Title: Evolution & Microevolution Tutorial
1Evolution Microevolution Tutorial
- Introduction
- Microevolution
- Hardy Weinberg Equilibrium
- Practice!
2In 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.
3Introduction
- 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.
4Macroevolution Evolution on a Large Scale
- Macroevolution evolutionary change on a grand
scale. - Origin of novel designs
- Evolutionary trends
- Adaptive radiation
-
5Microevolution 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.
6Polymorphism
- 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
7Gene 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
8Population Genetics
- Population Genetics the study of how
populations change over time. - Dependent on both Darwins theory of natural
selection and Mendels laws of inheritance. - All heritable traits have a genetic basis, some
are controlled by multiple genes not as simple
as in Mendels studies.
9Genetic 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.
10Frequency 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
11Frequency 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
12Hardy-Weinberg Theorem
- Populations that are not evolving are said to be
in Hardy-Weinberg equilibrium.
13Hardy-Weinberg Theorem
- As long as Mendels laws are at work, the
frequency of alleles will remain unchanged.
Review Punnett squares in the genetics tutorial.
14Hardy-Weinberg Theorem
- The Hardy-Weinberg theorem assumes random mating.
- Generation after generation allele frequencies
are the same.
15Hardy-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
16Hardy-Weinberg Theorem
- Departure from these conditions results in a
change in allele frequencies in the population. - Evolution has occurred!
17Practice 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.
- pq 1
18The frequency of black cats is
Question 1
19Sorry!
Question 1
- That is incorrect.
- Try again!
20Congratulations!
Question 1
21What would the frequency of black cats be if the
population size was 80 instead of 100 (still 75
black)?
Question 2
22Sorry!
Question 2
- That is incorrect.
- Try again!
23Congratulations!
Question 2
24Hardy-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
25Practice with Hardy Weinberg
Individuals homozygous for allele B
Individuals heterozygous for alleles B b
Individuals homozygous for allele b
26Practice 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.
27Practice 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
28Practice 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
cant yet say anything about the B allele. - See the genetics tutorial to review these terms.
29Practice 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.
30Practice 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
31So, the number of cats in our population that
have the BB genotype would be
Question 3
- 0.36 cats
- 0.36 x 100 36 cats
- 0.16 x 100 16 cats
- 84 cats
32Sorry!
Question 3
- That is incorrect.
- Try again!
33Congratulations!
Question 3
34Practice 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.
35Lets try another! In our population of 100 cats,
75 are black 25 are white. Where do we start?
Question 4
- 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.
36Sorry!
Question 4
- That is incorrect.
- Try again!
37Congratulations!
Question 4
38If q2 0.25, q
Question 5
39Sorry!
Question 5
- That is incorrect.
- Try again!
40Congratulations!
Question 5
41If q0.5, p
Question 6
42Sorry!
Question 6
- That is incorrect.
- Try again!
43Congratulations!
Question 6
44So, if p0.5, and p20.25, how many of our cats
have the BB genotype?
Question 7
45Sorry!
Question 7
- That is incorrect.
- Try again!
46Congratulations!
Question 7
47Now, how many of the cats are heterozygous (Bb)?
Question 8
48Sorry!
Question 8
- That is incorrect.
- Try again!
49Congratulations!
Question 8
50If we measure allele frequency one year at p0.8
q0.2 and then go back 5 generations later to
find p0.5 q0.5, what has happened?
Question 9
- 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.
51Sorry!
Question 9
- That is incorrect.
- Try again!
52Congratulations!
Question 9