Phenotype Information Resources
A phenotype is any
detectable characteristic of an organism determined by an interaction
between its genotype and environment. Danish botanist Wilhelm Johanssen drew
the distinction between an organism’s outward appearance (phenotype) and its
genetic traits (genotype) in 1909. The phenotype of an organism describes a
trait or characteristic that is measurable and is demonstrated only in a
subset of the whole populous (e.g. blue eyes or aggressiveness).
Some
phenotypes are entirely dictated by genes, others are partly determined by
genes but are influenced by environmental factors. Other phenotypes are
controlled entirely by extragenetic factors (language or cosmetically
altered physical characteristics). Countless phenotypes are determined by a
combination of multiple genes and various environmental factors. Because of
this, identifying a few alleles within an organism are not accurate
predictors of the organisms phenotype.
Phenotypes that can be observed
easily are utilised by Geneticists to hypothesise the organism’s genotype as
well as predicting the functioning of individual genes.
Phenotypic variation resulting from heritable genetic alterations is vital
for the natural selection process and ultimately evolution of the species.
Without this phenotypic variation, individuals would display the same
characteristics, and changes in phenotypic frequency would only occur
randomly. It can be said that genotype + environment = phenotype. A slightly
finer distinction would be to say that phenotype results from the
interaction of genotype + the environment + random variation.
The relationship between genes and the external sphere (known as
gene-environment interaction) describes phenotypic attributes that are
formed from a combination of environmental forces and the effects of genes.
The traditional nature-nurture debate espouses that variation within a
particular trait is due to either genetic influence of the life-experience
and situation of the organism. The accepted contemporary scientific
standpoint is that neither genes nor the environment account fully for
individual variation. Indeed, almost all traits show a degree of
gene-environment interaction.
Richard Dawkins proposes extending the definition of ‘phenotype’ to mean all
the effects a gene has that are external to the organism in which it resides
that may influence its chances of being replicated. Using Dawkins’ example,
the dam that a beaver builds should be considered a phenotype of beaver
genes in the same way as its incisor teeth are considered phenotypes
(expressions of the genes), termite mounds can be viewed in the same way.
The distinction between genotype and phenotype is that the genotype of an
organism represents its genetic makeup and is completely unique to that
individual organism. The word genotype can be understood as the entire
heritable information of that organism. Phenotype on the other hand,
represents the physical properties of the organism (height, physical
strength etc).
These characteristics directly affect the organism’s chances
of survival and of finding a suitable mate for reproduction to occur. The
inheritance of physical characteristics is secondary to the inheritance of
genes; therefore the genotype-phenotype distinction is vital to understand
the evolutionary path of a species. Similarly, providing an association
between genotype and phenotype is critical to understanding disease and for
the creation of models that can help to target critical pathways for such
diseases. |
