Biology 11.3 Evolution PDF

BIOLOGY 11.3 11.3.1 Evolution - is the cumulative change in heritable characteristics of a population over time. Species - a group of organisms able to interbreed producing fertile offspring that shares common characteristics Variatio...

BIOLOGY 11.3 11.3.1 Evolution - is the cumulative change in heritable characteristics of a population over time. Species - a group of organisms able to interbreed producing fertile offspring that shares common characteristics Variation is both environmental and genetic! Ties with selection pressures - variation allows some organisms to be better suited to their environment, more likely to survive and produce fertile offspring Natural selection is a key driver of evolution. Individuals with traits better suited to their environment survive longer and produce more offspring, passing on their traits All species must have evolved by divergence from pre-existing ones. 11.3.2 Evidence for evolution: Fossil record - remains of organisms which are preserved in rocks. This shows that changes have occurred over millions of years, on a vast variety of organisms radiometric dating - studying when an organisms mightve lived by studying the natural radioactivity fossils Selective breeding - humans alter the characteristics and intentionally choose desirable specific traits to breed in species, this is called artificial selection otherwise. This is done with plants and animals Work of John Endler (wild guppies) - showed that there was correlation between the colour of the guppies, with the males being less colourful where there were more predators and the more colorful guppies were located away from the predators. Endler moved predators around, essentially wiping out the colourful males as the predators ate them, removing those genes from the population BIOLOGY 11.3 1  Comparison of DNA base sequences - comparing DNA sequences from different species can highlight the similarities between them but also the differences DNA found in mitochondria - since mtDNA doesn't mix with the father's DNA and it mutates faster than nuclear DNA, it’s easier to track changes over time. This makes it useful for studying recent evolutionary relationships between species or groups within a species 11.3.3 How new species arise Speciation - is the formation of new species from an already existing population. It happens when populations of the same species become isolated and evolve differently. a population is a group of organisms of the same species that live in the same area at the same time speciation only occurs if there's some sort of barrier between the population: geographical separation such as mountains, river or a road temporal differences (mating at different times so the two populations don't breed) behavioural differences such as differentiating rituals etc so they become incompatible over time Speciation is either: sympatric - occurs in the same geographical area allopatric - occurs in different geographical areas An example of geographical separation are the bonobos and Chimpanzees Infertile hybrids - if two species do try and breed, they form a hybrid. hybrids are sterile, meaning they are not able to produce fertile offspring, this shows how speciation occurs, with the hybrid not being able to move genes from one species to another. Hybrid offspring are sterile due to the number of their parents different chromosomes, producing an odd number. Example is a mule, which has 63 chromosomes due to the parents having 64 and 62 chromosomes BIOLOGY 11.3 2  11.3.4 Gene pool - All the genetic information in a reproducing population. Changes in allele frequencies within the gene pool show that evolution is happening. Genetic Drift: Random changes in allele frequencies, often affecting small populations. This can make two isolated populations genetically different over time. Allele frequency gives us an indication of the proportion of a specific gene variant in a population Gradual Evolution: Species evolve slowly and continuously over long periods of time. Small, incremental changes accumulate in a population. Fossil records would show a smooth transition with many intermediate forms between species. Punctuated Evolution (Punctuated Equilibrium): Evolution occurs in short bursts of rapid change, followed by long periods of little or no change (equilibrium). Species remain stable for long periods, and significant changes happen quickly, often due to sudden environmental shifts. Fossil records would show abrupt appearances of new species with few or no intermediate forms. BIOLOGY 11.3 3