What role do genes1 play in development? How does your genotype2 contribute to your phenotype3? Or more explicitly, how do genes work together to produce RNA4 that codes for proteins that make up your cells, tissues and organs, leading to your phenotype (the physical expression of your genes)?
Honey bee embryo
Queen bee ovariole imaged on a confocal microscope. This type of image helps scientists understand how the ovary works in a bee and how it responds to environmental signals that repress or activate it. The red staining is DNA. The green is a stain for cortical actin, which marks the boundaries of cells in most cases. The section with the prominent red-stained nuclei is the nurse cell cluster. These cells are making RNA and protein and transporting them into the adjacent cells.
This question intrigues Professor Peter Dearden, Director of Genetics5 Otago, who considers it one of the most important questions in biology6.
Phenotype and genotype
The genotype of an organism7 is defined as the sum of all its genes. The phenotype of an organism is the observable physical or biochemical8 characteristics of an organism, determined by both genetic9 make-up and environmental influences.
The Human Genome Project10 has raised the profile of genome research – the genomes of over 1,000 organisms have now been sequenced. This has provided a lot of information about genes and genomes and made it possible to investigate the relationship between genotype and phenotype.
Researchers are finding that there are more similarities between genomes of different organisms than there are differences and that many of the phenotypic differences between organisms are due to differences in the way their genes are turned on and off, not due to what genes they have.
Using insect models
Evolution11 and development are particular themes for the research carried out by Peter and his colleagues. Current work focuses on investigating how the processes that occur during the development of an organism change over evolutionary time scales to give different forms of the same organism. One of the key aspects of this research is investigating how an organism’s genotype results in a particular phenotype.
To carry out this research, Peter and his colleagues work with a number of model organisms, including honey bees (Apis mellifera) and fruit flies (Drosophila melanogaster).
Nature of science
Animal and cell-based models are often needed to explore the complexity of human development and genetics. The biological pathways between animal models and humans are not identical, but discoveries made using a model organism12 often allow scientists to gain a better understanding of human development and disease13. The particular line of scientific inquiry will inform the animal model the scientist chooses.
Turning genes on or off
Peter’s approach to understand the role of genes in the development process involves switching genes on and off to see how the phenotype is affected. However, this type of research is very challenging!
In the 20th century, D. melanogaster was a popular insect model for genetic research projects. Turning a gene14 on or off in a fruit fly is a well defined technique that allows scientists to determine the role of a gene in an organism’s development. When a gene is turned off by chemical or physical means, its gene product (a protein15) will not be produced, and the impact of the lack of that protein on development can be seen. However, turning a gene on or off in the embryo16 of a bee is more difficult.
Peter’s recent work has focused on developing lab techniques to turn genes off in honey bees. By modifying a technique called RNA interference17, they have discovered a way to turn genes off in a honey bee embryo. They are now able to go ahead with a new research phase where they can manipulate individual genes and see what happens. This will enable them to compare the roles that different genes play in the development of the fruit fly compared with the honey bee.
Same gene, different result
Peter and his colleagues have found that D. melanogaster and A. mellifera have almost exactly the same genes, but in many instances, the way that they work is completely different. For example, both species18 have a gene called caudal. In D. melanogaster, it turns on a gene called giant, and in A. mellifera, it turns off giant. Its role has evolved19 from turning a gene on to turning a gene off.
This is not a unique finding in itself. What their research is illustrating is that it’s the way that the genes influence each other that evolves, not the genes themselves. Although this research is still developing, Peter hopes their work will add significantly to the current understanding of development and evolution.
Watch this video clip below in which Nobel Prize20 winner Sir Paul Nurse discusses how the Human Genome Project has impacted on scientific research.
Useful links
Visit the National Human Genome Research Institute website to learn more about comparative genomics21 and model organisms.
See the Otago Biochemistry: Resources for high school students.
- genes: A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.
- genotype: (Noun) The genetic information, or DNA sequence, of an individual organism. (Verb) To identify DNA sequence information.
- phenotype: The observable physical or biochemical characteristics of an organism, determined by both genetic make-up and environmental influences.
- RNA: A molecule generated in cells by transcription and required for the synthesis of proteins. RNA (Ribonucleic acid) is made up of a large number of nucleotides to form a long single strand. A chemical code for genetic information.
- genetics: The study of heredity and variation in living organisms.
- biology: The science of living things.
- organism: A living thing.
- biochemical: Any organic compound involved in living processes, for example, a protein, carbohydrate or lipid.
- genetic: Of, relating to, or determined by genes.
- Human Genome Project: An international project to identify all the genes in human DNA and to determine the sequence of the 3 billion nucleotides that make up human DNA.
- evolution: In biology, the change in the genetic material and/or the behaviour of a population of organisms over time.
- model organism: A non-human species used by scientists to better understand particular biological research questions.
- diseases: 1. An abnormal condition of an organism that impairs bodily functions. 2. In plants, an abnormal condition that interferes with vital physiological processes.
- genes: A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.
- protein: Any of a large class of complex compounds that are essential for life. Proteins play a central role in biological processes and form the basis of living tissues. They have distinct and varied three-dimensional structures. Enzymes, antibodies and haemoglobin are examples of proteins.
- embryo: The product of a fertilised egg, from the zygote until the foetal stage. The undeveloped plant that forms when the ovule is fertilised.
- RNA interference (RNAi): The process when a double-stranded RNA molecule prevents a messenger RNA (mRNA) molecule from being translated into a protein. Also called RNA silencing or RNA inactivation.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- evolve: To develop gradually. Changes in successive generations over long periods of time.
- Nobel Prize: An annual, prestigious international award for achievement in physics, chemistry, physiology or medicine, literature and peace.
- genomics: A discipline in genetics that applies DNA sequencing methods and bioinformatics to sequence, assemble and analyse the function and structure of genomes.
