10/21 – Wednesday Homework: Hey if you followed me in class just do the form below!
IF I Blew you away today in class please view the 2 videos at the end of Wednesday as I will introduce Hardy – Weinberg Principle in the first and then review the entire packet with you from start to finish (with last years data).
1. Complete the Taster Packet with me with video below if you got lost today.
I completed it in class but will review with the remote students tomorrow.
It is posted below: (This is based on last years data!)
2. Read the Notes below
3. Review the packet’s key based on our data collected Wednesday on Tasting PTC
2 years ago key:
Last years key:
4. Complete Form on the Hardy-Weinberg Principle: DO not start unless you completed 2 & 3.
You will be given three submissions to the form below due by tomorrow morning at 4:30 am.
Please use the following worksheet for the form below:
Evolution 3a- Hardy-Weinberg Principle 2019 .pdf
Hardy-Weinberg Principle Form:
Lecture on the Hardy-Weinberg Principle:
If you are lost on the Hardy-Weinberg Principle then please read the Notes posted below and then read the Hardy – Weinberg Taster Packet. Re- listen to the lecture in class and review the key to the Taster packet.
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 mutation 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
PTC Taster Activity –
Hardy Weinberg Introduction 1 – Micro evolution
Hardy Weinberg Introduction 2 – Taster Activity Packet complete review
End of Wednesday..