ib biology option d.4: hardy weinberg principle
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Course materials for option D.4 of The IB Biology CourseTRANSCRIPT
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IB BiologyOption D
D4 The Hardy Weinberg Principle
Jason de Nys
All syllabus statements ©IBO 2007All images CC or public domain or link to original material.
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The Hardy–Weinberg principle states that both allele and genotype frequencies in a population remain constant
—that is, they are in equilibrium—from generation to generation unless specific disturbing influences are introduced. Wikipedia
D4.1 Explain how the Hardy-Weinberg equation is derived
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Consider two alleles A and a
A has a frequency of pa has a frequency of q Therefore p + q = 1
As the two alleles are the only options at that locus
Lets make a Punnet square:
Hence:
http://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_principle
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http://commons.wikimedia.org/wiki/File:Hardy-Weinberg.svg
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An interactive that charts the changes in frequency and represents them as areas:
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D4.2 Calculate allele, genotype and phenotype frequencies for two allelles of a gene, using the Hardy-Weinberg equation
Allele and genotype frequencies can be calculated using the previously mentioned equations:
and
Example: An estimated 10% of people are left handed. That is a phenotypic frequency of 0.1.They are homozygous for the recessive allele for handedness
Hence:
Since , Therefore the frequency of the dominant allele will be Or 68%
Online practise
questions
And more practise
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This graph of the of relative frequencies generated by an also be used to read off the values for the allele and gene frequencies
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D4.3 State the assumptions made when the Hardy Weinberg equations is used
Okay, so if:
“both allele and genotype frequencies in a population remain constant—that is, they are in equilibrium—from generation to generation”
What must be the underlying assumptions?
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Basic Assumptions of the Hardy-Weinberg Principle- All phenotypes equal fitness, no natural selection- No mutation- No immigration or emigration- No genetic drift (infinitely large population)- No assortative mating Of course, at least one of
these factors will be acting on a population in the wild
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For the equation to work mathematically:- The organism involved must be diploid
and reproduce sexually- Generations must not overlap- The trait must be autosomal
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Online QuizFurther information:
Good video Also revises directional selection:
Salman Khan explains HWE