Breeding Bunnies Lab Observe the graph and discuss with your lab mate. What is the data showing? Does it make sense? Why?

Population Genetics and Speciation

MISCONCEPTION ALERT Individuals DO NOT evolve! Individuals do not change to match changes in the environment POPULATIONS are acted upon by natural selection, where less fit individuals are less likely to pass on their genes This causes a change in the genetic make-up of the population as a whole

Genetic Variation within Populations A healthy population is one with a wide range of genetic diversity, without which evolution CANNOT occur A wide range of genetic diversity causes there to be many different phenotypes

Genetic Variation within Populations The greater the variation in phenotypes, the more likely it is that some individual can survive in a changing environment Genetic variation is stored in a population’s gene pool – the combined alleles of all the individuals in a population An allele frequency is a measure of how COMMON a certain allele is in a population

Genetic Change within Populations Genetic change can occur because of the variations within populations Genetic change causes a shift in the allele frequencies of certain traits Genetic change within populations over time can occur in several ways…

Mechanisms of Genetic Change Over Time (Evolution) Natural Selection Occurs when nature selects for or against certain traits

Mechanisms of Genetic Change Over Time (Evolution) 2. Gene Flow When genes are added or removed from a population Caused by migration (emigration or immigration)

Mechanisms of Genetic Change Over Time (Evolution) Genetic Drift A CHANCE event that can cause the allele frequencies in a population (especially a small population) to change drastically Can be caused by natural disasters such as fires, volcanoes, earthquakes and floods Why?

Genetic drift (random)

Mechanisms of Genetic Change Over Time (Evolution) 4. Non-Random Mating The cost of reproduction between males and females is different Males produce many sperm continuously, while females are born with the number of eggs that they have This allows females to be more choosy when it comes to selecting a mate Non-Random mating occurs because certain traits in males increase mating success

Mechanisms of Genetic Change Over Time (Evolution) 5. Mutations A random mutation can add a new allele to a population

Patterns of Natural Selection When natural selection is NOT occurring, most populations have a normal distribution If you were to collect one shoe from each student in your class and ordered and grouped them by size, you would probably form a hill-shape curve shown below, also known as normal distribution

Patterns of Natural Selection When natural selection DOES occur, populations can respond in three major ways…

Patterns of Natural Selection In directional selection, the “peak” of a normal distribution moves in one direction along its range In this case, selection acts to eliminate one extreme from a range of phenotypes

Patterns of Natural Selection In stabilizing selection, the bell-curve shape becomes narrower In this case, selection eliminates individuals that have alleles for any extreme type

Patterns of Natural Selection In disruptive selection, the bell-curve is pushed apart in two peaks. In this case, selection acts to eliminate individuals with average phenotype values

Speciation Through Isolation Do you remember what defines a species? A species is defined as a group of organisms that can successfully interbreed It is important to remember that species are not permanent, stable things…

Speciation Through Isolation If gene flow between two populations stops for some reason, the populations are said to be isolated As these populations adapt to their different environments, their gene pools may change All of these changes add up over generations

Speciation Through Isolation With time, the isolated populations become more and more genetically different from each other and may no longer be able to mate with each other (they become reproductively isolated) Reproductive isolation between populations is the final step of becoming separate species

Speciation Through Isolation The rise of two or more species from one existing species is called speciation There are three ways in which population may become isolated Behavioral Isolation: Caused by a difference in mating behaviors Geographic Isolation: Involves physical barriers that divide a population into 2 or more groups Temporal Isolation: Exists when timing prevents reproduction between populations

Which type of isolation is this? GEOGRAPHIC

Convergent vs. Divergent Evolution Convergent Evolution Occurs when different species evolve in similar environments When this occurs, the different species often evolve to have similar traits These traits are said to be ANALOGOUS

Examples of Convergent Evolution Bird Insect ANALOGOUS STRUCTURES! (circle them in your notes!) Dolphin Shark

Convergent vs. Divergent Evolution Occurs when closely related species evolve in different environments When this occurs, the similar species evolve to have different traits These traits are said to be HOMOLOGOUS

Examples of Divergent Evolution HOMOLOGOUS STRUCTURES!

Coevolution The process in which two or more species evolve in response to changes in each other Species that involve predator-prey or parasite-host relationships often develop adaptations in response to each other