3 Major factors that alter allele freq’s and bring about evolutionary change 1. Natural Selection – alleles passed to next generation in proportions diff from freq in present generation. * Individuals with variations are better suited to their environment and tend to produce more offspring than those less suited.

3 Factors 2. Genetic Drift – unpredictable fluctuations in allele freq (small pop = greater chance for genetic drift). *Random, non-adaptive change in allele freq 2 Examples : A. Founder effect – a few individuals become isolated from larger pop and establish a new pop whose gene pool is NOT reflective of original pop. (Amish) B. Bottleneck effect – sudden change in environment (earthquake, flood, fire, etc) drastically reduces size of pop. Few survivors that pass through restrictive bottleneck may have a gene pool that no longer reflects the original pop gene pool. (cheetah, giant panda, etc)

Founder Effect

Bottleneck Effect

3 Factors 3. Gene Flow – when pop gains or loses alleles by genetic additions or subtractions from pop. *movement of fertile individuals or gametes. *tends to reduce genetic diff between pop’s thus making pop more similar.

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While systematics is the reconstruction and study of evolutionary relationships, classification refers to how we place species and higher groups in the taxonomic hierarchy. To understand why the two are not always congruent, we need to consider how species may be grouped based on their phylogenetic (evolutionary) relationships. A monophyletic group incudes the most recent common ancestor of the group and all of its decendants. In the figure below, Taxon 1 (consisting of the seven species B-H) is a monophyletic group. It is made up of an ancestral species (species B) and all of its descendant species. A paraphyletic group includes the most recent common ancestor of the group, but not all its descendants. Taxon 2 consists of an ancestor (A) and some, but not all, of that ancestor's descendants (Taxon 2 includes the descendants I and K, but excludes J and B-H, which are also descended from A). A polyphyletic group does not include the most recent common ancestor of all members of the group. Taxon 3 is polyphylectic, which means that it lacks the common ancestor (B) that would unite the species as monophyletic group. In other words, a polyphyletic group has members that can be traced to separate ancestors.