ib biology option d.4: hardy weinberg principle
DESCRIPTION
Course materials for option D.4 of The IB Biology CourseTRANSCRIPT
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
http://www.flickr.com/photos/west-park/2610430399/
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
http://commons.wikimedia.org/wiki/File:Hardy-Weinberg.svg
An interactive that charts the changes in frequency and represents them as areas:
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
This graph of the of relative frequencies generated by an also be used to read off the values for the allele and gene frequencies
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?
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
For the equation to work mathematically:- The organism involved must be diploid
and reproduce sexually- Generations must not overlap- The trait must be autosomal
Online QuizFurther information:
Good video Also revises directional selection:
Salman Khan explains HWE