3.2: Model Organisms Facilitate Genetic Advances
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Many of the great advances in genetics were made using species that are not especially important from a medical, economic, or even ecological perspective. Geneticists, from Mendel onwards, have sought the best organisms for their experiments. Today, a small number of species are widely used as model organisms in genetics (Fig 1.17). All of these species have specific characteristics that make large number of them easy to grow and analyze in laboratories: (1) they are small, (2) fast growing with a short generation time, (3) produce lots of progeny from matings that can be easily controlled, (4) have small genomes (small C-value), and (5) are diploid (i.e. chromosomes are present in pairs).
The most commonly used model organism are:
- The prokaryote bacterium, Escherichia coli, is the simplest genetic model organism and is often used to clone DNA sequences from other model species.
- Yeast (Saccharomyces cerevisiae) is a good general model for the basic functions of eukaryotic cells.
- The roundworm, Caenorhabditis elegans is a useful model for the development of multicellular organisms, in part because it is transparent throughout its life cycle, and its cells undergo a well-characterized series of divisions to produce the adult body.
- The fruit fly (Drosophila melanogaster) has been studied longer, and probably in more detail, than any of the other genetic model organisms still in use, and is a useful model for studying development as well as physiology and even behavior.
- The mouse (Mus musculus) is the model organism most closely related to humans, however there are some practical difficulties working with mice, such as cost, slow reproductive time, and ethical considerations.
- The zebrafish (Danio rerio) has more recently been developed by researchers as a genetic model for vertebrates.Unlike mice, zebrafish embryos develop quickly and externally to their mothers, and are transparent, making it easier to study the development of internal structures and organs.
- Finally, a small weed, Arabidopsis thaliana, is the most widely studied plant genetic model organism. This provides knowledge that can be applied to other plant species, such as wheat, rice, and corn.