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Evolution & Microevoluti on Tutorial Introduction Microevolution Hardy Weinberg Equilib rium Practice!

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Page 1: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Evolution & Microevolution TutorialIntroductionMicroevolutionHardy Weinberg EquilibriumPractice!

Page 2: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

In this tutorial, you will learn:

The difference between macroevolution & microevolution.

How Hardy-Weinberg equilibrium works as well as factors that can upset this equilibrium.

How to use the equation, p2 + 2pq + q2 = 1, to calculate allele frequencies in a population.

Credits:Figures and images by N. Wheat unless otherwise noted.Lesser ball python image used with permission from Tim Bailey, Bailey & Bailey Reptiles.Funded by Title V-STEM grant P031S090007.

Page 3: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Introduction

Evolution – includes all of the changes in the characteristics and diversity of life that occur throughout time. Evolution can occur on both large and

small scales.

Page 4: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Macroevolution – Evolution on a Large Scale

Macroevolution – evolutionary change on a grand scale. Origin of novel designs Evolutionary trends Adaptive radiation

Page 5: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Microevolution – Evolution on a Small Scale

Microevolution - a change in the genetic composition of a population over time. A change in the frequency of certain

alleles in a population over several generations.

Page 6: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Polymorphism

Polymorphism occurs when there are different allelic forms of a gene in a population. Mojave (left) and Lesser (middle) are

different alleles of the same gene. Wild type ball python is shown on the right.

Photo courtesy of Bailey & Bailey Reptiles

Page 7: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Gene Pool

All of the alleles of all of the genes possessed by all of the members of the population are contained in the gene pool of the population.

We can measure the relative frequency of a particular allele in a population. Allelic frequency

Page 8: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Population Genetics

Population Genetics – the study of how populations change over time. Dependent on both Darwin’s theory of

natural selection and Mendel’s laws of inheritance.

All heritable traits have a genetic basis, some are controlled by multiple genes – not as simple as in Mendel’s studies.

Page 9: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Genetic Equilibrium

According to Hardy-Weinberg equilibrium, the hereditary process alone does not produce evolutionary change. Allelic frequency will remain constant

generation to generation unless disturbed by mutation, natural selection, migration, nonrandom mating, or genetic drift. These are sources of microevolutionary

change.

Page 10: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Frequency of Alleles

Each allele has a frequency (proportion) in the population.

Example population of 500 wildflowers. CRCR = red; CRCW = pink; CWCW = white

250 red, 100 pink, 200 white Frequency of CR = (250 x 2) + 100 / 1000 = 600/1000 =.6 =

60%

Page 11: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Frequency of Alleles

p is the frequency of the most common allele (CR in this case). p = 0.6 or 60%

q is the frequency of the less common allele (CW in this case).

p + q = 1 q = 1- p = 1 – 0.6 = 0.4 or 40%

Page 12: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem

Populations that are not evolving are said to be in Hardy-Weinberg equilibrium.

Page 13: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem As long as Mendel’s laws are at work,

the frequency of alleles will remain unchanged.

Review Punnett squares in the genetics tutorial.

Page 14: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem

The Hardy-Weinberg theorem assumes random mating.

Generation after generation allele frequencies are the same.

Page 15: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem

Conditions required for Hardy-Weinberg equilibrium to hold true: Very large population No gene flow into or out of the population No mutations Random mating No natural selection

Page 16: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem

Departure from these conditions results in a change in allele frequencies in the population.Evolution has occurred!

Page 17: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

Frequency – the proportion of individuals in a category in relation to the total number of individuals.

100 cats, 75 black, 25 white – frequency of black = 75/100 = 0.75, white =0.25. Two alleles: p is common, q is less

common. p+q = 1

Page 18: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

The frequency of black cats is:

0.75 75 0.25 25 100

Question 1

Page 19: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 1

Page 20: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 1

Page 21: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

What would the frequency of black cats be if the population size

was 80 instead of 100 (still 75 black)?

0.75 75 0.94 (75/80) 1

Question 2

Page 22: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 2

Page 23: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 2

Page 24: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Hardy-Weinberg Theorem

At a locus with two alleles, the three genotypes will appear in the following proportions:

(p + q) x (p + q) = p2 + 2pq + q2 = 1

Page 25: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

(p + q)2 = p2 + 2pq + q2

Individuals homozygous for allele B

Individuals heterozygous for alleles B & b

Individuals homozygous for allele b

Page 26: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

We will use a population of 100 cats as a practice example. 84 of the 100 cats are black. 16 are white.

Page 27: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

We can use the equation and our color observations to calculate allele frequencies in our population of 100 cats. p2 + 2pq + q2 = 1 100 = population size

Page 28: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

84 of our 100 cats are black. Black is the dominant phenotype.

Cats with the genotype Bb or BB will be black.

The frequency of black cats is 84/100, but we can’t yet say anything about the B allele.

See the genetics tutorial to review these terms.

Page 29: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

16 of our 100 cats are white. White is recessive (bb) and is

represented by q2 in our equation: p2 + 2pq + q2 = 1

So, q2 = 16/100 = 0.16 q = square root of 0.16 = 0.40.

Page 30: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

q = square root of 0.16 = 0.40. Since p + q = 1; p = 1 – q = 0.60. p2 = 0.36

p2 represents the proportion of individuals in the population with the homozygous dominant phenotype (BB).

Remember population size = 100

Page 31: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

So, the number of cats in our population that have the BB

genotype would be: 0.36 cats 0.36 x 100 = 36 cats 0.16 x 100 =16 cats 84 cats

Question 3

Page 32: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 3

Page 33: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 3

Page 34: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Practice with Hardy Weinberg

Now we know how many of our cats have the BB genotype and the bb genotype.

We can find the number of Bb cats using our equation: p2 + 2pq + q2 = 1.

2pq represents the proportion of cats with Bb. 2 x 0.6(p) x 0.4(q) = 0.48 0.48 x 100 = 48 cats with Bb genotype.

Page 35: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Let’s try another! In our population of 100 cats, 75 are black & 25 are white.

Where do we start? 75 black cats = p2.

75/100 = 0.75 black cats = p2.

25 white cats = q2.

25/100 = 0.25 white cats = q2.

Need more information.

Question 4

Page 36: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 4

Page 37: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 4

Page 38: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

If q2 = 0.25, q=

0.05 5 0.5 50

Question 5

Page 39: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 5

Page 40: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 5

Page 41: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

If q=0.5, p=

0.5 5 0.6 0.1

Question 6

Page 42: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 6

Page 43: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 6

Page 44: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

So, if p=0.5, and p2=0.25, how many of our cats have

the BB genotype? 0.25 25 50 75

Question 7

Page 45: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

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Question 7

Page 46: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 7

Page 47: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Now, how many of the cats are heterozygous (Bb)?

48 100 .5 50

Question 8

Page 48: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Sorry! That is incorrect. Try again!

Question 8

Page 49: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 8

Page 50: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

If we measure allele frequency one year at p=0.8 & q=0.2 and then go back 5

generations later to find p=0.5 & q=0.5, what has happened?

The population has remained in Hardy-Weinberg equilibrium.

The population has doubled in size.

There has been a change in allele frequencies: evolution has occurred.

Nothing has changed.

Question 9

Page 51: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

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Question 9

Page 52: Evolution & Microevolution Tutorial Introduction Microevolution Hardy Weinberg Equilibrium Practice!

Congratulations! You are correct!

Question 9