Hardy-Weinberg equilibrium

1 / 16

Hardy-Weinberg equilibrium - PowerPoint PPT Presentation

Hardy-Weinberg equilibrium. if p = frequency of allele A q = frequency of allele a p + q = 1, ( p + q ) 2 = 1 p 2 + 2pq + q 2 = 1 if only law of probability affects the frequency w/ which gametes combine to form new individuals. Bisexual population

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

PowerPoint Slideshow about 'Hardy-Weinberg equilibrium' - kamaria

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Hardy-Weinberg equilibrium
• if p = frequency of allele A

q = frequency of allele a

• p + q = 1, ( p + q )2 = 1
• p2 + 2pq + q2 = 1
• if only law of probability affects the frequency w/ which gametes combine to form new individuals
Bisexual population
• Large population
• Random mating
• No mutation
• Migration ~ 0
• Natural selection does not affect the locus
A population that is in Hardy-Weinberg equilibrium will experience no change in either genotype frequency or allele frequency
• If one or more of the conditions is violated, genotype frequency and allele frequency will change
Example
• If only 6% of the population displays pale eyes (recessive gene e). What is the frequency of genotype Ee in this population?

q2 = 0.06 ---> q = 0.24

p + q = 1 ---> p = 0.76

Ee = 2pq = 2(0.76)(0.24) = 0.36

Genetic variation
• Cline – a measurable, gradual change over a geographical region in the average of some phenotype character
• Ecotype – abrupt changes in the phenotype characters within a species, which often reflect abrupt changes in local environment
Geographic isolates – semi-isolated populations prevented by some extrinsic barriers from a free flow of genes
• Genetic polymorphism – the existence within a species or population of different forms of individuals
Maintenance of balanced polymorphism

(vs. transitional or directional polymorphism)

• heterosis
• diversifying evolution
• frequency-dependent selection
• selective forces operating in different directions within different patches of a fine mosaic in the population
• Speciation
• Allopatric speciation
• Sympatric speciation
Isolation mechanism
• Pre-zygotic: habitat, temporal, ethological, mechanical
• Post-zygotic
• hybrid inviability or weakness
• hybrid sterility
• F2 breakdown
Reduction in variation
• inbreeding, bottlenecks, founder effect, genetic drift
• genetic drift - random shifts in allele frequencies
Effect of small populations
• More demographic variation, inbreeding depression, genetic drift → higher risk of extinction

Minimum viable population size

• the threshold # of individuals that will ensure the persistence of subpopulation in a viable state for a given time interval
Effective population size (Ne)
• the size of a genetically idealized population with which an actual population can be equated genetically, Ne = N , if
• equal sex ratio
• equal probability of mating
• constant dispersal rate
• progeny per family randomly distributed
unequal sex ratio

Ne = 4 Nm˙Nf / (Nm + Nf )

• population fluctuation

1 / Ne = (1 / t )(1/N1 + 1/N2 + … + 1/Nt)

• non-random progeny distribution

Nk

Ne = -----------------------------------------

(N/N-1)˙Vk/k˙(1+F) + (1-F)

Effect of continental drift
• Distribution/radiation of monotremes and marsupials
Extinction and its causes
• Natural causes: climatic changes and stochastic event
• Human disturbance
• habitat alteration
• over-exploitation
• exotic species
• diseases and other factors