genetics and evolution

• in the 1800s, Darwin took an expedition around the world and collected a vast number of animals and plants, he saw looks of variety and began to wonder how this variety developed
• within any species, we see a wide range of genetic variation for any characteristic. individuals with characteristics most suited to the environment are more likely to survive to breed successfully
• the characteristics that enabled individuals to survive are then passed onto the next generation
• darwin published a book called the origin of species containing his theory, it was extremely controversial and only gradually accepted.
• darwins theory was controversial because at the time lots of people believed that god made all of the animals and plants that lived on earth, darwins theory challenged this
• darwins theory was also controversial as many scientists felt that darwin did not have enough evidence to back up his theory. people did not understand how characteristics are inherited, genetics was not understood until 50 years after darwins theory published
• jean baptiste lamarck suggested that when a characteristic is regularly used, it becomes more developed, this strengthened characteristic is then passed onto the offspring.
• jean baptiste lamarcks theory was proved wrong as characteristics that develop or change during an organisms lifetime cannot be passed onto offspring. scientists then began to accept darwin's theory
• alfred russel wallace was working on evolution at the same time as darwin. he travelled and was mostly interested in warning colouration of animals e.g. the bright red colour of frogs can warn a predator that it is poisonous
• wallace was studying how warning colours had evolved and came to the same theory as darwin, so they jointly published their findings
• wallace was very interested in how new species are formed, this is called speciation
• wallace noticed that closely related species were often separated by geographical barriers such as rivers
• speciation: e.g. if theres an island with one species of an animal, all these can interbreed so any beneficial mutations spread through the whole population. if a geographical barrier e.g. river changes course and separates the group, there is now no interbreeding between groups. overtime natural selection will favour different alleles on the 2 sides. mutations that occur cannot spread, meaning that over many generations the 2 populations will begin to change, the phenotypes become so different that they can no longer reproduce to make fertile offspring when they mix
• genes are sections of DNA on a chromosome and each gene determines the amino acid sequence of a specific protein. alleles are different versions of genes, the can be dominant e.g. the allele for polydactyl or recessive e.g. the allele for cystic fibrosis
• mendel carried out thousands of breeding experiments on pea plants and looked at lots of characteristics like the shape of the pod or colour of the flowers. mendel realised that characteristics are not blended during inheritance e.g. shape of pea pod has no effect at all on the colour of the flowers
• mendel concluded that characteristics are determined by inherited units, and that these units do not change when passed onto descendants. we now call these units genes.
• mendel also showed that some characteristics could be masked and the reappear in later generations, these are now called recessive alleles.
• mendel published his research in a scientific paper, however many scientists still believed that characteristics are blended when they are inherited, his work was forgotten until later when chromosomes were being studied
• fossils provide good evidence for evolution. they are the remains of organisms from millions of years ago which are found in rocks. they form in three ways
• fossils can form when parts of organisms cannot decay, this can happen when the conditions needed for decay are absent e.g. temperatures are too cold, not enough oxygen or water
• fossils can form even if organisms decay if parts of the organism are replaced by minerals during the decay process.
• fossils can be preserved traces of organisms e.g. animals leave footprints or burrows, plants can also leave preserved places where their roots were
• many early forms of life were soft-bodied organisms/ did not have a shell or a skeleton so they rarely formed fossils or fossils that did form were destroyed by changes to rocks in the earths crust. due to this gap, scientist cannot be certain how life on earth began
• fossils can show extinct species, a species is extinct when there are no remaining individuals of that species still alive.
• extinction can happen after a catastrophic event e.g. an asteroid colliding with the earth eventually led to dinosaurs extinction, or when the environment changes due to things like weather patterns, new diseases and new predators could also kill all individuals or if a new, more successful species evolve and competes with it
• bacteria evolves extremely rapidly under the right conditions as they can reproduce so quickly
• many people used to die from diseases caused by bacteria, however in the 1940s doctors began to treat bacterial diseases using antibiotics such as penicillin. antibiotics kill bacteria
• antibiotics are also used in farming to prevent animals from developing bacterial diseases
• in the last few years, certain strains of bacteria are no longer killed by antibiotics because they have evolved and are now antibiotic resistant. a common strain of this is MRSA
• if there is a population of bacteria, its likely there will be mutations which lead to genetic variation. it is possible that a mutation could make a bacterium resistant to antibiotics. if we use an antibiotic, all of the bacteria are killed apart from the resistant one, this will survive and reproduce without any competition so the population will rise and spread as people are not immune to it
• to prevent antibiotic resistance, doctors should not prescribe antibiotics innappropriately e.g. to use a virus. patients should make sure they use all of their prescribed antibiotics to ensure all bacteria are killed and restrict the use of antibiotics in farming
• new antibiotics are being developed but it takes a very long time ad is extremely expensive
• as species were discovered scientists realised some things that they had in common. in 1700s, carl linnaeus began to classify different species into different categories based on structure and characteristics
• linnaeus divided all living organisms into 2 kingdoms, the animal kingdom and the plant kingdom. then they are divided into smaller categories; kingdom, phylum, class, order, family, genus and species (king phillip came over for good soup).
• species are named from their genus and their species, this is called the binomial system
• the classification system is based on how species look not internally so now we use the 3 domain system; archaea, bacteria and eukaryotes