Fossil Record & Homologies  Scientists have used the fossil record to construct a history of life on Earth. This is only a theory Fossil record is not complete  Scientists have used the fossil record to construct a history of life on Earth. This is only a theory Fossil record is not complete

Homologous Body Structures  Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues

A cladogram is a theoretical evolutionary tree made using cladistics. –A clade is a group of species that are thought to share a common ancestor. –Each species in a clade shares some traits with the ancestor. –Each species in a clade has traits that have changed.

Mechanisms of Evolution There are several: 1.Natural Selection 2.Gene Flow 3.Genetic drift 4.Mutations 5.Non-random mating There are several: 1.Natural Selection 2.Gene Flow 3.Genetic drift 4.Mutations 5.Non-random mating

1. Natural Selection:  Affects variation in a population as the better adapted (more fit) individuals survive and reproduce, passing on their genes to the successive generations.  Acts only upon an organism’s phenotype (its physical characteristics).  If the phenotype is better suited for a changing environment, the individual can survive and pass on its genes.  Affects variation in a population as the better adapted (more fit) individuals survive and reproduce, passing on their genes to the successive generations.  Acts only upon an organism’s phenotype (its physical characteristics).  If the phenotype is better suited for a changing environment, the individual can survive and pass on its genes.

Natural Selection

2. Gene Flow:  Is the movement of alleles into or out of a population (immigration or emigration).  Gene flow can introduce new alleles into a gene pool or can change allele frequencies.  The overall effect of gene flow is to counteract natural selection by creating less differences between populations.  Example:  Plant pollen being blown into a new area  Is the movement of alleles into or out of a population (immigration or emigration).  Gene flow can introduce new alleles into a gene pool or can change allele frequencies.  The overall effect of gene flow is to counteract natural selection by creating less differences between populations.  Example:  Plant pollen being blown into a new area

Gene Flow

3. Genetic Drift  The change in allele frequencies as a result of chance processes.  These changes are much more pronounced in small populations.  The change in allele frequencies as a result of chance processes.  These changes are much more pronounced in small populations.

Examples of Genetic Drift  A) The Founder Effect:  Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived.  Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals.  A) The Founder Effect:  Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived.  Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals.

Examples of Genetic Drift  B) Population Bottleneck:  Occurs when a population undergoes an event in which a significant percentage of a population is killed or otherwise prevented from reproducing.  B) Population Bottleneck:  Occurs when a population undergoes an event in which a significant percentage of a population is killed or otherwise prevented from reproducing. The event may eliminate alleles entirely or also cause other alleles to be over- represented in a gene pool. EX. Cheetahs

4. Mutations:  Are inheritable changes in the genotype (genes).  Provide the variation that can be acted upon by natural selection.  Mutations provide the raw material on which natural selection can act.  Are inheritable changes in the genotype (genes).  Provide the variation that can be acted upon by natural selection.  Mutations provide the raw material on which natural selection can act.

Exp. Frog mutation

5. Non-Random Mating:  In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behavior.  Many plants self-pollinate, which is also a form of non-random mating (inbreeding).  In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behavior.  Many plants self-pollinate, which is also a form of non-random mating (inbreeding).