Phenotype: Definition, Characteristic, and Examples
Phenotype Definition
The word “phenotype” is defined in biology as an organism’s observable and quantifiable traits as a result of the interplay between the organism’s genes, environmental variables, and random variation. The phenotype of an organism includes not only observable traits like appearance, but also molecules and structures like RNA and proteins generated as coded by genes; this is referred to as “molecular phenotype.”
What is Phenotype?
The visible features of an organism as a multifactorial result of hereditary traits and environmental effects are referred to as phenotype. The morphological, biochemical, physiological, and behavioural characteristics of an organism make up its phenotype. As a consequence of the expression of an organism’s genes, as well as the impact of environmental variables and random variation, the phenotype is the entire set of traits shown by that organism. The following relationship has typically been used to illustrate the interplay between these factors: genotype + environment + random variation phenotype.
The relationship between phenotype and genotype is depicted in this graphic (Punnett square). The B and b genes are responsible for the pea plant’s petal colour. The dominant characteristic is a purple-petalled bloom, which is the result of the B gene. The recessive characteristic is the b gene. Three children with the purple-flower trait (BB and Bb) and one offspring with the white-flower trait will result from a test cross between two plants that are heterozygous (Bb) for the purple petal colour trait (bb). The phenotypic ratio in this instance is 3:1.
Phenotype Etymology
Phenotype is derived from the Latin phaeno-, which comes from the Greek phaino-, which means “shining,” from phanein, which means “to shine,” “to appear,” or “to show,” and -type from “typos.” Genotype is a similar term. The term phenotypic is a descriptive term that refers to, describes, or refers to the phenotype of a certain organism.
Trait vs Phenotype
A trait is a feature of the phenotypic of an organism. To differentiate one characteristic from another under the more-inclusive word, phenotype, the trait is sometimes referred to as a phenotypic trait in genetics. An organism’s phenotype is made up of several characteristics. Traits can be inherited (genetically determined), acquired (as a consequence of environmental factors), or a combination of both. For example, hair colour is a personality feature that might be black, blonde, ginger, or brunette.
Phenotype vs Genotype
Genotype and phenotype are words used in genetics to describe an organism’s appearance, function, and behaviour. A genotype is a collection of genes that, when expressed, determine an organism’s feature or attribute. To put it another way, the genotype is the genetic component of the phenotype.
DNA sequences are made up of genes. They come in pairs in humans and other animals, one from the male parent and the other from the female parent. Alleles are genetic pairings that share the same loci on the chromosomes and control the same characteristic.
A pair of genes (or alleles) for a certain trait often consists of two genes, one dominant and the other recessive. The dominant allele will show up as a characteristic, whereas the recessive allele will not. There are three genotypes that may be identified by annotating the dominant allele with A and the recessive allele with a:
(1) AA, homozygous dominant allele,
(2) Aa, heterozygous dominant, and
(3) aa, homozygous recessive.
An organism’s genotype is a key factor in determining its phenotype. A pair of genes (or alleles) for a specific trait is usually made up of two, one dominant and the other recessive. The dominant allele will manifest itself as a characteristic, while the recessive allele will not. The dominant allele is labelled with A, and the recessive allele is labelled with an in three possible genotypes:
(1) AA represents the homozygous dominant allele,
(2) Aa represents the heterozygous dominant allele, and
(3) aa represents the homozygous recessive allele.
An organism’s genotype is a significant determinant of its phenotype. Take, for example, a pair of alleles (or genes) that defines a certain characteristic, one of which is dominant (A) and the other recessive (B) (a). The dominant allele (A) will be expressed and form part of the organism’s phenotype, whereas the recessive allele (a) will be muted.
When a characteristic is inherited according to Mendelian principles, the A will appear as a trait, but the a will not. As a result, an organism’s phenotype must incorporate the characteristics of all expressed genes. Many observable characteristics in humans, however, are more complicated than those that follow the Mendelian pattern. In the case of polygenic inheritance, complex characteristics such as height and skin colour are caused by the interactions of many alleles.
Expression
Genetic factors, environmental effects, and random genetic variants all contribute to the phenotypic. The characteristic is defined as homozygous when the pair of alleles defining a specific trait comprises identical genes, e.g. AA or aa. The characteristic is defined as heterozygous when the allelic makeup comprises of various genes, such as Aa. The presence of the dominant allele, such as AA or Aa, causes the characteristic (A) to manifest, whereas the lack of the dominant allele, such as aa, causes the opposite trait to appear (a). This is an example of full dominance, and it is inherited in the Mendelian manner.
The expression of a characteristic will not follow the Mendelian pattern in situations of codominance, imperfect dominance, or polygenic inheritance. Because both alleles in a pair are dominant in codominance, the alleles of a gene pair in a heterozygote will be completely expressed (e.g. AB). The resultant characteristic under incomplete dominance will be a mix of the impacts of the two alleles. Because the dominant allele will only be partly expressed, this is the case. As a result, the heterozygous offspring will have a phenotype that is halfway between the parents’ phenotypes.
Aside from genetic interactions, an organism’s phenotype is influenced by the environment as well as random (genetic) variations. Environmental variables may have an impact on an organism’s appearance. A light-colored skin that is continually exposed to the sun’s rays, for example, will darken as a result of increased melanin synthesis. Random variation, on the other hand, might modify a physical feature or, at the very least, an organism’s fitness. Gene changes are critical since they are what drives evolution and natural selection. Individual phenotypes are explained in part by genotypes, environmental influences, and genetic variants.
Extreme Phenotype
When the alleles of both parents join together, the outcome is a hybrid with a phenotype that is larger or higher than the phenotypes of both parents. Its transgressive phenotype might be advantageous or harmful, depending on how it impacts the offspring’s total fitness. Transgressive segregation is the development of extreme phenotypes. The child of a cross between Helianthus annuus and Helianthus petiolaris is an example of a hybrid with an extreme phenotype. Transgressive hybrids were created from the two sunflower species. In contrast to their parents, hybrids can survive in environments where their parents can not. Sand dunes and salt marshes are not a problem for them.
Recombinant Phenotype
Meiosis is an essential biological process that leads to an increased variety of organism phenotypes. The homologous chromosomes come together during the metaphase of meiosis, in particular, to swap genes via homologous recombination. The four daughter cells will contain chromosomes that are different from one another when the homologous chromosomes approach the conclusion of meiosis (telophase II). Some of them will develop into gametes with recombinant genes.
When such a gamete is fertilised with a wild type, for example, it will produce an offspring with a recombinant phenotype, which is distinct from its parents’ phenotypes. A test cross between two characteristics (for example, a blue-bodied, normal-winged fly father and a black-bodied, vestigial-winged fly parent) can aid in the identification of recombinant phenotypes. Recombinants are children with traits that differ from their parents (for example, a blue-bodied, vestigial-winged fly or a black-bodied, normal-winged fly).
Phenotypic Ratio
Another technique for identifying all potential allelic pairings in a test cross is a Punnett square. It can forecast the offspring’s genotypes and traits. It’s a grid and letter graphic that represents alleles. A dominant trait or genotype is denoted by an uppercase letter (e.g. A), while a recessive trait or genotype is denoted by a lowercase letter (e.g. a). The phenotypic ratio (as well as the genotypic ratio) may be calculated using the Punnett square. A phenotypic ratio is a proportion that may be anticipated based on the results of a test cross. It can be determined based on the phenotypes of the offspring, or the frequency with which distinct characteristics or trait combinations are manifested in the offspring.
For example, based on the four possible phenotypes: AaBb (blue, normal-winged fly), aaBb (black, normal-winged fly), Aabb (blue, vestigial-winged fly), and aabb (blue, vestigial-winged fly), the expected phenotypic ratio of an AaBb x aabb dihybrid cross (i.e. a cross that deals with (black, vestigial-winged fly).
Phenotype Example
As previously stated, an organism’s phenotype refers to the many qualities that it contains. Blue eye trait (for eye colour character), brown skin trait (for skin colour character), long-tail trait (for tail character), five-petalled trait (for flower character), and so on are examples of traits. Another example of a phenotype is behaviour. Individuals with mental retardation, for example, have behavioural and cognitive characteristics that constitute behavioural phenotypes.
Phenotype Citations
- Structural properties of genotype-phenotype maps. J R Soc Interface . 2017 Jul;14(132):20170275.
- Bridging the genotype-phenotype gap: what does it take? J Physiol . 2013 Apr 15;591(8):2055-66.
- Natural History and Genotype-Phenotype Correlations in RDH12-Associated Retinal Degeneration. Adv Exp Med Biol . 2019;1185:209-213.Â
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