A3.1

• Species


  A group of organisms with shared traits that are distinct from all others
• Diversity of genomes within and between species

  • Patterns seen in diversity
  • Asian rice (Oryza sativa) genome has up to 63,000 genes divided between 12 chromosomes
  • Different rice varieties possess different alleles but share the same 12 chromosomes and gene loci
• The first chromosome of rice shows gene loci present on it
• Variation between organisms


  A defining feature of life
• Variation between organisms


  • No two individuals are identical in all their traits
  • Patterns of variation are complex and the basis for naming and classifying organisms
• Species


  Groups of organisms with shared traits (original morphological concept used by Linnaeus)
• Binomial system for naming organisms

  • First part identifies the genus, second part distinguishes the species
  • Species in the same genus have similar traits
  • Genus name has initial capital, species name is lowercase
• Biological species concept


  A species is a group of organisms that can breed and produce fertile offspring
• Challenges associated with the biological species concept and competing species definitions exist
• Speciation


  • The splitting of one species into two or more
  • Usually happens gradually as populations become more different in their traits
  • Can be arbitrary to decide if two populations are the same or different species
• Diversity in chromosome numbers of plant and animal species

  • Humans have 46 chromosomes, chimpanzees have 48
  • Diploid cells have an even number of chromosomes
• Karyotyping and karyograms


  1. Classify chromosomes by banding patterns, length and centromere position

  2. Evaluate evidence for hypothesis that human chromosome 2 arose from fusion of chromosomes 12 and 13
• Genome


  • All the genetic information of an organism
  • Organisms in the same species share most of their genome but have variations like single-nucleotide polymorphisms
• Diversity of eukaryote genomes

  • Genomes vary in overall size and base sequence
  • Variation between species is much larger than variation within a species
• Comparison of genome sizes

  1. Extract information about genome size for different taxonomic groups from a database

  2. Compare genome size to organism complexity
• Whole genome sequencing


  • Increasing speed and decreasing costs
  • Current uses include research into evolutionary relationships
  • Potential future uses include personalized medicine
• The biological species concept does not work well with asexually reproducing species and bacteria that have horizontal gene transfer
• Chromosome number as a shared trait within a species

  • Cross-breeding between closely related species unlikely to produce fertile offspring if parent chromosome numbers are different
• Identification of species from environmental DNA in a habitat using barcodes


  Allows rapid investigation of habitat biodiversity
• Organism


  Any biological system that functions as an individual life form, composed of cells
• Population


  A group of organisms of the same species in the same area, showing variation
• Community


  Populations of two or more species occupying the same geographical area at the same time
• Discrete (Discontinuous) Variation


  Traits that can be placed into distinct categories with no in-between forms, usually influenced by a single gene
• Continuous Variation


  Traits that vary along a quantitative continuum, usually the result of multiple genes interacting and influenced by the external environment
• Sources of genetic variation within a species

  • Mutation
  • Gene flow
  • Meiosis
  • Sexual reproduction
• Genetic variation in a population

  Enables some organisms to be better suited to the environment than others, leading to their survival and reproduction, driving natural selection and evolution
• Genetic variation is heritable
• Morphology


  The distinctive shapes and forms of organisms
• Grouping organisms based on morphology has limitations due to convergent evolution
• The International Botanical Congress (IBC) and International Congress of Zoology (ICZ) oversee international efforts to maintain consistent naming conventions and use of taxa
• Naming conventions reflect evolutionary relationships and enable scientists to communicate in a common language
• The biological species concept doesn't apply to asexually reproducing species, extinct species, and doesn't account for the impact of natural selection
• Difficulties applying the biological species concept to asexually reproducing species and bacteria with horizontal gene transfer
• Binomial system for naming organisms

  A system for naming organisms using two names - the genus and the species
• Biological Species Concept


  • A group of organisms that interbreed to produce fertile offspring but are reproductively isolated from other groups
  • Doesn't apply to asexually reproducing species
  • Doesn't apply to extinct species
  • Over emphasizes gene flow and minimizes impact of natural selection
• Difficulties applying the biological species concept

  • To asexually reproducing species
  • To bacteria that have horizontal gene transfer
• Ecological Species Concept


  Defines a species in terms of its ecological niche: how species interacts with the abiotic and biotic factors of its environment
• Ecological Species Concept


  • Can include asexual and sexually reproducing species
  • Emphasizes the role of disruptive natural selection as organisms adapt to their environmental conditions
  • Niches are difficult to identify
• Speciation


  1. The process by which one species is split into two or more species

  2. Takes a very long time
• Gene pool


  The total of all alleles for a given gene in a population