Genetics provides one of biology’s unifying principles: all organisms use genetic systems that have a number of features in common.
The complete set of genetic instructions for any organism is its genome, and all genomes are encoded in nucleic acids – either DNA or RNA. The coding system for genomic information is also common to all life: genetic instructions are in the same format and, with rare exceptions, the code words are identical. Likewise, the process by which genetic information is copied and decoded is remarkably similar for all forms of life. These common features suggest that all life on Earth evolved from the same primordial ancestor, which arose between 3.5 billion and 4 billion years ago.
Life’s diversity and adaptations are productions of evolution, which is simply genetic change over time. Genetic variation is therefore the foundation of all evolutionary change and is ultimately the basis of all life as we know it.
A few species have emerged as model genetic organisms – organisms with characteristics that make them particularly useful for genetic analysis and about which a tremendous amount of genetic information has accumulated. Six model organisms that have been the subject of intensive genetic study are Drosophila melanogaster, a species of fruit fly; Escherichia coli, a bacterium; Caenorhabditis elegans, a nematode (roundworm); Arabidopsis thaliana; the thale-cress plant; Mus musculus, the house mouse; and Saccharomyces cerevisiae, baker’s yeast.
The following are some fundamental genetic principles.
- Cells are of two basic types: eukaryotic and prokaryotic.
- The gene is the fundamental unit of heredity.
- Genes come in multiple forms called alleles.
- Genes confer phenotypes.
- Genetic information is carried in DNA and RNA.
- Genes are located on chromosomes.
- Chromosomes separate through the processes of mitosis and meiosis.
- Genetic information is transferred from DNA to RNA to protein.
- Mutations are permanent changes in genetic information that can be passed from cell to cell or from parent to offspring.
- May traits are affected by multiple factors.
- Evolution is genetic change.
—August 2020
Lance Jones 