model

• Species considered model organisms are those with well-characterized genetics and can be manipulated experimentally
• Caenorhabditis elegans and Mus musculus were the first generation organisms used as genetic models due to their well-characterized genetics and experimentation
• Bacteria, specifically Escherichia coli, have been used for recombinant DNA technology and associating specific diseases to individual genomes
• Model Organisms

  • Bacteria
  • Yeast
  • Arabidopsis thaliana (Mustard plant)
  • Caenorhabditis elegans (Round worm)
  • Drosophila melanogaster (Fruit fly)
  • Danio rerio (Zebra fish)
  • Chick Embryo
  • Mouse (Mus musculus)
• Bacteria have been proven to be a useful model system to investigate protein structure and function, with knowledge gained often applied to homologous proteins in more complex organisms
• Typical Characteristics of Model Organisms

  • Small adult size
  • Rapid development with short life cycles
  • Can be bred in large numbers
  • Readily available and inexpensive maintenance
  • Similar genes or similar-sized genomes to humans
  • Tractability to experimental methodology
  • Genetic analysis is fairly straightforward
• Human Genome Project (2003) involved sequencing the genomes of five model organisms: Bacteria (Escherichia coli), Yeast (Saccharomyces cerevisiae), Fruit fly, Caenorhabditis elegans, Mus musculus
• The rediscovery of Mendel’s work in the 1900s using a wide range of organisms confirmed the principles of inheritance
• Escherichia coli is an excellent model organism for geneticists due to its small size, easy growth in the laboratory, and short generation time
• Model Organism


  A non-human species extensively studied to understand basic biological phenomena, with discoveries extrapolated to other species, including humans
• E. coli


  • Small and takes up very little laboratory space
  • Easy to grow in the laboratory without the need for expensive supplies and equipment
  • Has very short generation or doubling time in their ideal growth conditions – as low as 15-20 mins
  • Already has its genome sequence and has been studied extensively for many decades now, providing geneticists a wealth of information to use for experimental design and interpretation of results
  • Bacteria share many basic biological processes with higher level organisms
  • Easily manipulated genetically
  • Haploid with only one copy of its chromosome
  • Scientists do not have difficulty in observing the effects of a genetic manipulation because they don’t need to worry about the issues of dominant vs recessive traits
• Caenorhabditis elegans


  • One of the best characterized multicellular animals at the level of genomics, genetics, embryology
  • Genome fully sequenced
  • Unique in that it can be grown and genetically manipulated with the speed and ease of a micro-organism while offering the features of a real animal
  • Has a full set of organ systems, complex sensory systems, shows coordinated behavior, and it is possible to trace the lineage of every one of its approximately 1000 constituent cells
  • Either male only or hermaphrodite
  • Each worm is made up of about 1000 somatic cells, 1/3 are nerve cells, germ cells about the same number as the nerve cells
  • Can be grown cheaply and in large numbers on plates containing bacteria
  • Produces over 1000 eggs everyday
  • Life cycle: 2 weeks
  • Very small organism – convenient to keep in t
• Yeast as a Model Organism

  • Eukaryotic system
  • Yeast cells have a nucleus that contains DNA packaged inside a chromosome
  • Signaling molecules and cell cycle are nearly similar
  • Good model system to understand many human diseases including cancer
  • Ease of genetic manipulation allows its use for analyzing and functionally dissecting gene products from other eukaryotes
  • Baker’s yeast or Saccharomyces cerevisiae is known to be among the best studied experimental organisms, commonly used in the bread-making industry
  • Genes with the most similarities shared between humans and yeast: MSH2 – MutS homolog 2, MLH1 - MutL homolog 1, involved in Hereditary non-polyposis colorectal cancer in Humans
• Life cycle of Drosophila is 8-14 days and depending on the environmental temperature, several generations can be observed in just a matter of months
• Transfer of human mutant disease genes to Drosophila using recombinant DNA technology is used to study human mutant genes
• 1/3 of somatic cells are nerve cells
• Transgenic organisms have their genome modified by the introduction of external DNA sequence into their germ line
• Fruit fly (Drosophila melanogaster)

  • Easy-to-manipulate genetic system and can be used to study development, physiology, and behavior
  • Biological complexity comparable to that of a mammal
  • Many organ systems in mammals have well-conserved homologues in Drosophila
  • Has provided insights into forms of cancer, neurodegenerative diseases, behavior, immunity, aging, multigenic inheritance, and development
• C. elegans mutants provide models for many human diseases including neurological disorders, congenital heart disease, kidney diseases, studying cell death (apoptosis), and can hold the key for counteracting the effects of aging for humans, as well as providing clues for cancer, diabetes, and other diseases
• Research areas using C. elegans

  • Developmental and Cell biology
  • Neurobiology
  • Aging
  • Human disease studies
• C. elegans can be grown cheaply and in large numbers on plates containing bacteria
• Mutant genes in Drosophila melanogaster have been identified that produce phenotypes with abnormalities of the nervous system, including abnormalities of brain structure, adult onset degeneration, and visual defects such as retinal degeneration (retinitis pigmentosa)
• Alzheimer's disease is a progressive neurologic disorder that causes the brain to shrink (atrophy) and brain cells to die
• C. elegans produce over 1000 eggs everyday
• C. elegans life cycle is 2 weeks
• Germ cells are about the same in number as nerve cells
• Fruit fly (Drosophila melanogaster) is a versatile model organism extensively used for biomedical research
• Gene transfer approach is used to study human neurodegenerative disorders including Huntington Disease, Machado-Joseph, Myotonic, and Alzheimer's disease
• Study of mutations in Drosophila melanogaster is helping to dissect retinitis pigmentosa and identify the function of the genes involved
• Zebrafish (Danio rerio) has small size, short life cycle, ease of culture, and ability to readily produce mutations relevant to human health and disease
• Zebra fish (Danio rerio)

  • Small size, short life cycle, ease of culture, ability to produce mutations relevant to human health and disease
  • Embryonic development can be seen through its transparent egg and closely resembles that of higher vertebrates
  • Shared features with humans include blood, kidney, and optical systems
  • Genome is half the size of the mouse and human genomes, valuable in identification of key vertebrate genes
  • Used to study vertebrate development
• Mouse (Mus musculus)

  • Closest mammalian model organism to humans
  • Useful in development, genetic, and immunology studies
  • Cost-effective, multiplies quickly, better than flies or worms in studying complex biological systems found in humans
  • Naturally develop diseases that affect systems including cancer and diabetes
• Feeding schedule for Zebra fish

  Change their food regularly every 10-14 days if the temperature is 25C or every 5-6 weeks at 18C
• Chick Embryo (Gallus gallus domesticus)


  • Provides an excellent model system for studying the development of higher vertebrates
  • Can be used to observe GFP (Green Fluorescent Protein) or Roslin Green (Cytoplasmic GFP)
  • Valuable for research as most of their development takes place within an egg that is incubated outside of the mother
  • Ideal tool for studying the formation and patterning of the brain, neural tube, somite, and heart primordia
• Arabidopsis thaliana (Thale cress)


  • Small plant with white flowers, often considered to be a weed where it is found
• Prof. Pamela Sengson, RMT, MPH: '[CYTO311] TRANS: MODEL ORGANISMS'
• Knockout mouse


  • Laboratory mouse in which one or more genes has been turned off
  • Used to study what happens in an organism when a particular gene is absent
  • Provides information about how the knockout gene normally functions including biochemical, developmental, physical, and behavioral roles
  • Used to discover functions of human genes and study human diseases
• Arabidopsis thaliana is a small flowering plant with a small genome relative to other plants and is easily grown under laboratory conditions
• There are 2 types of gene mapping: Genetic Mapping (Linkage Map/Recombination map) - using linkage analysis to determine the relative position between two genes on a chromosome, and Physical Mapping - using all available techniques or information to determine the absolute position of a gene on a chromosome
• Arabidopsis thaliana


  • Amenable to some genetics particularly generation of transgenics
  • Allows insight into numerous features of plant biology, including those of significant value to agriculture, energy, environment, and human health