
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<p>Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution</p>
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<p>Five factors are known to affect Hardy-Weinberg equilibrium</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
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<p>These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection</p>
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<p>When migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population</p>
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<p>New genes/alleles are added to the new population and these are lost from the old population</p>
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<p>There would be a gene flow if this gene migration, happens multiple times</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
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<p>If the same change occurs by chance, it is called genetic drift</p>
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<p>Sometimes the change in allele frequency is so different in the new sample of population that they become a different species</p>
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<p>The original drifted population becomes founders and the effect is called founder effect</p>
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<p>Microbial experiments show that pre-existing advantageous mutations when selected will result in observation of new phenotypes</p>
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</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Over few generations, this would result in Speciation</p>
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<p>Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave greater number of progeny</p>
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<p>A critical analysis makes us believe that variation due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation</p>
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</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Hardy - Weinberg Principle</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
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<p>Coupled to enhance reproductive success, natural selection makes it look like different population</p>
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<p>Natural selection can lead to stabilisation (in which more individuals acquire mean character value), directional change (more individuals acquire value other than the mean character value) or disruption (more individuals acquire peripheral character value at both ends of the distribution curve) (Figure 6.8).</p>
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</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ <span style="color:blue">Hardy - Weinberg Principle</span> $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>