(4) Classification and Evolution Flashcards
What is a classification system
Arranges species into groups based on evolutionary origins, close relationships and common ancestors.
Useful to identify species, predict characteristics and establish evolutionary links.
Taxonomic hierarchy
Domain, kingdom, phylum, class, order, family, genus, species.
Species - 2 individuals breed to produce fertile offspring.
Fewer organisms in each group, going down.
Binomial naming system
Includes its genus (with capital letter), species (in lowercase) and the entire name should be written in italics or underlined.
Homo sapiens
Helps to avoid confusion of using common names, one organism might have 100 different species with the same name.
Five Kingdoms
Original classification system - using observable characteristics
Prokaryote - (bacteria), no membrane bound organelles, unicellular.
Protoctista - (algae), membrane bound organelles, uni/multicellular.
Fungi - (mould), membrane bound organelles, uni/multicellular, chitin cell wall.
Plantae - (flowering plants), membrane bound organelles, multicellular, cellulose cell wall.
Animalia - (mammals, fish), membrane bound organelles, multicellular.
New evidence for calssification
Based off other evidence: DNA (base sequence of genes, the sequence of amino acids in protein),
behaviour (social organisation),
anatomical (structure/function of body parts).
embryological (early stages of development)
3 Domains of life
bacteria and archaea (prokaryotes)
eukarya (protoctista, plantae, fungi, animalia - organisms with a nucleus)
why:
RNA polymerase is different in bacteria and archaea,
histones are similar in archaea and eukarya,
ribosomes are larger in eukarya,
protein synthesis, the first amino acid synthesised is different in eukarya.
Phylogeny
Phylogenetics - study of the evolutionary history of organisms.
Phylogenetic trees represent the evolutionary relationship between organisms and they show that different species evolve from the same common ancestor. Closely related species diverges away from each other more recently - branches are closer together.
Species is the smallest group that shares the common ancestor - phylogenetic species.
Classifying organisms in this way - cladistics.
Advantages: produces a continuous tree, whereas classification requires discrete taxonomic groups. Classification can be misleading
Different types of variation
Intraspecific - variation within species.
Interspecific - variation between species.
Continuous variation - when individuals in a population vary within a range, no distinct categories. Polygenic
Examples : milk yield in animals or mass in humans, number of leaves on a plant, or the width of a bacteria or length of the flagellum.
Discontinuous variation - 2 or more distinct categories and an individual can only fit into one. Controlled by one genes.
Examples : blood group in humans, colour of plant or seed shape, antibiotic resistance in microorganisms.
Genetic causes of variation
Different species have different genes. Differences in genotype cause differences in phenotype, which can be observed. Blood groups in humans are caused by different alleles on specific genes which are inherited.
Sexual reproduction and meiosis also causes variation - independent assortment (metaphase 1) and crossing over (prophase 1)
Mutations - causing changes in the proteins that are being coded for.
Chance.
Environmental causes of variation
Climate, food, lifestyle.
Characteristics controlled by the environment can change over time, for example piercings, or accent.
Plants may be affected by the environment to a greater degree because they cannot move.
Environmental and genetic cause
Most variation is caused by an interaction of both genetics and environment. For example, height may be determined by genes, but a more diet will affect the expression of the gene.
Representing variation graphically
Darwin’s theory of evolution
Realised that organisms best suited the environment are more likely to survive and reproduce. These traits are then passed on to future generations by genes and gradually a species changes over time to have a more advantageous phenotype.
This leads to evolution because the favourable characteristics become more common in a population.
Selection pressures - predation, disease and competition. Those without advantageous characteristics are less likely to survive and have reproductive sucess.
Examples : peppered moths, antibiotic resistant bacteria.
Evidence for evolution
Fossils - remains of organisms preserved in rocks, different layers of rock correspond to different geological eras, so they can be arranged in chronological order to observe gradual changes.
Simplest organisms are found in the oldest rock. It also allows us to investigate relationships between extinct organisms and living ones.
However the fossil record is not complete, some organisms may have died without being preserved.
Homologous structures - appear superficially different and may perform different actions (limb).
DNA - evolution is caused by gradual changes in the base sequence of DNA. Organisms that diverged from each other more recently should have more similar DNA as less time has passed for changes to occur. Can also look at mitochondria DNA.
Molecular evidence - comparing sequence of amino acids in proteins, (cytochrome c), the order of DNA bases or compare antibodies. Then scientists can then estimate the point at which the 2 species last shared a common ancestor. Those who are distantly related have far fewer similarities. Ribosomal RNA has a slower rate of substitution so can be used to compare relationships in ancient species.
Different types of adaptations
Increase organisms chance of survival
Behavioural
Anatomical
Physiological
