Bio 178 Lecture 31Mutation 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)

MutationChanges in the hereditary message of an organism.

• Somatic MutationsNot inherited, but can have a profound effect on the individual, eg. Cancer.

• Germ-Line MutationsInherited.

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 Example1 (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• EvolutionChange in species over time (descent with modification).

• Natural SelectionThe 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 MechanismLamarck - Variation is acquired during the lifespan of the organism and passed on to the offspring.

Evolutionary Theories

Changing Allele Frequencies in Populations• PolymorphismWhen 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.

• The Hardy-Weinberg Principle1908 - Hardy and Weinberg determined why genetic variation persists in populations.

• Allele Frequencies

The proportion of each allele type in a population.

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 Hardy-Weinberg equilibrium.Equation

p2 + 2pq + q2 = 1Where p = frequency of most common allele.

q = frequency of less common allele.

Example 1A 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 FrequenciesAllele frequencies in a population can be altered by:

• MutationThe ultimate source of genetic variation.

But…occurs at a very low rate is not an important factor in the evolution of populations - the other factors have a greater effect.

Random.

• 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.