Chapter 16 – The Evolution of Populations and Speciation

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# Chapter 16 – The Evolution of Populations and Speciation - PowerPoint PPT Presentation

Chapter 16 – The Evolution of Populations and Speciation. Genetic Equilibrium. Population genetics – study of evolution from a genetic point of view. Evolution – gradual change in the genetic material of a population. A population is the smallest unit in which evolution occurs. Variation.

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### Chapter 16 – The Evolution of Populations and Speciation

Genetic Equilibrium
• Population genetics – study of evolution from a genetic point of view.
• Evolution – gradual change in the genetic material of a population.
• A population is the smallest unit in which evolution occurs.
Variation
• Measuring frequency of a variation.
• Most of the time the differences are shaped like a bell curve.
• Most organisms have an average characteristic.
• Ex. Length of fish
Causes of Variation
• Mutation
• Recombination
• Random fusion of gametes
Allele Frequencies and the Gene Pool
• Gene pool – total genetic information available in a population.
• All the genes in a population that can be expressed in future generations.
• Ex. Two forms of allele A and a in a set of 10 gametes. If half the gametes carry the allele A, we can say that the allele frequency of A is 0.5 or 50%.
Allele Frequency
• Determined by dividing the number of a certain allele by the total number of alleles of all types in the population.
• Certain allele = five A allele
• Total number of alleles = ten gametes
Class Allele Frequency
• Brown hair allele frequency
• Number of people carrying an allele for brown hair = __________
• Total number of alleles = ________

Is this an accurate calculation?

Predicting Phenotype
• Phenotype frequency – the number of individuals with a particular phenotype divided by the total number of individuals in the population.
• Ex. Four o’clock flowers; 4 pink plants out of 8 plants. 0.5 pink
• Pg. 301
Genotype Frequencies
• Frequency of certain genotypes.

ex.

Frequency of RR

*remember Law of Probability

Frequency of R x Frequency of R = Frequency of RR pair

0.75 x 0.75 = 0.5625 (RR)

Frequency of r x Frequency of r = Frequency of rr pair

0.25 x 0.25 = 0.0625 (rr)

The frequencies of all types must add up to 1.0.

1.0 – frequency of RR – frequency of rr = frequency of Rr

1.0 – 0.5625 – 0.0625 = 0.375 (Rr)

Hardy-Weinberg Genetic Equilibrium

Wilhelm Weinberg and Godfrey Hardy showed that allele frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences.

Hardy-Weinberg genetic equilibrium

Requirements for this to be true:
• No net mutations occur; allele frequencies do not change overall because of mutation
• Individuals neither enter nor leave the population
• The population is large
• Individuals mate randomly
• Selection does not occur
Theory
• This is theoretical.
• Hardy and Weinberg allowed us to see what disrupts equilibrium.
H.W.
• Pg. 302
• Questions 1-6
Ch. 16: sec. 2 – Nonrandom Mating
• Many species do not mate randomly.
• Most mate by geographic proximity.
• This might lead to organisms mating with closely related organisms.
• Increasing homozygous recessive genotypes. --- disorders
Assortative Mating
• Selecting mates with similar characteristics.
Natural Selection
• The 5th requirement for Genetic Equilibrium.
Stabilizing Selection
• Individuals with the average form of a trait have the highest fitness.
• Extreme forms are selected against.
• Allele frequencies stay the same.
Directional Selection
• Individuals with a more extreme form of a trait are selected for.
• Allele frequencies are going in a direction.
Disruptive Selection
• Individuals with either extreme variation are selected for.
• Individuals with the average form are selected against.
• This can lead to two different species over time.
Glogster Assignment for Sec. 3
• You and a partner are going to create a glogster explaining your assigned term.
• Include: explanation/definition, examples, pictures, big idea, your own definition

Concepts:

1. Speciation

2. Morphology

3. Biological Species Concept

4. Geographic Isolation/Reproductive Isolation

5. Prezygotic Isolation/Postzygotic Isolation

6. Punctuated Equilibrium