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# IB Biology Option D.4: Hardy Weinberg Principle

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Course materials for option D.4 of The IB Biology Course

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### IB Biology Option D.4: Hardy Weinberg Principle

1. 1. http://commons.wikimedia.org/wiki/File:Laurelyhardy_179.jpg<br />http://www.flickr.com/photos/shoot-art/3921390861/<br />http://www.flickr.com/photos/rietje/76575482/sizes/m/in/photostream/<br />IB Biology<br />Option D<br />D4 The Hardy Weinberg Principle<br />Jason de Nys<br />All syllabus statements ©IBO 2007<br />All images CC or public domain or link to original material.<br />
2. 2. D4.1 Explain how the Hardy-Weinberg equation is derived<br />The Hardy–Weinberg principle states that both allele and genotype frequencies in a population remain constant<br />—that is, they are in equilibrium—from generation to generation unless specific disturbing influences are introduced. Wikipedia<br />http://www.flickr.com/photos/west-park/2610430399/<br />
3. 3. Consider two alleles A and a<br />A has a frequency of p<br />ahas a frequency of q<br />Therefore p + q = 1<br />As the two alleles are the only options at that locus<br />Lets make a Punnet square:<br />Hence: 𝒑𝟐+𝟐𝒑𝒒+𝒒𝟐=𝟏<br /> <br />http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle<br />
4. 4. http://commons.wikimedia.org/wiki/File:Hardy-Weinberg.svg<br />
5. 5. An interactive that charts the changes in frequency and represents them as areas:<br />
6. 6. D4.2 Calculate allele, genotype and phenotype frequencies for two allelles of a gene, using the Hardy-Weinberg equation <br />Allele and genotype frequencies can be calculated using the previously mentioned equations:<br />𝒑+𝒒=𝟏<br />and<br />𝒑𝟐+𝟐𝒑𝒒+𝒒𝟐=𝟏<br /> <br />Example: An estimated 10% of people are left handed. That is a phenotypic frequency of 0.1.<br />They are homozygous for the recessive allele for handedness<br />Hence: 𝑞2=0.1<br />∴𝑞=0.1<br />∴𝑞≅0.32<br />Since 𝑝+𝑞=1,𝑝=1−𝑞<br />Therefore the frequency of the dominant allele will be 1−0.32=0.68<br />Or 68%<br /> <br />Online practise questions<br />And more practise<br />
7. 7. This graph of the of relative frequencies generated by 𝒑𝟐+𝟐𝒑𝒒+𝒒𝟐=𝟏 can also be used to read off the values for the allele and gene frequencies <br /> <br />
8. 8. D4.3 State the assumptions made when the Hardy Weinberg equations is used<br />Okay, so if:<br />“both allele and genotype frequencies in a population remain constant—that is, they are in equilibrium—from generation to generation”<br />What must be the underlying assumptions?<br />
9. 9. Basic Assumptions of the Hardy-Weinberg Principle<br /><ul><li>All phenotypes equal fitness, no natural selection
10. 10. No mutation
11. 11. No immigration or emigration
12. 12. No genetic drift (infinitely large population)
13. 13. No assortative mating</li></ul>Of course, at least one of these factors will be acting on a population in the wild<br />
14. 14. For the equation to work mathematically:<br /><ul><li>The organism involved must be diploid and reproduce sexually
15. 15. Generations must not overlap
16. 16. The trait must be autosomal</li></li></ul><li>Further information:<br />Online Quiz<br />Good video Also revises directional selection:<br />Salman Khan explains HWE<br />