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” The first day of class should connect to the last day and every day in between!”

Refresh this page every time you arrive!                                                                                                                                                                                                                              This page changes and sometimes many times in the same day.  Its a fluid site. I post what I think we will do and then repost what we accomplish.  Homework posted is to be done at home and not completed days ahead of time.  What is posted ahead is subject to change and may not be updated. There is a sequence that needs to be followed. 

  _________________________________________                                                                                                                                   10/12 – Monday – Columbus Day – “Indigenous People Day”

Columbus discovered America?  But he only made landfall in the Bahamas and Cuba?  Wait didn’t the Vikings make the voyage before he did?  Wait the Chinese mapped out the America’s 70 years before the Viking voyage?  Wait, didn’t native american Indian’s “discover” the America’s first?  Wait wasn’t the America’s already here?!

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Hardy – Weinberg Basics (NOTES) – 

 

Known as the Hardy-Weinberg Principle or the Hardy-Weinberg Equilibrium.

This principle is used to study microevolution – the change in the gene or allele frequencies in a population from one generation to the next.  Specifically microevolution studies if ONE type of allele is changing in frequency from one generation to the next.  Remember that evolution is “decent with modification” through NEW alleles that are selected for based on environmental pressures that develop through mutations.  Mutations are rare and occur slowly through time and thus evolution is a very slow process when it comes to developing NEW alleles in organisms that have long life spans.  MicroEvolution however can occur from one generation to the next if we can exam the frequency (how often) the expressed characteristic (allele) from a single gene changes.  

 

If there is micro evolution than an allele will have a change in its frequency. Frequency is how often that allele exists in a population.  If an allele exists less often (in subsequent populations) the normal distribution for alleles of a single gene will move toward another allele of the same gene that is increasing and establish a new normal distribution.  This is called Direction Selection.

 

When a new normal distribution is established we can “see” this by physical measurements. For example: The Finches significant beak length increases in the Galapagos Islands during a drought.  But with microevolution we can investigate the changes in subsequent populations without “seeing” significant changes that we can physically measure. We can identify the beginning of a shift from the old normal distribution to the new normal distribution with microevolution.

Looking back at out Peppered Moths we can see that the allele for dark wings (melonics) increased with as the melonics were selected for due to the dark colored soot that collected on their natural habitat, which increased their fitness over the light colored moths that were now more susceptible to predators.  Natural selection caused a new normal distribution to occur.  We normally identify evolution AFTER a new normal distribution has been established. With microevolution we can identify exactly when a selective pressure STARTS a change in the frequency of the available alleles for a single gene.

Would we want know if allele frequencies are starting to change if certain alleles are responsible for a disease?

 

How do we know when there is a change in how often an allele in expressed in a population?  Well we have to work from a Null position!  We need to know what to expect if there is no evolution!  This is where Hardy-Weinberg comes in.

 

Mendelian genetics was being argued against in the early 1900’s as some suggested that if Mendelian genetics were true then the dominant allele would eventually “dominate” the population.  The next generation should have more dominant traits than the previous generation yet the frequency of dominant alleles seemed to stay constant from one generation to the next.  It took the work of a mathematician, G.H. Hardy in 1908, to solve the problem and he did so very reluctantly as he though his work was just too simple.  He was taken back how other biologist thought his work was so brilliant. Hardy with a simply derived formula demonstrated that allele frequency will stay constant unless other forces are at play.

 

A German physician,  Wilhelm Weinberg independently also derived the equation in 1908 and thus we call the principle of constant (no change, Null) allele frequencies the Hardy-Weinberg Principle.

 

The forces that can change the allele frequency and thus indicate evolution is occurring are:

 

    1.  Small populations can cause genetic drift or change in allele frequency do to chance events.

         When will a flipping a coin give us frequencies of heads or tails that approximate .5 ?  

         Only in large number of flips. So only in large population size will the chromosome segregate in meiosis in      

         frequencies that approximate 0.5 .  How many small families have all girls or boys if the probabilities to 

         have a boy or girl is about .5?

 

    2.  Selective mating can cause a change in allele frequency if only the males that have certain allele will mate.

          This will cause in increase in fitness of certain males with certain alleles. In our human population we may  

          select who we settle down with but as a population we are not eliminating all males that are tall!!!  

 

    3.   There are mutations occurring.  This would cause new alleles to appear or render old alleles useless for   

           their current application (recessive alleles). The latter would increase the number the recessive allele  

           frequency.  Mutations that occur naturally do so very very infrequently that the chance of themm occuring is  

           very low.  Remember Maize had 4 mutations in about 9,000 years!

 

    4.   There is gene flow in and out of population. If there are individuals of other stable populations that   

            migrate into or out of the population being studied there will be change in allele frequency as other             

            populations are subjected to different selective pressures and thus have different allele frequencies. We call  

            this Gene Flow. If peppered moths that lived closer to the factories in the cities migrated to another area   

            was isolated from factories that population would have an increase in the dark colored wings.

 

    5.    There is Natural Selection Occurring. There is a selective pressure that increases the fitness of   

             individuals that have a certain allele.  In our modern times, especially with modern medicine, people with  

             many illnesses or alleles that would be unfavorable in the “wild” are not selected against anymore.  In the wild it would                    be disadvantageous to be near sighted as we would not have glasses to help us hunt or protect ourselves from predators.  But                if I am not mistaken people who wear glasses have the same fitness as those who do not.

 

So Hardy – Weinberg Principle (Equilibrium) is a formula that predicts the frequencies of alleles in the the next generation, which will be the same as the previous generation, if there is

 

                                                                 1.  Large populations

                                                                 2.  No selective mating

                                                                 3.  No mutations

                                                                 4.  No gene flow

                                                                 5.  No Natural Selection                                                                                                                      

In our modern society these 5 conditions are essentially met and the allele frequency is expected to stay the same.

If there is microevolution occurring  the Hardy – Weinberg formula will act as a baseline to judge against.  

 

We need accurate data from our population to measure against this baseline.  For example what is the current frequency of individuals that have hemophilia (a autosomal recessive disorder)?  

 

What should it be if there is no evolution ——–> Hardy – Weinberg calculations

                                                                                                                                                                                                         

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 FIX NEXT YEAR ! This goes with HW Form 2 that I inadvertently gave before HW Form 1 – Note to myself!!!!

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10/14 – Wednesday – A Day – 4/5A ,7/8A

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– – ____________________________________________________________________                              Jump to: Friday Homework / top    10/16 – Friday – A Day – 4/5A ,7/8A 

Main focus –   

 

a) To identify those factors that contribute to micro evolution and undo the Hardy-Wienberg  equilibrium                                                                                                                                       

 

b) to Take a Hardy – Weinburg Quiz! 

 

 

 

– Natural selection                                                                                                                                                             Directional                                                                                                                                                                                     Disruptive                                                                                                                                                                                       Stabilizing

– Gene Flow

– Genetic Drift

             bottle-neck event

              Founder Effect

-Sexual Selection

-Heterozygote Advantage

-Speciation

             Pre-zygotic barriers

              Post-zygotic barriers 

                                                                                                                  

Period  3/4, 7/8:

 

 1. Hardy – Weinberg Quiz.

2. Lab 3 write-up 

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