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.

http://commons.wikimedia.org/wiki/File:Laurelyhardy_179.jpghttp://www.flickr.com/photos/shoot-art/3921390861/http://www.flickr.com/photos/rietje/76575482/sizes/m/in/photostream/

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:

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

Online practise

questions

And more practise

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