Module 8 Population Genetics

Concept Organizer

Module Descriptions

There are two modules in Unit D: Module 8 and Module 9. In Module 8, you will explore the genetics of populations and how we can quantitatively measure how populations have changed. You will also investigate how many factors can interact to cause populations to evolve or remain stable. Module 9 is divided into two sections: section 9.1 and section 9.2. In Section 9.1, the emphasis is on describing the relationships that exist between organisms, the mechanisms that organisms use to protect themselves from each other, and how the species make-up of communities change over time in the process of succession. In Section 9.2, the emphasis is on how population size and changes can be measured, interpreted, and the results of the studies applied to the control of population growth. Together these modules will allow you to better understand how both an individual’s contributions to the gene pool and the interactions within communities result in change over time.

By studying this unit you will be able to:

• explain how populations can change over time
• describe the ways that members of a population interact with each other and with members of other populations
• analyze quantitatively how populations change over time
• analyze the technologies used by society in controlling and managing populations

The Unit D assessment follows the Diploma exam format, with a multiple-choice section and a written response question. Information from both Module 8 and both sections of Module 9 will be incorporated into the exam.

Module 8: Populations, Individuals, and Gene Pools

In Module 8 you will be introduced to the gene pool, and you will learn how to quantify its make-up, determine whether it is changing, and determine what factors lead to this change. You will be asked to apply your knowledge to answer the following questions: What are the factors and conditions that exist when individuals in a population can change the gene pool? How can we analyze the effects of these factors?

Module 9: Section 1—Ecological Interactions

In Module 9.1 you will look at how the interactions and symbiotic relationships between organisms affect the structure of populations and communities. You will also examine defense mechanisms that organisms use to survive predation and competition. Lastly, you will study the concept of succession, and how the species that make up communities change over time. By the end of module 9.1, you should be able to discuss the relationships that exist between species and ecosystems, and the effects that these interactions have on population changes.

Module 9: Section 2—Measuring, Interpreting, and Analyzing Changes in Populations

In Module 9.2, the focus is on population growth. Here you will learn what factors contribute to growth, and how growth within populations is measured. As part of your studies you will learn about the two major types of growth patterns and the two strategies used by organisms for maximizing growth of populations. Upon completion of module 9.2, you should be able to discuss how biologists measure, interpret, and analyze the changes in populations over time.

Big Picture

Cheetahs, the fastest of all land animals, have had a rapid loss of variation in their gene pools. Examination of 52 different gene loci has failed to show any polymorphisms (more than one allele). The lack of genetic variability is so profound that cheetahs will accept skin grafts from each other, just as identical twins do. Whether a population with this little genetic diversity can adapt in a changing environment remains to be seen.

This loss of diversity, an increasingly common scenario in this time of rapid environmental change, holds the potential for extinction. The ability to accurately measure the degree of genetic diversity is critical. In this module, we will look at the work of two geneticists who have given us the mathematical tools to easily, but accurately, measure the degree of genetic diversity in a population. The same tool allows us to predict whether a population is stable (in equilibrium), or evolving in response to a change in the environment. 

Over a period of time, individuals in a population contribute to the gene pool, resulting in changes to the composition of the populations of their communities.  The important thing to grasp is that gene pool change is normal for all populations on this planet as environments change. The concerning issue is whether the changes we are currently seeing are due to the natural mechanisms of evolution or due to environmental changes caused by our species. The other important point is the rate of change, in that adaptation (movement of allele frequencies towards more adapted forms) takes many generations. With the current rate of environmental change produced by human activity, there may not be adequate time for favorable alleles to replace those that are ill suited to new environments – the result can be (and has been for many species to date) extinction. Perhaps the most important question worth thinking about as a result of your studies in this module is whether having the skills and knowledge to calculate genetic change and predict the effect of our actions on gene pools obliges us to change our ways and prevent further disruption.   

Essential Questions

In this Module you will explore the following essential questions:

1. What are the factors and conditions that exist when individuals in a population can change the gene pool?
2. How can we analyze the effect of these factors?

In This Module

 Lesson 1: Hardy Weinberg Theory

This lesson is split into Part A and Part B. Part A introduces the concept of the gene pool and frequency, and describes how frequencies are defined and calculated. Part B goes on to address the following focusing questions:

• What are the five conditions of the Hardy-Weinberg principle that affect the frequency of alleles in a population?
• What happens when conditions of the Hardy-Weinberg principle are not met?

Lesson 2: Causes of Change in the Gene Pool

• What factors cause changes in diversity in the composition of the gene pool?

Lesson 3: Hardy-Weinberg Calculations

• How can you mathematically determine the allele and genotype frequencies for populations?
• How are the Hardy Weinberg equations used to determine whether a population is undergoing change?

Lesson 4: Human Activity and Gene Pool Change

• What are the intended and unintended consequences of human activities on gene pools?

Lesson 4.8.1

Lesson 1: Part A—The Gene Pool

Get Focused

Although up to now we’ve focused on how individuals come to inherit their genes, we now shift our attention and remind ourselves that each living organism, whether human, Amoeba, or pine tree, is part of a functioning population in nature. Individuals have no power to adapt or evolve, but populations do. As a general rule, the more genetic variation (polymorphism) there is in a population, the better the chance of at least some individuals surviving if unfavorable environmental change occurs. We can say, then, that variation helps protect species from extinction. However, how do biologists know how much variation exists in a population? 

By the end of this lesson you should be able to answer the following focusing question:

• How do biologists quantitatively describe the variation within a population?

Module 8: Lesson 1 Assignment

You will complete an assignment on frequency calculation and an assignment on determining frequencies for assessment. When you have completed the lesson you can then complete the online assignment Bio30 4.8.1 online assignment

 The other questions in this lesson are not marked by the teacher; however, you should still answer these questions. The Self-Check and Try This questions are placed in this lesson to help you review important information and build key concepts that may be applied in future lessons.

4.8.1 page 2

Explore

When we’re interested in the genetic composition of a population, we’re interested in its gene pool.

What's in a gene pool? Imagine if all individuals in the human species threw their two alleles for each of their 30,000 genes into a large basket. That basket represents the human gene pool—it is an inventory of all the genes in that population. How many alleles would be in the gene pool of the entire human population?

            30,000 genes  X  2 alleles/gene  X  7 billion people = __?___alleles

Fortunately, in Population Genetics we generally only deal with one trait or gene at a time, and with much smaller populations!

Describing Gene Pools

Consider a population of only 10 field mice in a specific region of the southern Alberta prairies. Mice have two different alleles for coat color, black (B) and white (b). The mice are pictured below with their genotypes:

Imagine that each mouse can throw their two alleles for coat color into a basket.  This is the gene pool.  The gene pool can be described in three ways:

• by its genotype frequencies
• by its phenotype frequencies
• by its allele frequencies

Frequency is measured by dividing the number of a particular subgroup by the total group.

Gene Pool of a Field Mouse Population described three ways:

A:

Genotype Frequencies of the mouse gene pool:

Note: The short hand f(BB) will be used to replace the long-hand "frequency of the BB genotype.”

f(BB) = 7 mice    = 0.7 or 70%

          10 mice

 f(Bb) = 1 mouse  = 0.1 or 10%

           10 mice

f(bb) = 2 mice      = 0.2 or 20%

          10 mice

B.

Phenotype frequencies of the mouse gene pool:

Note: The short hand f(Black) will be used to replace the long-hand "frequency of the black phenotype.”

f(Black) =  8 mice      = 0.8 or 80%

              10 mice

 f(White) = 1 mouse    = 0.1 or 10%

                10 mice

C.

Allele frequencies of the mouse gene pool:

Note: The short hand f(B) will be used to replace the long-hand "frequency of the B allele.”

f(B) = 15 B alleles      = 0.75 or 75%

         20 alleles

f(b) = 5 b alleles    = 0.25 or 25%

          20 alleles

(Note: there are 10 individuals, so there are 20 alleles in total.)

For Population Geneticists, the most useful way to describe a gene pool is by its allele frequencies (as in diagram C above). If you’re only given the genotype frequencies, can you still determine the allele frequencies in the gene pool? Yes!

For example, in a population of 10 mice suppose 3 are homozygous dominant, 2 are heterozygotes and 5 are homozygous recessive. What is the frequency of the dominant and recessive alleles in the population? 

Solve:

10 mice have 2 alleles each so there are a total of 20 alleles in the gene pool.

3 mice are AA, so they have 6 A alleles

2 mice are Aa, so they have 2 A alleles and 2 a alleles

5 mice are aa so they have 10 a alleles. 

Answer:   f(A)  = 8 A alleles = 0.4 or 40% of the alleles are dominant

                        20 alleles

             f(a)  =  12 a alleles = 0.6 or 60% of the alleles are recessive

                        20 alleles

Self-Check 

SC 1. Out of a population of 100 individuals, if 40% of the alleles are dominant, what is the frequency of the recessive allele in the gene pool?

SC 2. If out of a population of 20 fish, 2 are homozygous dominant, 5 are heterozygous, and 13 are homozygous recessive, what is the frequency of the recessive allele in the population?

4.8.1 page 3

Module 8: Lesson 1 Assignment—Part 1

Determining Frequencies

Retrieve your copy of Module 8: Lesson 1 Assignment that you saved to your computer earlier in this lesson. Complete Part 1. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Module 8: Lesson 1 Assignment—Part 2

Frequency Calculation

Retrieve your copy of Module 8: Lesson 1 Assignment that you saved to your computer earlier in this lesson. Complete Part 2. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Lesson 1: Part B

Get Focused

Can allele frequencies in a gene pool change?

The Amish people are the descendants of Swiss founders who immigrated to the United States in the 1800’s in an effort to renounce technological progress. One of the founders of the Amish had Ellis-Van Crevald syndrome, which causes short stature and polydactyly (extra fingers and toes). Although the allele for Ellis-Van Crevald syndrome is very rare in the Swiss gene pool, most Amish mate within their group, thus the frequency of the polydactyly allele has risen substantially in the Amish population today. 

On the other hand, some populations have allele frequencies that have stayed in relative equilibrium over time. For example, the 23 species of crocodilians have experienced great stability in their allele frequencies in the 200 million years of their existence – to the degree that not one of the 23 species has been forced into extinction in that time.

Why is it important for biologists to keep track of allele frequencies?

The definition of micro-evolution is a change in allele frequencies. If there is a relative increase or decrease in an allele, this acts as a red-flag that indicates to population geneticists that the population is experiencing some kind of pressure and is adapting in response. An increase in the frequency of the lighter coat color allele in ground squirrels versus the darker might indicate that only the lighter squirrels can remain camouflaged and survive in the dry yellow grasses that are becoming prevalent with drought conditions. This could be an indicator of the effects of global warming. 

When we say that populations are evolving (allele frequencies are changing) this is not necessarily a bad thing. Populations under pressure have two options. They can either evolve to adapt to the new conditions, or they become extinct. Clearly, evolution is the more favorable choice. 

In this lesson you will see how the Hardy Weinberg Principle is used by biologists as a toolto determine whether or not allele frequencies are changing and therefore, whether a population is evolving.

At the end of this lesson you should be able to answer the following focusing questions:

• What are the five conditions of Hardy Weinberg Equilibrium?
• What happens when conditions of HW Equilibrium are not met?

Module 8: Lesson 1 Assignment

You will complete two assignments for assessment. In Part 1 of this lesson, you dowloaded and started to complete the Module 8: Lesson 1 Assignment. You will receive further instructions on how to complete this assignment later in the lesson.

4.8.1 page 4

Explore

It would seem logical that if each breeding couple removes two alleles from the gene pool in order to reproduce, and then returns them to the gene pool in the form of offspring, that the relative frequencies of each allele in a gene pool should not change from generation to generation – in other words the population should stay in equilibrium.

Hardy Weinberg Equilibrium (HWE)

Godfrey Hardy and Wilhelm Weinberg are famous for making just that observation: That as long as certain conditions are met, allele frequencies should stay the same, generation after generation - a situation they so modestly called “Hardy Weinberg Equilibrium.”

Conditions necessary to Maintain Hardy Weinberg Equilibrium

1. The population is closed. (In other words, no immigration of individuals (and alleles!) in, or emigration out. In other words, there must be no gene flow.
2. The population is large enough that chance events (e.g. individuals who don’t mate) will not alter the frequencies. (Missing one penny out of 5 is a much bigger event statistically than missing one penny out of a thousand). No genetic drift.
3. There must be random mating. (No picking favorite phenotypes or genotypes as mates!)
4. There are no net mutations (There are always mutations, but to stay in equilibrium, the mutation rate from B to b has to equal the mutation rate from b to B.)
5. There is no natural selection. (The environment can not be favoring the survival of individuals with one allele over the other.)

So, which populations are in HWE? If you look carefully at this list, you can see it would be difficult if not impossible to think of a natural population that meets all these conditions – which is exactly the point. Hardy Weinberg Equilibrium is a hypothetical construct, and we rarely see populations in equilibrium.

If HWE is largely a hypothetical situation, then why are we interested in these 5 conditions that lead to HWE? The five conditions listed above keep populations in HWE and prevent evolution from happening. If any of the HWE conditions are not met, then the population is by definition, evolving.  

Read

To review these concepts read p. 680-82 of your textbook: Introducing the Hardy Weinberg Principle. You may wish to make summary notes, or include some example problems with their solutions in your course folder.

Watch and Listen

To review and summarize the information of this lesson, you may view the following video entitled The Hardy-Weinberg Principle: "Minding Your p's and q's.

Try This

TR 1. Identify two kinds of populations that would exhibit the five conditions of HWE. 

TR 2. Look at p. 700 of the text, question 4. Note that 11% of the Canadian population is lactose intolerant. Would this be the same in other cultures? Why or why not?

Self-Check

SC 3. A population of 20 deer was introduced to an island where no deer had previously lived. Although there were several bucks (males of breeding age), one who was much larger and stronger was able to fight off the other bucks, and was thus able to breed with the 10 or so females in the breeding population. This same scenario repeated itself for three years in a row. Is this population in Hardy Weinberg equilibrium? Why or why not?

SC 4. State a reason why the following might NOT be in Hardy Weinberg Equilibrium: 

1. Populations growing within range of radiation from the Chernobyl nuclear power plant in the Ukraine in 1986.
2. A mixed population of hooked and straight beaked birds inhabited an island. With falling sea levels, a small group of birds were able to establish a colony on a nearby island. All of those birds were straight beaked.
3. Poplar plants are typically wind pollinated. In the absence of wind during flowering, many of the ‘flowers’ are fertilized by pollen from the same flower.
4. Evening-scented stocks are flowers that give off a beautiful fragrance towards night-fall. Some flowers are more fragrant than others and attract more bees.
5. In very strong winds, poplar pollen from distant populations can be brought in and end up pollinating local plants.

Module 8: Lesson 1 Assignment

Submit your completed Module 8: Lesson 1 Assignment to your teacher for assessment.

4.8.1 page 5

Lesson Summary

When gene pool allele frequencies remain the same over time, the population is in Hardy Weinberg Equilibrium. Conditions needed for HWE are: a closed population, a large population, no net change in mutation rate, random mating, and no natural selection. If these conditions aren’t met, allele frequencies will change and by definition the population will evolve. Therefore, the conditions for evolution are: an open population (gene flow), a small population (genetic drift), change in mutation rate, non-random mating, and natural selection.

Glossary

population: organisms of a particular species in a particular place at a particular time

gene pool: a hypothetical construct consisting of all of the alleles from all of organisms of a particular population

frequency: #/total

gene flow : movement of alleles into or out of a population by immigration or emigration

micro-evolution: a change in the frequency of alleles in the gene pool

natural selection: process by which organisms with certain heritable traits survive, passing on their traits to the next generation; determined by the environmental conditions of the time 

Hardy Weinberg Principle: Allele frequencies in a population will remain the same over time as long as the population is large, there is no gene flow, there is no natural selection, there is no change in mutation rate, and there is no mate selection. If allele frequencies do change, it indicates micro-evolution is occurring in the population

Lesson 4.8.2

Lesson 2—Causes of Change in the Gene Pool

Get Focused

Why are population geneticists so concerned with allele frequencies and whether they’re increasing or decreasing? In general, the more variation there is in a gene pool the better. A population with frequencies of 99% for one allele and only 1% for another allele is in a dangerous situation. The members of the population are so alike that, if the environment were to change to favor the rare allele, there may not be enough of those alleles in the gene pool to produce enough survivors, and the population could succumb to extinction.

Domesticated animals (livestock) have been bred to become genetically very similar—producing consistent meat quality and handling traits. However, the lack of diversity in their gene pool means that they are all susceptible to the same types of disease. Similarly, animal populations that are kept isolated in wildlife reserves may suffer the same problem. They can become so similar genetically that they are all susceptible to the same environmental assaults—whether in the form of disease or climate change.

Are changes in gene pools positive or negative? What kinds of conditions produce high biodiversity and what conditions do not? In this lesson you will learn about the 5 methods by which these changes occur.

By the end of this lesson you should be able to answer to the following focusing questions:

• What are the causes of change in a gene pool?

• What factors cause changes in diversity of the composition of a gene pool?

Module 8: Lesson 2 Assignment

Complete the online assignment below

Bio30 4.8.2 online assignment

You should also watch the tutorial video for this lesson and submit a summary. 

Bio30 tut#4.8.2 changes in pop

You must decide what to do with the questions that are not marked by the teacher.

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

4.8.2 page 2

Explore

What mechanisms lead to gene pool change and micro-evolution?

If the conditions of Hardy Weinberg equilibrium are the conditions that keep allele frequencies from changing and prevent evolution, then were we to reverse the list, we would get the conditions that lead to changing allele frequencies and evolution.

The conditions that lead to micro-evolution include the following:

• An open population with gene flow in and out through immigration and emigration.
• A small population whose frequencies can be greatly affected by chance events (genetic drift).
• Mate selection – choosing mates on the basis of preferred genotypes/phenotypes.
• Changes in mutation rates – creation of either new alleles or switching from one allele to the other.
• Natural Selection – In a given environment, individuals with certain alleles are better suited for survival and reproduction than others.

These 5 mechanisms for changes in allele frequencies are therefore the tools used for species survival on an ever-changing earth.

Random copying and transcription/translation errors commonly cause dominant alleles to mutate to recessive alleles and vice versa. However, a net change in direction results in microevolution. If one begins to occur more than the other, then this net change in mutation rate will cause a change in allele frequencies and thus microevolution. This can either increase or decrease diversity in the population, depending on which is favored. The gene flow that results from immigration and emigration decreases variation between populations, but increases diversity within populations. In most species, the process of mate selection is anything but random. The complex courtship rituals, dances, and displays of animals result in sexual selection. If one phenotype/genotype is very popular with mates, the frequency of the involved alleles will increase, decreasing diversity. If the taste in mate changes, so will the allele frequencies.

The genetic drift that occurs when small populations experience major genetic change due to chance events occur where sub-populations become isolated either by migration (Founder effect) or natural disaster (Bottleneck effect). Both result in the increased frequency of a rare allele, so diversity is increased. The controlled breeding done in agriculture (crop and livestock) purposely sets up conditions of genetic drift to increase the frequency of rare but desirable alleles. Natural selection is entirely dependent on the environment of the time—those with suitable alleles survive to reproduce. If competition is fierce under conditions of rapid environmental change, the frequency of a suitable but rare allele will increase, giving its owner a survival advantage, increasing diversity in the gene pool. If there are no variants in the population with suitable alleles, extinction occurs.

Read

Read p. 689-695 of your text to understand these processes. You may wish to make summary notes, or a chart of the ideas presented.

Self-Check

Compare and contrast.

Complete the following and file in your course folder for study purposes.

Compare and contrast the following terms:

1. The founder effect and the bottleneck effect (as causes of genetic drift)
2. Natural selection and genetic drift
3. Non-random mating and natural selection

Self-Check

1. Question 19 on page 695. Provide an example.

2. Impediments to gene flow are often geographical barriers. Provide 3.

3. The bottleneck effect can occur after a natural disaster. Give 3 examples of a natural disaster that could result in this type of genetic drift.

4. The Launch Lab on page 676-7 allows you to select mate phenotypes/genotypes of sage grouse during their mating displays, and see the results. Pick out 3 characteristics that the female may be using to select the best mate.

5. How can wildlife preserves prevent the negative effects of genetic drift and lost biodiversity in wildlife populations.

4.8.2 page 3

Module 8: Lesson 2 Assignment

Retrieve your copy of Module 8: Lesson 2 Assignment that you saved to your computer earlier in this lesson. Complete the assignment. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Discuss

With the guidance of your instructor, and working with fellow students, prepare the following discussion material for debate.) Half of the class should take the part of ranchers and the public in the surrounding area; the other half should take the part of wildlife managers. Prepare your position and discuss your findings with fellow students on the discussion board.

Debate the advantages and disadvantages of introducing the grey wolf back into Montana’s Glacier National Park. (Refer to Fig 19.10 on page 691 for more background information.)

Self-Check

1. Which gene pool would most likely demonstrate micro-evolution?
   
   
   1. A gene pool in Hardy Weinberg equilibrium
   2. A gene pool bearing a new mutation
   3. A large gene pool
2. Which correctly matches a term to its description?
   
   
   1. gene flow – a chance change in allele frequencies when small populations become isolated
   2. natural selection – a particular phenotype of mate is more often chosen
   3. change in mutation rate – several new mutations arise in a short period of time
   4. genetic drift – unrepresentative populations are separated from a larger population

Lesson Summary

The five causes of changes in frequency of alleles in the gene pool (micro-evolution) are:

1. Genetic drift – changes due to small populations. Typically decreases diversity. Examples are Founder and Bottleneck effects
2. Natural selection – Organisms with certain phenotypes/genotypes have selective advantage over others. This typically decreases diversity, especially in very competitive environments. Heterozygotes typically have the same advantage as the homozygous dominant genotype unless there is a heterozygote advantage
3. Change in mutation rates – a greater rate of mutation from one allele to the other – increases the frequency of one allele over the other. Typically decreases diversity. Mutations resulting in new alleles increase diversity
4. Non-random mating – choosing one allele over another in preferred mates is known as sexual selection and increases the frequency of one allele over the other, typically decreasing diversity
5. Gene flow - immigration and emigration increases diversity within populations, but decreases diversity between populations

Submit your completed Module 8: Lesson 2 Assignment to your teacher for assessment.

Lesson 4.8.3

Lesson 3—Hardy Weinberg Calculations

Get Focused

You may have heard of cystic fibrosis, which is a disease where the body produces abnormally thick, sticky mucus in the lungs and digestive system. Victims have chronic difficulty breathing, respiratory infections, and poor weight gain. CF is an autosomal recessive condition that occurs in 1 in 2500 Caucasian births. In the past, victims often did not live long enough to reproduce. With intensive therapy and medication, those with CF are now living long enough to have children and pass on the CF allele. Population geneticists are interested in what this means for the frequency of the CF allele in future populations.

Two scientists Wilhelm Hardy and Godfrey Weinberg, in addition to giving us the conditions for HW Equilibrium and the conditions for evolution, have also given us an equation that allows us to figure out allele frequencies and genotype frequencies quite easily. You will see how biologists can use this information to determine if populations are changing (adapting and evolving), and if so, help determine what factors are causing the changes.

.

By the end of this lesson you should be able to answer the following focusing questions:

• How can the Hardy Weinberg formula, graphs, and data be used to study changes in populations over time?
• How do we analyze and interpret data, to make predictions and decisions about population management?

Module 8: Lesson 3 Assignment

  Once you have completed all of the learning activities in the lesson, you can complete the online assignment.

Bio30 4.8.3 online assignment

You should also watch the tutorial video for this lesson and submit a summary.  Bio30 tut# 4.8.3 hardy weinburg

In addition to your lesson work as listed below, any summary notes, sample calculations, diagrams, charts or tables should be stored in the course folder for your teacher’s feedback and study as you prepare for exams.

You must decide what to do with the questions that are not marked by the teacher. Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

4.8.3 page 2

Explore

In addition to giving us the conditions for genetic equilibrium and micro-evolution, Hardy and Weinberg also gave us a mathematical formula that allows us to go back and forth between determining allele frequencies and genotype frequencies. The symbols used are p and q. (For these examples we’ll use A as the dominant allele and a as the recessive allele.)

p = frequency of the dominant allele = f(A) =     the # of the dominant alleles         
                                                              the total # of alleles in the population
           
q = frequency of the recessive allele = f(a) =     the # of the recessive allele          
                                                              the total # of alleles in the population

If(A) + f(a)  =  all the alleles in the population, so:

p     +   q     =   1

Follow the logic on the Punnett square on p. 682 and you will see how Hardy and Weinberg derived the following equation for determining the frequency of each genotype in the population. (For this example in the Punnett square, their assumption is that 0.70 or 70% of the alleles in the gene pool are dominant: f(B) = 0.70, and that 0.30 or 30% of the alleles in the gene pool are recessive:
f(b) = 0.30 or 30%)

The Hardy Weinberg equation we use to predict the frequency of genotypes in a population is:

 p2      +       2pq      +      q2      =     1
f(BB)   +     f(Bb)     +     f(bb)    =    the whole population 

where:            

p2 = the frequency of the homozygous genotype in the population

 p2 = f(AA)

2pq = the frequency of the heterozygous genotype in the population

2pq = f(Aa)

q2 = the frequency of the homozygous recessive genotype in the population
 q2 = f(aa)

Read 

Read carefully through the sample problems on p. 682-3 and work them out yourself using pen and paper. You will need a calculator.

Here is another sample problem if you need a little more help:

Assume that in grizzly bear populations, brown-tipped fur is dominant to silver-tipped fur.

For the purposes of this problem assume A indicates the brown tipped allele, and a indicates the silver–tip allele.

For each question, first of all, decide which of the following you’ve been given in the question. Then decide which of the following you want to find.

p                   q                     p2                  2pq                  q2
f(A)               f(a)                  f(AA)               f(Aa)               f(aa)

1. If 45 of 75 grizzly bears have the recessive phenotype of silver-tipped fur, what is the frequency of the recessive allele in this population of grizzlies?
   
   
   • Given: 45/75 or 0.6 of the bears have the recessive phenotype, and therefore the genotype of aa. The frequency of aa is q2, so you’re given: q2 = 0.6
   • Want: The frequency of the recessive allele, so you want: q
     
     
   • Solve: square root  q2 to get q = 0.774
     
     Answer: 0.77 or 77% of the alleles in the gene pool are recessive.
     Note; remember to read the questions carefully, especially on exams. Does the question require frequency, or % frequency?
2. What percentage of the population of bears are heterozygotes?
   
   
   • Given: 45/75 or 0.6 of the bears have the recessive phenotype, and therefore the genotype of aa. So, you’re given: q2 = 0.6
   • Want: the percentage of bears of the heterozygous genotype (Aa) in the population, so you want: 2pq
   • Solve: Square root q2 to get q.  q = 0.77
               p + q = 1, so 1 - q = p.   p = 0.23
               2pq = 2 (0.23) (0.77)   2pq = 0.35
     
     Answer: 35% of the bears in this population are heterozygotes.
3. How many bears are pure-breeding for the brown-tipped phenotype?
   
   
   • Given: 45/75 or 0.6 of the bears have the recessive phenotype, and therefore the genotype of aa. So, you’re given: q2 = 0.6
   • Want: Number of bears pure-breeding for the brown-tipped phenotype or the AA genotype, so you want: p2
     
     
   • Solve:
              The square root of q2 gives you q.    q = 0.77
               p + q = 1, so 1 - q = p                   p = 0.23
               p2 = f(AA) = 0.05
     
     Answer: 0.05 or 5% of the 75 bears are pure-breeding for brown-tipped hair. Therefore 6 of the 75 bears are pure–breeding brown tipped hair.
4. If 10 years ago, only 24 of 77 bears had silver-tipped fur, has evolution occurred? Justify your answer.
   
   By definition, evolution has occurred if the allele frequencies have changed, so we have to find p or q for these two dates and compare them.
   
   Solve:
   • Bears with silver-tipped fur are those with aa genotype or q2
   • q2 10 years ago = 24/77 = 0.31      Now q2 = 45/75 = 0.6
   • q ten years ago = 0.096                Now q is 0.36
     
     Answer: Yes, evolution has occurred because the allele frequencies have changed.

Here is a question that goes the other direction, from genotype frequency to allele frequency. It uses a fictitious organism called dworps. Dworps can be tall (dominant) or short (recessive). If 50% of dworps are tall, what’s the frequency of the tall allele in the gene pool? (A = tall, a = short)

• Given: 0.5 are tall = f(AA) + f(Aa)
• So, 0.5 are short = f(aa), which is q2
• Want: p = f(A), and you have q2.
• Solve: square root of q2 = q = 0.71, So p = 1 - q= 0.29
  
  Answer: the frequency of the dominant allele (p) = 0.29

4.8.3 page 3

Read

Read pages 681-p.685 of your text to review these concepts and calculations. It can be challenging, but practicing problem solving will ensure your mastery of this material. Answer questions in your text and discuss your work with your instructor if you need assistance.

Watch and Listen

• View Biologix video The Hardy-Weinberg Principle: "Minding Your p's and q's.

Try This

Turn to page 688, #8. Graph the frequency of the dominant allele using the same graph.

 
Answer: Remember, p = f(A) and q = f(a), so p + q = 1. Therefore, the graph for the frequency of the recessive allele will be plotted as the exact opposite. If p = 0.4, q must be 0.6. Where p = 0.85, q must be 0.15, etc.

Remember that your success in this concept depends on your ability to successfully solve problems. Practice is essential to mastery.

Self-Check

Do #4 pf the "Practice Problems" on page 683 of your text. Your answers should be:

4.8.3 page 4

Reflect and Connect

In this lesson you have learned how to calculate changing frequencies of alleles. These changes can illustrate that a population is evolving. These changes can be in response to a changing environment. For example, the increase in the allele for light brown hair in many species of gopher is increasing as these individuals survive in a habitat that is becoming increasingly arid.

Why do ecologists study population changes? By using past studies what can they predict. Scientists are learning about the affects of climatic changes on species and their characteristics. They can use these studies to explain changes in populations due to weather conditions, disease, change in prey-predator relationships, and many other factors that you have read about in your text. Humans are realizing the effect of our practices on the environment and the impact to other species and their populations. By understanding the causes of allele frequency changes, we may better understand the impact that man has on the ecosystem.

Lesson Summary

• The Hardy Weinberg equation is a tool used to determine if genetic change (evolution) is actually occurring in a population.
   
• In terms of the allele frequencies, p represents the frequency (#/total) of the dominant allele in the gene pool. q represents the frequency of the recessive allele in the gene pool. p + q = 1 because the dominant alleles plus the recessive alleles make up the whole gene pool.
• p2 represents the frequency of the homozygous dominant genotype in the population = f(AA)
• 2pq represents the frequency of the heterozygous genotype = f(Aa)
• q2 represents the frequency of the homozygous recessive genotype = f(aa)
• p2 + 2pq + q2 = 1 because f(AA) + f(Aa) + f(aa) = all individuals of the population.

Lesson 4.8.4

Lesson 4—Human Activity, Biotechnology, and Gene Pools

Get Focused

Humans are the only species on Earth that have the ability to change their environment significantly. A very large brain and a wonderfully dexterous opposable thumb are a winning combination that has allowed us to develop technologies to meet our need for food, shelter, and safety. Too often this has been at the expense of other species we share our habitats with, often with unintended consequences.

However, technology has also provided the means by which we can manage and preserve both wild and domestic populations more effectively and with more positive outcomes.

By the end of this lesson you should be able to answer the following focusing question:

• What are the intended and unintended consequences of human scientific and technological developments on gene pools?

Module 8: Lesson 4 Assignment

There is no assignment for this lesson but you are responsible to know this information for the unit exam.

Any summary notes should be stored in the course folder for study as you prepare for exams. 

You must decide what to do with the questions that are not marked by the teacher.

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

4.8.4 page 2

Explore

As humans, with all our technologies, we have had a significant impact on other populations in our ecosystem. Many of man’s practices are controversial. For example:

• Not many people would think of bacteria or viruses as natural populations, but they certainly qualify. Antibiotics used to destroy bacteria can give a selective advantage to those bacteria that have alleles for antibiotic resistance. Many commonly used antibiotics are no longer effective because of this rapid evolution in many bacterial species. What does this mean for our ability to control disease in the future?
• Biotechnology, the use of organisms to benefit humanity, can be as simple and low-tech as selective-breeding programs to produce bigger crop yields or to produce livestock with more meat and better handling characteristics. Newer biotechnologies go beyond basic agriculture, inserting desirable genes from one species into another, producing transgenic organisms that are more profitable. Ethical questions arise when we ask whether transgenic organisms are new species and whether genetic engineers are altering the course of evolution. If so, is it justifiable?
• The unintended effects of introducing genes into organisms include effects on non-target genes and ‘jumping’ of genes from one species to another.  Is there adequate regulation and research to safeguard the gene pools of these species? On the other hand, is it possible to feed a hungry planet without the use of these biotechnologies?
• Cloning has been used in an attempt to save endangered species from extinction, thus preserving gene pools. Similarly, animals with inserted genes (e.g. for interferon, an anti-cancer drug) are being cloned and used as pharmaceutical factories. The cloned animals produce milk from which these expensive drugs are extracted. Are these reasonable uses of science and technology that justify manipulating gene pools?
• The introduction of exotic species often results in unintended consequences to gene pools. For example:
  
  
  • Wild boars have recently been proclaimed ‘pests’ in central Alberta. The Boars were brought from Europe to satisfy a growing market for boar meat. The animals are being raised as domestic livestock. However, traditional fencing is no match for wild boars and they have escaped from boar farms in large numbers, digging up cropland in search of roots and menacing people. They have few predators because of their size (and tusks!), and they breed in the wild at an alarming rate.
• Gene banks preserve the DNA sequences of genes from organisms that are endangered or extinct. 

Read

To further understand the impact of human activity, read p. 695-6 in your text.

Self-Check

SC 1. Maintaining Genetic diversity in Whooping Cranes p. 696.  Complete questions 1- 3.

Try This

Livestock Genetics

TR 1. Is it desirable to farmers that livestock populations remain in Hardy Weinberg Equilibrium?

TR 2. Are small, genetically similar populations of livestock subject to the negative effects of inbreeding and genetic drift? Why or why not?

Self-Check

Gene banks store the DNA sequences of genes from organisms that are endangered or extinct. Of the hundreds of varieties of rice that used to be grown, only a very few are grown now. The same can be said of potatoes (only the varieties used to make French fries are profitable now). Why store these gene sequences? What possible use could they be in the future?

Read p 695: Human activities and genetic diversity in order to answer the following:

SC 2. List 4 human activities that have had consequences for gene pools of natural populations. State how each has affected genetic diversity in a target population. State whether the effect was intended or unintended.

4.8.4 page 3

Lesson Summary

Technologies developed to meet human needs often have consequences for gene pools of natural populations – some intended, some not.

Intended:

• Use of antibiotics increase natural selection and frequency of resistant alleles in bacterial populations. 
• Widespread and effective medical/pharmaceutical/surgical technologies increase survivability of individuals with deleterious alleles.
• Transfer of advantageous genes into crops and livestock improve yields and profitability, but change gene pools and evolutionary paths.
• Cloning of endangered or possibly extinct organisms is done to preserve rare alleles. 
• Crops and livestock with advantageous qualities are cloned to create a uniform and economically profitable product, but this reduces diversity in the gene pool. 
• Creation of wild-life corridors increases gene flow and maintains diversity in populations.
• Creation of wildlife preserves can lead to genetic drift if either the Founder or the Bottleneck effect is in play. Wildlife preserves lead to inbreeding which can also result in genetic drift reducing diversity substantially.

 Unintended:

• Agriculture, dam construction, road building, urban sprawl, logging, and industrialization result in habitat destruction and fragmentation leading to rapid selection and reduced genetic diversity.
• Over-hunting can reduce diversity by removing ‘desirable’ alleles from the gene pool. (e.g. the biggest and strongest animals are valued more by hunters)
• Introducing genes into crops and livestock can have unintended effects on the expression of other genes, leading to reduced survivability and loss of diversity.
• Genes introduced into domestic species can ‘jump’ to wild species, changing the gene pool substantially. (e.g. gene for herbicide resistance jumping from corn to weed species)

4.8.4 page 4

Reflect and Connect

When taking antibiotics it is advised that you take the drug at regular time intervals. Can you think of why it is important to take the drug at the times specified?

In order for a drug to have its desired effect it has to reach a certain concentration in the body. This concentration can be regarded as an equilibrium concentration since it is a result of the processes of ingestion and adsorption (that will increase the concentration) of the drug, and the processes of metabolism and excretion (that will reduce drug concentration). Can you think of how the processes to reach an equilibrium in the concentration of a medicine in the body are similar to the investigation you performed in this lesson where you simulated a dynamic equilibrium?

Lesson Summary

In this lesson you investigated the following essential question:

• What procedures are used to calculate the chemical quantities for all substances in a chemical system?

You applied your skills in performing stoichiometric calculations to analyze chemical systems in equilibrium. You found that constructing an ICE table is a convenient way to identify the relevant calculations that must be performed to complete this type of analysis.

In Lesson 5 you will learn more about how an equilibrium system can be analyzed using quantitative techniques.

Module Summary

 Genetic variation is ammunition against extinction. As environmental conditions change, genetic variation increases the probability that at least some individuals will survive in the new environment and carry on the species. The new skills you have learned will allow you to determine allele and genotype frequencies in a population, and predict whether a population is evolving or is in equilibrium.  Having discovered the mechanisms of genetic change (evolution), you can now infer from case histories whether a population is susceptible to change and what factors have led to it. Human activity is notorious for causing habitat change and disruption in natural populations, both as a result of intended actions and unintended actions. Your studies have allowed you to discover how our actions impinge on gene pools and genetic diversity. You should now have a better understanding of our role in causing genetic change, and what we can do to reduce our impact on natural populations.

Module Assessment

You should have submitted tutorial summaries for all tutorial videos in this modules as well as submitted the assignments listed below.

Bio30 4.8.1 online assignment

Bio30 4.8.2 online assignment

Bio30 4.8.3 online assignment