chapter 16 the evolution of populations and speciation n.
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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.

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genetic equilibrium
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.
  • 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
Causes of Variation
  • Mutation
  • Recombination
  • Random fusion of gametes
allele frequencies and the gene p ool
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
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
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
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
Genotype Frequencies
  • Frequency of certain genotypes.


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
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
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
  • This is theoretical.
  • Hardy and Weinberg allowed us to see what disrupts equilibrium.
  • Pg. 302
  • Questions 1-6
ch 16 sec 2 nonrandom mating
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
Assortative Mating
  • Selecting mates with similar characteristics.
natural selection
Natural Selection
  • The 5th requirement for Genetic Equilibrium.
stabilizing selection
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
Directional Selection
  • Individuals with a more extreme form of a trait are selected for.
  • Allele frequencies are going in a direction.
disruptive selection
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
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


1. Speciation

2. Morphology

3. Biological Species Concept

4. Geographic Isolation/Reproductive Isolation

5. Prezygotic Isolation/Postzygotic Isolation

6. Punctuated Equilibrium