Evolutionary Processes

Human Chromosomes

Evolution

• Evolution is change in gene (allele) frequencies in populations over time.

Species

Species: a group of organisms that, under normal circumstances, can breed with each other and have viable, fertile offspring.

Dogs and Wolves = Same Species

Horse x Donkey =

Mule

• Mules are a hybrid species. While they have positive features of both parents they are almost always sterile: i.e. they cannot reproduce;

(male) Lion x (female) Tiger

Ligers

(male) Tiger x (female) Lion

Tigon

Species, Population and Evolution

Important to remember: evolution occurs within populations, NOT individuals.

Breeding Population

• Breeding populations are populations within a species that are genetically isolated from each other, typically by geography.

• Gene pool = all the genes carried by all the members of such a group.

Gene Frequency

• Gene frequency : how frequently a particular gene is found within a given population.

• For instance, you could say that 20% (or 30% or 90%) of a population carry a particular gene (allele)

Means of Evolution

• Mutation• Natural Selection• Genetic Drift• Gene Flow• Artificial Selection

Mutation and Evolution

• Mutations are random changes in genetic material that occur within individuals.

• Mutations are what allow for the emergence of new traits within a population.

Natural Selection

• Natural selection: certain traits provide an advantage in a particular environment. Individuals with such traits are more likely to pass on their genes to offspring.

• Natural selection is sometimes summarized as “the survival of the fittest.”

Genetic Drift

Genetic drift represents changes in gene frequencies due to random chance.

Example of Genetic Drift: The Founder’s Effect

Original Population = 50% Blue eyes and 50% Brown eyes

From this group a small population separate. Coincidentally, there is a high frequency of

brown eyes in this group

New Group= 80% Brown Eyes and 20% Blue Eyes

Gene Flow and Evolution

Gene Flow: when new individuals enter a breeding population and add their genes to the gene pool.

Artificial Selection

• Artificial Selection represents breeding other organisms in order for them to display particular traits.

Speciation

• Speciation refers to the emergence of two or more species from a common ancestor.

• Species represent genetically isolated groups because of their inability to breed with each other.

Language exercise

• Italian: Pietra• Portuguese: Pedra• Spanish: Piedra• Catalan: Pedra

Language exercise

Latin: Petra Italian: Pietra Portuguese Pedra Spanish: Piedra Catalan: Pedra

Common Ancestor

• Common ancestor: the ancestor of two or more different species.

Shared derived characteristic

• Shared derived characteristic: features shared by two or more taxonomic groups that are derived from a common ancestor.

Horse

Onager

Zebra

Donkey

Hyracotherium fossil

Evolution of Equines

“Zonkey” (Zebra-Donkey Hybrid)

Homologous Structures

Analogous Structures