Speciation 17 & 18

Selection : 

Selection

Natural SelectionDarwin’s theory : 

Natural SelectionDarwin’s theory Charles Darwin proposed a theory which did not rely on a supernatural theory to explain why beings exist. He explained that we had arisen from a primitive common ancestor millions of years ago. He suggested that we had evolved through a series of changes.

Natural selectionDarwin’s theory : 

Natural selectionDarwin’s theory NATURAL SELECTION is the survival of organism that are best suited to their environment. These individuals then pass on their advantageous genes too their offspring = basis of EVOLUTION He noticed various stages leading to the ‘weeding out’ of organisms: Overproduction- a species produced more offspring than can actually survive. Variation- resulting from Mutation, Independent assortment, crossing over, and multiple alleles. Selection pressures- abiotic, and biotic.

Natural SelectionExamples : 

Natural SelectionExamples Malanic moth at a selective advantage

Speciation : 

Speciation A species is a group of organisms that share a common gene pool: All the alleles present in the species may be divided into different populations Isolating Mechanisms: Geographical Ecological Reproductive Mechanisms of Speciation ISOLATION> MUTATION> NATRUAL SELECTION> NEW SPECIES!

Adaptive Radiation : 

Adaptive Radiation This is the evolution of many new species from a common ancestor Each new species is specifically suited to surviving in it’s environment. It takes place over a long period of time (Usual speciation method takes place). An individual that has a selective advantage is more likely to survive when conditions change The finches evolved to fill the available ecological niches. The lifestyle an organism has within a particular ecosystem

Adaptive Radiation : 

Adaptive Radiation Homology Structures are said to be HOMOLOGOUS if they have the same evolutionary origin and are structurally alike. Divergent Evolution A group of animals that have undergone adaptive radiation possess homologous structures. In the course of evolution the structure has become adapted to suit different functions, this is called DIVERGENT EVOLUTION. Convergent Evolution Some animals possess similar structural features and may even resemble one another closely although they are from different evolutionary origins. This is because each has become adapted to suit the same ecological niche, so therefore have similar structures, this is called CONVERGENT EVOLUTION.

High Speed Evolution : 

High Speed Evolution Bacteria can reproduce rapidly which allows them to become resistant to antibiotics quickly. They do this by: A mutant bacterium is already resistant. Antibiotics taken and resistant bacterium remains. Resistant bacteria reproduces new population of resistant bacteria. In addition to the transmission of the gene for antibiotic resistance from one generation to the next, drug resistance can be passed from one bacterium to another in a plasmid during a process of CONJUGATION. Bacterium resistant Non- resistant bacterium Plasmid about to pass through tube with resistance gene It is therefore possible for harmless bacterium to receive a disease causing bacterium due to the passing of the plasmid through the conjugation Conjugation

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