Genetics and Evolution
A Bell Curve
Directional Selection
Stabilizing Selection
Disruptive Selection
What did Darwin know about Genetics?
What did Darwin know about Genetics?
• Nothing!
Population Genetics
• Population Genetics = the study of evolution from a genetic point of view.
What Causes Variation?
• 1) Mutations • 2) Recombination during meiosis (crossingover) • 3) Random fusion of gametes (out of millions of sperm only one fuses with the egg)
Allele Frequency
• The number of a certain allele/ number of total alleles
– So if half of the gametes out of five gametes carries the A gene then the allele frequency is 50%
Phenotype Frequency
• The number of individuals with that phenotype divided by the total number of individuals in the population • Example:
– Attached earlobes: recessive – Unattached earlobes: dominant – Calculate the class’s phenotypic frequencies for earlobes
Hardy-Weinberg Genetic Equilibrium
• Based on assumptions about a hypothetical population
– No net mutations occur – Individuals don’t come or leave a population – A population is very large – Individuals mate randomly – Selection doesn’t occur
Genetic Drift
• Allele frequencies in a population change as a result of random events or chance • This happens to small populations more often than large populations
Phenotype & Genotype
• What does natural selection act on? Phenotype or Genotype?
Phenotype & Genotype
• What does natural selection act on? Phenotype or Genotype?
– Natural Selection acts on the phenotype of an organism NOT on the genotype.
Recessive genes
• Recessive genes can get passed on in a population without being acted on by natural selection • Ex) Hemophelia
What is a species?
• A population of organisms that can successfully interbreed but can’t breed with other groups
Speciation
• Speciation is the formation of a species • How does this happen?
Speciation & Geographic Isolation
• One common way to form a species is through geographic isolation. • There are two species of squirrels who live on opposite sides of the Grand Canyon (A harrisi and A leucuros). They are very similar but no longer the same species.
– How did this happen?
Other ways a species can form
• Mating habits can change (Behavioral Isolation)
– Ex) Some birds within a species will accept only one song. Other birds accept a different song. Eventually these will become two species
• Species mate at different times of day or of the year (Temporal isolation)
– Ex) Within a species of frogs some mate at night some in the morning. After time these will become two species
The Peppered Moth
• The peppered moth is a species of night-flying moth.
The Peppered Moth
• Originally, the vast majority of peppered moths had light colored which effectively camouflaged them against the light-colored trees. • During the Industrial Revolution there was widespread pollution in England. The trees the moths rested on all became blackened by soot. • So What happened?
The Peppered Moth
• Originally, the vast majority of peppered moths had light colored which effectively camouflaged them against the light-colored trees. • During the Industrial Revolution there was widespread pollution in England. The trees the moths rested on all became blackened by soot. • So What happened? The light colored moths died off due to predation. At the same time the dark colored moths flourished because of their ability to hide on the darkened trees.