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Population Genetics and Evolution

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Natalie Crosby

on 29 April 2013

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Transcript of Population Genetics and Evolution

•Members of a species can interbreed & produce fertile offspring
•Species have a shared gene pool
•Gene pool – all of the alleles of all individuals in a population
•Different species do NOT exchange genes by interbreeding
•Different species that interbreed often produce sterile or less viable offspring e.g. Mule The Gene Pool Populations •A group of the same species living in an area
•No two individuals are exactly alike (variations)
•More Fit individuals survive & pass on their traits Evolution by Natural Selection •Natural selection – the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do
•Evolution – a heritable change in the characteristics within a population from one generation to the next
•Adaptation – an inherited trait that increases an organism’s chance of survival and reproduction in a certain environment Environmental Science Population Genetics Speciation •Formation of new species
•One species may split into 2 or more species
•A species may evolve into a new species
•Requires very long periods of time Theories •In science, theories are statements or models that have been tested and confirmed many times.
•In science, the term "Theory" does not express doubt.
•They explain a wide variety of data and observations
•They can be used to make predictions
•They are not absolute, can be changed as new evidence is found Darwin's Travels •Charles Darwin developed the THEORY OF EVOLUTION BY NATURAL SELECTION which explained how organisms changed over time (ADAPTED)
•Darwin was a naturalist (what we today call biologists)
•He traveled the world and made observations and sketches of many species
•His most famous travels were aboard the H.M.S. Beagle where he traveled to the Galapagos Islands Darwin's Observations •Darwin noted that there existed many finches on the islands, but while they had similarities, each was adapted to eating a particular type of island food
•He concluded that the finches all came from one ancestral species and evolved into many new species
•Darwin published his work to explain the variety of species that exist on the planet
•He proposed the “Theory of Evolution by Natural Selection” Natural Selection Process 1. Variation exists among individuals in a species.
2. Individuals will compete for resources (food, mates, and space)
3. Competition would lead to the death of some individuals while others would survive
4. Individuals that had advantageous variations are more likely to survive and reproduce.
•This process came to be known as Natural Selection
–The favorable variations are called Adaptations For Example.... •Say in a species of blob….there exists blobs of all shapes and sizes (variation)
–Blobs eat the little purple organisms that live underground and on the surface.
•During a particularly hot year, food became less abundant (competition), blobs that had the ability to dig into the soil to get food had a better chance of survival.
–Many blobs died that year…….
•The ones that survived mated and passed their genes to the next generation. (reproduction)
•The next generation had move blobs with the pointed noses. That is NATURAL SELECTION. Natural Selection •Variation
•Reproduction Support for Darwin's Theory Fossil Evidence Anatomical Evidence:
Homologous Structures Anatomical Evidence:
Vestigial Organs Biochemistry and DNA Fetus Development Direct Observation of
Species Change Fossil Evidence •Shows numbers of extinct animals
•Shows similarities between extinct animals and animals that are alive today
•The earth’s layers show a time scale of species and when they appeared on earth (and when they died out)
•Example: fossils of shells, insects, whale bones, etc Anatomical Evidence:
Homologous Structures •Homologous structures – these are parts of the body that are similar, but have different functions
•Ex. The flippers of whales, and the wings of birds
•All forelimbs of vertebrates have the same pattern of bones
–Common ancestry Anatomical Evidence:
Vestigial Organs •Vestigial Organs – these are organs or parts that seem to have no function
•Whales have pelvic bones that do not attach to any legs
•The appendix and the human tailbone (coccyx) Biochemistry and DNA •When comparing the DNA of one species to another, more similarities are found in species that are more closely related. Fetus Development •Embryos of different species develop in almost identical ways. Direct Observation of Species Change •Bacteria become resistant to antibiotics
•Wolves were bred over many generations to become dogs (artificial selection) • and then bred further to create a variety of breeds Modern Evolutionary Thought Modern Synthesis Theory •Combines Darwinian selection and Mendelian inheritance
•Population genetics - study of genetic variation within a population
•Emphasis on quantitative characters
•1940s – comprehensive theory of evolution (Modern Synthesis Theory)
•Introduced by Fisher & Wright
•Until then, many did not accept that Darwin’s theory of natural selection could drive evolution Modern Synthesis Theory Today’s theory on evolution:
Recognizes that GENES are responsible for the inheritance of characteristics
Recognizes that POPULATIONS, not individuals, evolve due to natural selection & genetic drift
Recognizes that SPECIATION usually is due to the gradual accumulation of small genetic changes Microevolution •Changes occur in gene pools due to mutation, natural selection, genetic drift, etc.
•Gene pool changes cause more VARIATION in individuals in the population
•This process is called MICROEVOLUTION
•Example: Bacteria becoming unaffected by antibiotics (resistant) http://app.discoveryeducation.com/player/view/assetGuid/394121AC-2256-43A7-8F70-367D66017CFC Charles Darwin's Journey to the Galapagos Islands
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