POPULATION GENETICS AND THE HARDY-WEINBERG LAW

Hi guys:

This last week we will work in a mathematical model to explain how the evolution has occured. So please watch this video.





And here you have information about this topic. And exercises to develop to get extra point. Use a piece of paper to copy and solve them.

POPULATION GENETICS AND THE HARDY-WEINBERG LAW

1. The Hardy-Weinberg formulas allow scientists to determine whether evolution has occurred. Any changes in the gene frequencies in the population over time can be detected. The law essentially states that if no evolution is occurring, then an equilibrium of allele frequencies will remain in effect in each succeeding generation of sexually reproducing individuals. In order for equilibrium to remain in effect (i.e. that no evolution is occurring) then the following five conditions must be met:
   
   
   1. No mutations must occur so that new alleles do not enter the population.
   2. No gene flow can occur (i.e. no migration of individuals into, or out of, the population).
   3. Random mating must occur (i.e. individuals must pair by chance)
   4. The population must be large so that no genetic drift (random chance) can cause the allele frequencies to change.
   5. No selection can occur so that certain alleles are not selected for, or against.
   Obviously, the Hardy-Weinberg equilibrium cannot exist in real life. Some or all of these types of forces all act on living populations at various times and evolution at some level occurs in all living organisms. The Hardy-Weinberg formulas allow us to detect some allele frequencies that change from generation to generation, thus allowing a simplified method of determining that evolution is occurring. There are two formulas that must be memorized:
   
   

   p² + 2pq + q² = 1 and p + q = 1

   p = frequency of the dominant allele in the population
   q = frequency of the recessive allele in the population
   p² = percentage of homozygous dominant individuals
   q² = percentage of homozygous recessive individuals
   2pq = percentage of heterozygous individuals
   
   Individuals that have aptitude for math find that working with the above formulas is ridiculously easy. However, for individuals who are unfamiliar with algebra, it takes some practice working problems before you get the hang of it. Below I have provided a series of practice problems that you may wish to try out. Note that I have rounded off some of the numbers in some problems to the second decimal place:
   
   
   
   1. PROBLEM #1.You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:
      
      
      1. The frequency of the "aa" genotype.
      2. The frequency of the "a" allele.
      3. The frequency of the "A" allele.
      4. The frequencies of the genotypes "AA" and "Aa."
      5. The frequencies of the two possible phenotypes if "A" is completely dominant over "a."
      
      
   2. PROBLEM #2.Sickle-cell anemia is an interesting genetic disease. Normal homozygous individials (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?
      
      
   3. PROBLEM #3.There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous recessive condition, please calculate the following:
      
      
      1. The frequency of the recessive allele.
      2. The frequency of the dominant allele.
      3. The frequency of heterozygous individuals.
      
      
   4. PROBLEM #4.Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the following:
      
      
      1. The percentage of butterflies in the population that are heterozygous.
      2. The frequency of homozygous dominant individuals.
      
      
   5. PROBLEM #5.A rather large population of Biology instructors have 396 red-sided individuals and 557 tan-sided individuals. Assume that red is totally recessive. Please calculate the following:
      
      
      1. The allele frequencies of each allele.
      2. The expected genotype frequencies.
      3. The number of heterozygous individuals that you would predict to be in this population.
      4. The expected phenotype frequencies.
      5. Conditions happen to be really good this year for breeding and next year there are 1,245 young "potential" Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-sided and how many tan-sided?
      
      
   6. PROBLEM #6.A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is caused by the double recessive genotype, "aa". Calculate allelic and genotypic frequencies for this population.
      
      
   7. PROBLEM #7.After graduation, you and 19 of your closest friends (lets say 10 males and 10 females) charter a plane to go on a round-the-world tour. Unfortunately, you all crash land (safely) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends carry (i.e. are heterozygous for) the recessive cystic fibrosis allele (c). Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?
      
      
   8. PROBLEM #8.You sample 1,000 individuals from a large population for the MN blood group, which can easily be measured since co-dominance is involved (i.e., you can detect the heterozygotes). They are typed accordingly:
      
      

      BLOOD TYPE	GENOTYPE	NUMBER OF INDIVIDUALS	RESULTING FREQUENCY
      M	MM	490	0.49
      MN	MN	420	0.42
      N	NN	90	0.09

      
      Using the data provide above, calculate the following:
      
      
      1. The frequency of each allele in the population.
      2. Supposing the matings are random, the frequencies of the matings.
      3. The probability of each genotype resulting from each potential cross.
      
      
   9. PROBLEM #9.Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the United States. Please calculate the following.
      
      
      1. The frequency of the recessive allele in the population.
      2. The frequency of the dominant allele in the population.
      3. The percentage of heterozygous individuals (carriers) in the population.
      
      
   10. PROBLEM #10.In a given population, only the "A" and "B" alleles are present in the ABO system; there are no individuals with type "O" blood or with O alleles in this particular population. If 200 people have type A blood, 75 have type AB blood, and 25 have type B blood, what are the alleleic frequencies of this population (i.e., what are p and q)?
       
       
   11. PROBLEM #11.The ability to taste PTC is due to a single dominate allele "T". You sampled 215 individuals in biology, and determined that 150 could detect the bitter taste of PTC and 65 could not. Calculate all of the potential frequencies.
       
   See you!!!

POPULATIONS ECOLOGY

Hi guys:

This week we will work on Population ecology, so please....

1. Print and read the following worksheet in pairs:

WORKSHEET ON POPULATION ECOLOGY

2. Watch this video and bring questions to the class!!!




See you at class!!!!

DICHOTOMOUS KEY LAB

Hi guys:

This week we will work in a dichotomous key design, so please, follow the instructions here.

Print this worksheet and bring it to class.

DICHOTOMOUS KEY LAB

First of all, use the video to feed your Theoretical Framework.




Secondly, red the following passage to start your understanding about the topic:

Background Information

A dichotomous key is a tool that allows the user to determine the identity of items and organisms in the natural world. It is the most widely used form of classification in the biological sciences because it offers the user a quick and easy way of identifying unknown organisms. Keys consist of a series of choices that lead the user to the correct name of a given item. “Dichotomous” means “divided into two parts.” That is why dichotomous keys always give two choices in each step. In each step, the user is presented with two statements based on characteristics of the organism. If the user makes the correct choice every time, the name of the organism will be revealed at the end.

There are two kinds of descriptions that might be presented to the user of a dichotomous key: qualitative and quantitative descriptions. Qualitative descriptions concern the physical attributes, or qualities, of the item being classified. Examples of qualitative descriptions are such phrases as “contains green striations on top surface” or “feels slick on bottom surface.” Quantitative descriptions concern values that correspond with the item being classified. Examples of quantitative descriptions are such phrases as “has 10 striations on top surface,” “has 8 legs,” or “weighs 5 grams”. Knowing the difference between these two types of descriptions can be immensely beneficial for creators and users of dichotomous keys.

There are two ways to set up a dichotomous key. One way is to present the two choices together, and the other way is to group by relationships. When the dichotomous key is set up by presenting the two choices together, it is easy to distinguish between them. However, relationships between various characteristics are not emphasized. When the dichotomous key is grouped by relationships, the choices are separated, yet it is easy to see the relationships between them. While this method may prove to be more difficult to construct, many users prefer it because it gives them more information.

Taken from: http://www.laseagrant.org/education/lessons/halfshell/creating-key/

SEE YOU AT CLASS!!!

TAXONOMY

Hi guys:

This week we will work on Taxonomy general aspects, definitions and nomenclature.

Bring squared paper, scissor and glue.

Here it is the ppt presentation for the class.

PPT ON TAXONOMY

And here the worksheets, you can print this in pairs.

cutouts for chromosome comparison

Worksheet for chromosome comparison

Watch this video at home




See you at class!!!

EVOLUTIONARY HISTORY

Hi guys:

This week we will connect the evolution theory to the biological and geographical events that produce different types of life, all along the earth´s history with life living in.

First print the worksheet in the following link and bring it to class.

https://drive.google.com/file/d/1zSKu0C-S8zNT9V8cBBsl8F2py-Qoc6p9/view?usp=sharing

Second, watch this video and take notes in your notebook to get extra points






See you at class!!!

CLADOGRAMS AND PHYLOGENY

Hi students, welcome to the Third Term.

This first week we will work on classification aspects related to the evolution of the different characteristics that belong to an specific group.

Print this worksheet individually and bring it to the first class of the second week.

Worksheet on cladograms

Watch this video, we will have a short quiz about it, to get extra points




See you at class!!!!

NATURAL SELECTION AND TYPES OF EVOLUTION

Hi Guys:

This week we will work on Natural selection concepts and types of Evolution.

So please, print the following worksheet.

Types of Evlolution worksheet

Watch the video and take notes or write questions about what you didn´t understand

And read this nformation, take note in your notebook to get extrapoints

Types of Evolution

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Evolution over time can follow several different patterns. Factors such as environment and predation pressures can have different effects on the ways in which species exposed to them evolve. shows the three main types of evolution: divergent, convergent, and parallel evolution.

Figure%: Types of evolution; a)divergent, b)convergent, and c)parallel.

Divergent Evolution

When people hear the word "evolution," they most commonly think of divergent evolution, the evolutionary pattern in which two species gradually become increasingly different. This type of evolution often occurs when closely related species diversify to new habitats. On a large scale, divergent evolution is responsible for the creation of the current diversity of life on earth from the first living cells. On a smaller scale, it is responsible for the evolution of humans and apes from a common primate ancestor.

Convergent Evolution

Convergent evolution causes difficulties in fields of study such as comparative anatomy. Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure. For example, whales and fish have some similar characteristics since both had to evolve methods of moving through the same medium: water.

Parallel Evolution

Parallel evolution occurs when two species evolve independently of each other, maintaining the same level of similarity. Parallel evolution usually occurs between unrelated species that do not occupy the same or similar niches in a given habitat.

Problems >> 

Problem : On his voyage with the Beagle, Charles Darwin carefully studied several species of finches. He found that many had come from a single species, but they had adapted to their environment by choosing different food sources and developing radically different beak designs to match their choice of food. What pattern of evolution did the finches show?

The finches showed divergent evolution. As time passed, the different species adapted to their own lifestyles and became more and more different from the other closely related species.

Problem : Many species of owls hunt only at night. These winged predators have evolved extremely sensitive hearing to help track insects and other prey. Another night hunting winged predator, the bat also has extremely sensitive hearing to track prey in the dark. What pattern of evolution does this show?

This is an example of convergent evolution. Owls (birds) and bats (mammals) are not closely related, but both have evolved similar traits (flight and good hearing) to help them fill the same role as night hunters.

Problem : Imagine two types of ancient forest animals: a goat-like grazing animal and a small ground-dwelling rodent that lives on insect prey. At the same time, these two animals leave the forest and begin living in grassy plains. The rodent evolves large powerful claws for digging burrows to hide in, while the grazer develops long legs for running from predators. What type of evolution does this show?

This is an example of parallel evolution. The two animals were fairly dissimilar to begin with. They filled different roles in the forest environment. When they moved to the plains, both animals evolved to adapt to the new environment, but they did not become any more or less similar to each other.

Problem : What difficulty does convergent evolution pose for evolutionary biologists?

The major difficulty involved with convergent evolution is the formation of analogous structures. These structures may appear similar and perform similar functions, making it seem that two species are closely related. However, analogous structures develop from different ancestral structures and do not indicate close relationships.

Coevolution 

Just as no man is an island, neither is any bird, insect, plant, or mammal. Many species live in close relationships with others, affecting each others ways of life. It seems logical to think that species that live closely with each other might evolve in adaptation to each other. This logic is extremely difficult to prove, since it requires direct proof of evolution in not one but two species. However, there is ample evidence to suggest that coevolution does take place.

Coadaptation

In order to live in symbiotic or parasitic relationship, species must be adapted to each other. For example, cattle harbor bacteria in their stomachs that help them break down plant material. To live like this, the immune system of the cattle must be adapted to not kill these useful bacteria and the bacteria themselves must be adapted to live in the harsh environment of the cow's stomach. If a population of cattle moved to a new location where radically new plant material was available, they might adapt to eating this new food source. The bacteria, in turn, might then undergo adaption of their own digestive mechanisms to the new plant material. This would be an example of coadaptation. Most biologists accept coevolution on the basis of coadaptation if there is no overwhelming evidence to the contrary.

Coevolutionary Arms Races

In parasitic relationships, the prey species often evolves mechanisms to defend itself against the parasite. However, the parasite may also evolve to evade these new mechanisms. This back-and-forth evolution of defense and offense, often called a coevolutionary arms race, can often result in a rapid burst of evolutionary change in both species.

Problems

Problem : Describe a coevolutionary arms race.

A coevolutionary arms race takes place in a predator-prey relationship when the prey evolves a new defense or the predator evolves a new offense. Each species will evolve a new trait to give them an advantage over the other. When this process occurs with several new adaptations over a short period of time, it is known as a coevolutionary arms race.

Problem : Why is coevolution difficult to prove?

Coevolution is difficult to prove because it requires direct evidence of not one but two species evolving together.

Problem : What do most biologists accept as evidence for coevolution?

Most biologists will accept coadaptation as proof of coevolution in the absence of evidence to the contrary.

Problem : What might be another explanation of coadaptation?

Coadaptation may arise from coevolution, the development of traits in two species in direct relation to each other. However, coadaptation may also occur as a result of two species developing traits independently of each other that then happen to make the species well adapted to each other.

Taken from:

SparkNotes Editors. (n.d.). SparkNote on Patterns of Evolution. Retrieved August 5, 2018, from http://www.sparknotes.com/biology/evolution/patternsofevolution/

Punctuated equilibrium Punctuated equilibrium is an important but often-misinterpreted model of how evolutionary change happens. Punctuated equilibrium does not: Suggest that Darwin's theory of evolution by natural selection is wrong. Mean that the central conclusion of evolutionary theory, that life is old and organisms share a common ancestor, no longer holds. Negate previous work on how evolution by natural selection works. Imply that evolution only happens in rapid bursts. Punctuated equilibrium predicts that a lot of evolutionary change takes place in short periods of time tied to speciation events. Here's an example of how the model works: Stasis: A population of mollusks is experiencing stasis, living, dying, and getting fossilized every few hundred thousand years. Little observable evolution seems to be occurring judging from these fossils. Isolation: A drop in sea level forms a lake and isolates a small number of mollusks from the rest of the population. Strong selection and rapid change: The small, isolated population experiences strong selection and rapid change because of the novel environment and small population size: The environment in the newly formed lake exerts new selection pressures on the isolated mollusks. Also, their small population size means that genetic drift influences their evolution. The isolated population undergoes rapid evolutionary change. This is based on the model of peripatric speciation. No preservation: No fossils representing transitional forms are preserved because of their relatively small population size, the rapid pace of change, and their isolated location. Reintroduction: Sea levels rise, reuniting the isolated mollusks with their sister lineage. Expansion and stasis: The isolated population expands into its past range. Larger population size and a stable environment make evolutionary change less likely. The formerly isolated branch of the mollusk lineage may out-compete their ancestral population, causing it to go extinct. Preservation: Larger population size and a larger range move us back to step 1: stasis with occasional fossil preservation. This process would produce the following pattern in the fossil record: Evolution appears to happen in sharp jumps associated with speciation events. We observe similar patterns in the fossil records of many organisms. For example, the fossil records of certain foraminiferans (single-celled protists with shells) are consistent with a punctuated pattern. Scanning electron micrograph of a foraminiferan Howev