Biology Evolution Revision PDF

Biology - Evolution Oscar Tuckwell  Variation - The diversity phenotypic and genotypic traits in a given population Affected by( sexual reproduction, mutations, environment ) Species A species is a group of organisms with similar characteristics that can reproduce to c...

Biology - Evolution Oscar Tuckwell  Variation - The diversity phenotypic and genotypic traits in a given population Affected by( sexual reproduction, mutations, environment ) Species A species is a group of organisms with similar characteristics that can reproduce to create fertile offspring Gene pool Total sum of all the different types of genes in all individuals of a population. adaptation An inherited trait which increases organisms' sexual reproduction and survival  Allopatric Speciation Steps (VISS) 1. Variation, all populations show different degrees of variation 2. Isolation, a population get split into two via a geographical barrier, interbreeding between the two stops 3. Selection, different selection pressures favour different characteristics in each sub -population. The gene pools change independently of each other. Mutations in one population are not seen in the other, which causes more variation. The smaller the population, the faster evolution occurs 4. Speciation, eventually, the two populations accumulate enough genetic differences that they can no longer produce fertile offspring, they are then different species Speciation The formation of two or more new species from one species  Mutation - Mutations are random permanent changes to an organism’s DNA sequence - The effect of a mutation varies on whether it occurs in germline (reproductive) or somatic (body) cells Two mechanisms for phenotype -genotype -enviroment  Mutagens - A mutagen is an environmental or physical factor which can increase the frequency of mutations Somatic cell mutations Mutations in somatic cells only affect daughter cells and itself  Selection Pressures - Selection pressures are any feature of the environment that favours one characteristic over another How Natural Selection Leads to Evolution - There is variation in populations - More individuals are produced than can be suppor ted - There is a struggle for sur vival /resources - Individuals with favourable characteristics out-compete individuals lacking favourable characteristics - The individuals with favourable characteristics sur vive - Sur vivors reproduce and pass on favourable characteristics - There is an increase in the favoured allele in the gene pool Selection pressures Any feature of the environment that favours one characteristic over another Mutations in germline cells Mutations here affect gametes and get inherited in subsequent offspring  Effects of Mutations on Survival - There are three types of mutations that affect the survival of an organism - Neutral mutations are where the protein product is unchanged, and an organism’s survival is unaffected - Deleterious mutations negatively affect an organism’s chance of survival by disrupting a protein’s function - Beneficial mutations are uncommon, but they positively affect an organism’s chance of survival  Natural Selection - Natural selection is Darwin’s idea about evolution - Natural selection is the process where organisms with beneficial adaptations for their environment survive and reproduce, passing on these characteristics  Gene Pool - The gene pool is the total sum of all different types of genes in all members of a population  Geneflow The movement of genes from one population to another through interbreeding Introduces new gene into a population Make populations more genetically similar.  Darwin’s 3 Main Ideas (VBN) - 1. Variation – All members of a species shows variation - 2. Birth Rate – There is always a higher birth rate than availability of resources allows (generally food) - 3. Nature’s Balance – Despite a high birth rate, population numbers stay constant  Adaptation over Time - Environments change over time - Favourable characteristics also change - The gene pool also changes and the population evolves further  Micro-evolution Small changes within a single population over successive generations, short time -subtle changes in in the frequency of a gene in a population Macro evolution The accumulation of micro evolutionary changes resulting in a macro evolutionary change , which can lead to the formation of a new species , over a long time Accumulation Process in which inherited traits are selected and inherited, becoming more frequent in the gene pool.  Lamarck’s Theory of Evolution - Lamarck believed that if an organism used a characteristic in its lifetime, it would become stronger, and this would be passed on to their offspring - Example: Giraffes stretched their heads to reach high leaves, their necks would grow longer, and they would pass this trait onto their offspring  Allopatric Speciation key points 1. Variation population 2. geo barrier causes separation 3. Gene flow between two sub populations 4. Diff selection pressures in each population 5. Each population evolves isolated from one another 6. Eventually gene pool accumulated so many differences that they are no longer same species, no longer interbreed to form fertile offspring.  Artificial Selection - Artificial selection is the selection of plants or animals with desirable characteristics by humans to breed in the hope of producing more offspring with these characteristics - This process is repeated over numerous generations to generate results  Artificial Selection Steps 1. Humans select two parents with desirable traits 2. Parents bred together 3. Some offspring inherit desirable traits 4. Offspring with best traits are chosen to breed next generation 5. The process is repeated 6. Each time, the desired traits become more pronounced in offspring  Desirable Characteristics - Disease resistance - Faster growth rate - Higher yield - Tolerance to adverse conditions - Improved product quality - More meat on body  Fossils - Fossils are preserved remains and traces of organisms from over 10,000 years ago - There are four types of fossil - The conditions to form a fossil include a lack of decomposers, absence of O2 and absence of H2O - Low temperature  The Four Types of Fossil - Trace – Trace fossils capture the activities of organisms, examples include footprints, trails, and burrows - True form – true form fossils are the actual organism or parts of it. Examples include mosquitoes in amber or old skulls - Mould – Mould fossils are imprints or impressions lef t by an organism that hardens to form a hollow imprint of the organism. An example is a mould of a seashell in a rock - Cast – Cast fossils are formed when a mould fossil is filled with sediment, creating a replica of the original organism’s shape. An example is a cast of a seashell in a seashell mould  Cast Fossil Formation Steps 1. An animal dies, its skeleton settles onto the seafloor and is buried by sediment 2. The sediment surrounding the skeleton thickens and turns to stone 3. The skeleton is dissolved by groundwater and a mould is formed 4. Minerals from the groundwater crystallise inside the mould and a cast is formed 5. Fossil is exposed on the Earth’s surface due to erosion 5 Ways Fossil Record is Evidence for Evolution - It shows changes in an organism’s structure over time (natural selection) - Organisms in the fossil record have become more complex over time - The variety of fossils increases in the upper, more recent, layers of the rock - No fossil record exists of any modern organisms - Missing links, common ancestors  Superposition - Superposition is the idea that layers at the top of a rock are younger than the one directly beneath them  Correlation of Rock Strata - Matching layers of rock from different areas can be from the same period - Rocks that contain the same type of fossils can be assumed to be the same age Eevidence for evolution- comparative anatomy - Ve s t i g i a l s t r u c t u r e s a r e o r g a n s t h a t d u r i n g e vo l u t i o n h ave r e d u c e d i n s i z e a n d / o r lost their function - This shows evidence of ancestors where structure had a function Evidence for evolution – comparative embryology - Comparative embryology is where some vertebrates possess traits that are present in the embryos but not in the adults of the organism - These traits had a function in organism’s ancestors but not in the adult stage of these organisms - This suggests that they had a common ancestor  Characteristics Vertebrae Share - Pharyngeal slits (filter feeding) - Absence of paired appendages (arms and legs) - Well-developed post-anal tail - 2-chambered heart - Similar levels of brain development  Homologous Structures - Organs with similar structure but not a similar function (organism to organism) Suggests that organisms have common ancestors with that structure Thus, shows common ancestry The Pentadactyl Limb - Not necessarily best structure for all organisms - 1-2-5 Formation (Penta=5) - One bone in upper arm and two bones in the forearm and 5 digits  Comparative DNA - All living things use the same DNA code (A -T C-G) - DNA sequence varies between organisms - When speciation has first occurred, two new species would have very similar DNA - The longer two groups are separated from a common ancestor, the more differences they have  Comparative DNA cont. - The Human Genome has 3.1b base pairs - 2% different = 62m differences