Variation, Adaptation + Evolution

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Types of Variation

Continuous Variation

  • when the individuals in a population vary within a range - there are no distinct categories e.g. height, weight, skin colour

Discontinuous Variation

  • when there are two or more distinct categories - each individual falls into only one of these groups e.g. gender, blood group
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  • individuals in the same species have different genotypes
  • this variation in genotype results in variation in phenotype
  • some characteristics are controlled by only one gene (myogenic) they tend to show discontinuous variation
  • most charcteristics are controlled by a number of genes at different loci* - they're polygenic and usually show continuous variation

*different alleles for the same gene are found in the same position on chromosomes - the locus

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Some characteristics are only influenced by geneotype (e.g. blood group) but most characteristics are influenced by both genotype and the environment (e.g. weight).

  • height is polygenic and affected by environmental factors, especially nutrition e.g. tall aprents usually have tal children, but if the children are undernourished they won't grow to their maximum height, as protein is required for growth
  • monoamine oxidase A (MAOA) is an enzyme that breaks down monoamines in humans - low levels of MAOA have been linked to mental health problems - its production is controlled by a single gene (it's monogenic) but taking anti-depressants or smoking tobacco can reduce the amount produced
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  • cancer is the uncontrollable division of cells that leads to tumours forming, the risk of developing some cancers is affected by genes, but environmental factors such as diet can also influence the risk
  • animal hair colour is polygenic, but the environment also plays a part in some animals  e.g. some animals have dark hair in the summer but white hair in the winter - environmental factors like decreasing temperature triggers  this change but it couldn't happen if the animal didn't have the genes for it
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  • the niche a species occupies within a habitat includes its interactions with other living organisms, and the non-living environment
  • every species has its own unique niche - a niche can only be occupied by one species
  • it may look like two species are filling the same niche, but there will be slight differences
  • if two species try to occupy the same niche, they will compete with eachother - one species will be more successful than the other, until only one of the species is left
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Adapting to Niche

Adaptations are features that increase an organisms' chance of survival and reproduction. All species have adaptations that allow them to use their environment in a way that no other species can - they're adapted to their niche.

  • behavioural adaptations are ways an organism acts e.g. male bats make mating calls to attract female bats
  • physiological adaptations are processes inside an organisms body e.g. bats lower their metabolism in order to hibernate over the winter, allowing them to conserve energy when food is scarce
  • anatomical adaptaions are structural features of an organisms' body e.g. bats have light, flexible wigs allowing them to hunt fast-flying insects
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Natural Selection

  • individuals within a population show variation in their phenotypes
  • predation, disease and competition create a struggle for survival
  • individuals with better adaptations are more likely to survive, reproduce and pass on their advantageous adaptations to their offspring
  • over time, the number of individuals with the advantageous adaptations increases
  • over generations, this leads to evolution as the favourable adaptations become more common in the population
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Peppered Moths

  • peppered moths show variation in colour
  • before the 1800s, there were more light moths than dark moths
  • during the 1800s, pollution had blackened many of the trees the moths lived on
  • dark coloured moths were now better adapted to this environment - they were better camouflaged from predetors, so would be more likely to survive, reproduce and pass on their dark colouring to their offspring - this caused the number of dark moths to increase
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  • taxonomy involves naming organisms and organising them into groups based on their similarities and differences, making it easier for scientists to identify and study them
  • there are seven taxanomic groups: Kingdom, Phylum, Class, Order, Family, Genus, Species
  • a species is a group of similar organisms able to reproduce to give fertile offspring
  • the binomial system gives a unique name (Latin, genus and species) to all organisms so thats scientists from all countries can communicate about organisms with minimal confusion
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Five Kingdoms

Prokaryotae: prokayotes, unicellular, no nucleus, less than 5µm e.g. bacteria

Protoctistaeukaryotic cells, usually live in water, unicellular or simple multicellular orgamisms (e.g. algae, protozoa)

Fungi: eukaryotic, chitin cell wall, saprotrophic (absorb substances from dead or decaying organisms) e.g. moulds, yeast, mushrooms

Plantae: eukaryotic, multicellular, cellulose cell walls, can photosynthesise, contain chlorophyll, autotrophic (produce their own food) e.g. mosses, ferns, flowering plants

Animalia:  eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals) e.g. fish, reptiles, mammals, birds

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Three Domain System

three domains uses molecular phylogeny (the study of the evolutionary history of groups of organisms) to look at DNA and proteins to see how closely related organisms are

in the new system, all organisms are placed into one of three domains - large superkingdoms that are above the kindoms in the taonomic hierachy

organisms that were in the kingdom prokaryotae are separated  into two domains - the archaea and bacteria, organisms from the other four kingdoms are placed in the third domain - eukarya

the prokaryotae were reclassified into two domains because molecular phylogeny suggested archaea and bacteria are more distantly related than origionally thought

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