4: evolutionary processes
DESCRIPTION
Evolutionary Proc.TRANSCRIPT
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