The genotype/phenotype connection
What role do genes play in development? How does your genotype contribute to your phenotype? Or more explicitly, how do genes work together to produce RNA 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 Genetics Otago, who considers it one of the most important questions in biology.
Phenotype and genotype
The genotype of an organism is defined as the sum of all its genes. The phenotype of an organism is the observable physical or biochemical characteristics of an organism, determined by both genetic make-up and environmental influences.
The Human Genome Project 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.
Researching the link between genotype and phenotype
Professor Peter Dearden, from the University of Otago, is interested in how genotype makes phenotype. In this video, he talks about his laboratory’s research where they manipulate individual genes and observe any resulting changes in phenotype.
Jargon alert
Genotype: The genetic information, or DNA sequence, of an individual organism
Phenotype: The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.
Using insect models
Evolution 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 organism often allow scientists to gain a better understanding of human development and disease. 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 gene 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 protein) 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 embryo 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 interference, 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 species 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 evolved 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 Prize winner Sir Paul Nurse discusses how the Human Genome Project has impacted on scientific research.
The Human Genome Project
Why was the Human Genome Project so important, and where do we go to next? Nobel prize winner, Sir Paul Nurse, explains.
What impact is the Human Genome Project having on science? Has it lived up to its hype?
Useful links
Visit the National Human Genome Research Institute website to learn more about comparative genomics and model organisms.
See the Otago Biochemistry: Resources for high school students.
