Single Gene Inheritance

The genetic approach to understanding any biological property is to find the subset of genes in the genome that influence that property, a process sometimes referred to as gene discovery. After these genes have been identified, their cellular functions can be elucidated through further research.

There are several different types of analytical approaches to gene discovery, but one widely used method relies on the detection of single-gene inheritance patterns.

All of genetics, in one aspect or another, is based on heritable variants. The basic approach of genetics is to compare and contrast the properties of variants, and from these comparisons make deductions about genetic function. It is similar to the way in which you could make inferences about how an unfamiliar machine works by changing the composition or positions of the working parts, or even by removing parts one at a time. Each variant represents a “tweak” of the biological machine, from which its function can be deduced.

In genetics, the most common form of any property of an organism is called the wild type, that which is found “in the wild,” or in nature. The heritable variants observed in an organism that differs from the wild type are mutants, individual organisms having some abnormal form of a property.  The alternative forms of the property are called phenotypes. In this analysis we distinguish a wild-type phenotype and a mutant phenotype.

Compared to wild type, mutants are rare. We know that they arise from wild types by a process called mutation, which results in a heritable change in the DNA of a gene. The changed form of the gene is also called a mutation. Mutations are not always detrimental to an organism; sometimes they can be advantageous, but most often they have no observable effect. A great deal is known about the mechanisms of mutation, but generally it can be said that they arise from mistakes in cellular processing of DNA.

Most natural populations also show polymorphisms, defined as the coexistence of two or more reasonably common phenotypes of a biological property such as the occurrence of both red- and orange-fruited plants in a population of wild raspberries. Genetic analysis can (and does) use polymorphisms, but polymorphisms
have the disadvantage that they generally do not involve the specific property of interest to the researcher. Mutants are much more useful because they allow the researcher to zero in on any property.

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