Transcript Biol 178 Lecture 31

Bio 178 Lecture 31
Mutation and Evolution of Populations
 J. Elson-Riggins
Reading
•
Chapters 20 (P 410-411) & 21
Quiz Material
•
Questions on P 432 & 452
•
Chapters 20 & 21 Quizzes on Text Website
(www.mhhe.com/raven7)
Mutation
Changes in the hereditary message of an organism.
• Somatic Mutations
Not inherited, but can have a profound effect on the
individual, eg. Cancer.
• Germ-Line Mutations
Inherited.
Importance
Starting point for evolution - mutation produces new
alleles and recombination shuffles them.
Do all Germ Line Mutations Increase Genetic Fitness?
No - May reduce, maintain, or increase progeny number.
Types of Mutation
• Insertion
• Deletion
• Base Substitution
Changes in Gene Position (Recombination)
• Chromosomal Rearrangement
• Insertional Inactivation
Types of Mutation
Question Example
1 (a) What are the consequences of changing the sixth base of the
following DNA sequence to a “C”? 3-TACAATGGTATT-5 
(b)
What are the consequences of deleting the sixth base?
AAAS Position on Science and Religion
• Please consult the following website for information
regarding this subject and guidelines for teaching science
in schools. This site states the opinions of scientists and
religious clergy. The website includes a downloadable
guide for teachers.
http://www.aaas.org/programs/centers/pe/evoline/index.shtml
Evolution and Natural Selection
• Evolution
Change in species over time (descent with modification).
• Natural Selection
The process by which individuals (with characteristics that
are advantageous in a particular environment) produce
more offspring than other individuals.
Over time, the population will become better adapted to
the environment.
• Opposing Theories for Evolutionary Mechanism
Lamarck - Variation is acquired during the lifespan of the
organism and passed on to the offspring.
Evolutionary Theories
Changing Allele Frequencies in Populations
• Polymorphism
When a gene in a population has more than one allele
present at frequencies greater than would occur by newly
arising mutations alone.
Can be studied at the DNA level by sequencing the DNA of
population members.
• Allele Frequencies
The proportion of each allele type in a population.
• The Hardy-Weinberg Principle
1908 - Hardy and Weinberg determined why genetic
variation persists in populations.
The Hardy Weinberg Principle (Cntd.)
• Hardy-Weinberg Equilibrium
When the allele frequencies do not change through the
generations - zero evolution.
Will occur if:
1. No mutation.
2. No selection.
3. No immigration.
4. Mating is random.
5. Population size is large.
The Hardy Weinberg Principle (Cntd.)
• Calculating Allele Frequencies
*Allele frequencies will not change if a population is in HardyWeinberg equilibrium.
Equation
p2 + 2pq + q2 = 1
Where p = frequency of most common allele.
q = frequency of less common allele.
Example 1
A population of 200 cats is composed of 168 black
individuals & 32 white individuals. Black (B) color is
completely dominant to white (b) color.
What proportion of the population would be expected to
be (i) heterozygous (ii) homozygous dominant?
The Hardy Weinberg Principle (Cntd.)
Example 2
In a population of red (dominant) and white flowers,
the frequency of red flowers is 91%. What is:
(a) The frequency of the red allele?
(b) The frequency of homozygous dominant individuals?
(c) The frequency of heterozygous individuals.
Agents of Evolutionary Change
Changing Allele Frequencies
Allele frequencies in a population can be altered by:
• Mutation
The ultimate source of genetic variation.
Random.
But…occurs at a very low rate  is not an important
factor in the evolution of populations - the other factors
have a greater effect.
• Gene Flow (Migration)
Movement of alleles from one population to another.
Maintenance of new allele frequencies are dependent on
whether the migrating individual(s) can adapt to the new
environment.
Changing Allele Frequencies (Cntd.)
• Nonrandom Mating
1. Assortative Mating
When phenotypically similar individuals mate.
Increases the proportions of homozygotes.
2. Disassortative Mating
When phenotypically different individuals mate.
Increases the proportions of heterozygotes.
Changing Allele Frequencies (Cntd.)
• Genetic Drift
Random change in allele frequencies of a population as a
result of chance events.
Founder Effects
One or a few individuals leave a population and establish a
new one.
The alleles of these founders will be very significant in the
new population, even if they were rare in the original
population.
Eg. Galápagos Islands.