Evolution and Phylogeny Flashcards

EVOLUTION

• Evolution is the change in the inherited traits of populations of organisms over many generations.
• It is descent with inherited modification.

PHYLOGENY

• Phylogeny refers to the evolutionary history of a species or group of organisms; it's essentially a family tree.

CLADE

• A clade is a grouping that includes a common ancestor and all the descendants (living or extinct) of that ancestor.

Domains of Life

• Archaea: Single-celled organisms lacking a nucleus and other membrane-bound organelles, similar to bacteria but with unique biochemical and genetic characteristics.
• Bacteria: Single-celled prokaryotes lacking a nucleus and other membrane-bound organelles but with different genetic and biochemical traits than Archaea.
• Eukarya: All organisms whose cells have a nucleus and other membrane-bound organelles, including plants, animals, fungi, and protists.

Phylogenetic Trees

• Phylogenetic trees are constructed by analyzing shared characteristics, primarily DNA and protein sequences, to determine how closely related organisms are.
• Taxon: Represents the evolutionary relationships among a set of organisms or group of organisms (taxa).
• The tips of the tree represent groups of descendant taxa, often species.
• Nodes of the tree represent the common ancestors of descendants.
• Two descendants that split from the same node are called sister groups.
• Outgroup: A taxon outside the group of interest, used as a reference point.

Phylogeny vs. Evolutionary Tree vs. Phylogenetic Tree vs. Cladogram

• Phylogeny: The actual evolutionary history/relationships among species or groups of organisms (a concept or hypothesis, not a diagram).
• Evolutionary Tree: A general term for any branching diagram that represents evolutionary relationships.
• Phylogenetic Tree: A diagram that represents a hypothesis about the evolutionary relationships among organisms.
• Cladogram: A type of phylogenetic tree that shows only the branching order/relationships, not time or amount of change.

Common Ancestor

• A common ancestor is an ancestral organism shared by two or more groups of organisms.

Key Points about Interpreting Phylogenetic Trees

• Phylogenies are like trees, not ladders; lineages may split and diverge.
• Reading phylogenies from left to right has no correlation with the level of advancement. The order is arbitrary.
• For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left might be arbitrary; these phylogenies are equivalent.

Homology vs. Analogy

• Homologies: Traits with the same origin but potentially different functions.
• Analogies: Traits that have similar functions but evolved independently due to convergent evolution.

Divergent vs. Convergent Evolution

• Divergent Evolution: When two or more species evolve from a common ancestor, becoming more different over time.
• Often involves structures similar in underlying anatomy but differing in function.
• Convergent Evolution: When unrelated species evolve similar traits independently, often due to similar environmental pressures.

Clades

• To group organisms into clades, use shared ancestry as the basis for classification.
• Incorporate molecular and morphological evidence.

Representing Time and Extinction on Evolutionary Trees

• Time is generally represented by branch lengths, where longer branches often indicate a greater amount of time since the branch point.
• Extinctions are usually represented by branches that end before the tip of the tree, indicating that the lineage represented by that branch is no longer extant.

Mechanisms of Evolution

• Mutation
• Migration/Gene Flow
• Genetic Drift
• Natural Selection

Mutation

• Mutations are changes in an organism's DNA sequence.
• They are the source of new genetic variation, providing the raw material for evolution.
• Mutations can be harmful, but they can also lead to beneficial traits that are favored by natural selection.
• Mutations occur spontaneously at a low rate, but they can be accelerated by environmental factors like radiation or certain chemicals.

Migration/Gene Flow

• Gene flow is the transfer of genetic information between populations.
• It occurs when individuals move from one population to another and reproduce there, or when gametes (like pollen) are transported between populations.
• Gene flow tends to make populations more similar to each other by introducing new alleles or increasing the frequency of existing ones.

Genetic Drift

• Genetic drift is a random change in allele frequencies due to chance events, particularly in small populations.
• It can lead to a loss of alleles or the fixation of alleles that are not necessarily adaptive.
• For example, if a small number of individuals from a population start a new colony, the genetic makeup of the new population may not be representative of the original population due to chance.

Natural Selection

• Individuals with traits that make them better adapted to their environment are more likely to survive and reproduce.
• These advantageous traits are passed on to the next generation, leading to an increase in the frequency of those traits in the population.
• Natural selection acts on existing genetic variation, favoring traits that enhance survival and reproduction in a particular environment.