A phenotypic trait, or simply trait, is a distinct variant of a phenotypic characteristic of an organism that may be inherited, be environmentally determined or be a combination of the two. For example, eye color is a character or abstraction of an attribute, while blue, brown and hazel are traits.
Phenotypic trait is the element the descriptions of individuals and groups of living creatures. Individualized biological variability (biodiversity) of each species and populations of living beings, includes all the components of individual features or individuality and group identity in morphological and anatomical, biochemical and ethological, and every other way, from the level of molecules to living communities and a higher degrees of ecological integration.
Individuals and groups differ among themselves biologically, in practically endless succession of more or less visible elements of their descriptions, which are named as trait, feature, mark, nature, characteristics, character and others. Each of these components is a description of, say, the observational nature, i.e. selected part of our vision or measuring the actual condition of the individual body or group structure.
When it comes to individual variability, leg, leaf or capsule, e.g., are not traits, but authorities where we see a lot of features such as: total length, aspect ratio and size of the parts, the degree of pigmentation and schedule, strength and a huge number of other elements of its description. Similarly, the human eye is organ aparatus, and some of its features are: size, shape, color of the iris, a variety of functional (dis)abilities and so on. Blood is a liquid tissue, characterized by: the total amount in the body, the number of erythrocytes, leukocytes and platelets per unit volume, the concentration of sugar and other substances, group specificity of erythrocytes (blood), hemoglobin concentration, and many others.
While based on individual, group characteristics represent a new quality and a higher level of variability, and have different methods of observation and measurement.
In simple, it can be concluded that the overall biology is based on the study of individual characteristics, from the molecular level to the full body and its relationship to the environment. The nature of the variation of individual properties in the observed group can be described according to various criteria. Primary observation of individual traits is that some of them with all the members of the group studied occur in a compatible form or variant, the second - in two, and the rest in three or more mutually different varieties (phenotypes, variables, modalities, forms). On this basis, all the properties of the human body can be divided into monomorphic (red blood, for example.), dimorphic (Rh blood group system: Rh+ and Rh–) and polymorphic (series of variations of height, weight, surface, erytrocyte quantity in 1 ml of blod, and IQ, for example.); term and study the variability of the (course) refer only to the dimorphic and polymorphic features. According to the nature of intragroup variability (the type of variations), all features can be divided into two basic, very diverse categories:
- qualitative, and
- quantitative traits.
So, a phenotypic trait is an obvious and observable trait; it is the expression of genes in an observable way. An example of a phenotypic trait is hair color; there are underlying genes that control the hair color, which make up the genotype, but the actual hair color, the part we see, is the phenotype. The phenotype is the physical characteristics of the organism. The phenotype is controlled by the genetic make-up of the organism and the environmental pressures the organism is subject to.
A trait may be any single feature or quantifiable measurement of an organism. However, the most useful traits for genetic analysis are present in different forms in different individuals.
A visible trait is the final product of many molecular and biochemical processes. In most cases, information starts with DNA traveling to RNA and finally to protein (ultimately affecting organism structure and function). This is the central dogma of molecular biology as stated by Francis Crick.
This information flow may also be followed through the cell as it travels from the DNA in the nucleus, to the cytoplasm, to the ribosomes and the endoplasmic reticulum, and finally to the Golgi apparatus, which may package the final products for export outside the cell.
Genetic origin of traits in diploid organisms
The inheritable unit that may influence a trait is called a gene. A gene is a portion of a chromosome, which is a very long and compacted string of DNA and proteins. An important reference point along a chromosome is the centromere; the distance from a gene to the centromere is referred to as the gene's locus or map location.
Mendelian expression of genes in diploid organisms
Combinations of different alleles thus go on to generate different traits through the information flow charted above. For example, if the alleles on homologous chromosomes exhibit a "simple dominance" relationship, the trait of the "dominant" allele shows in the phenotype.
Gregor Mendel pioneered modern genetics. His most famous analyses were based on clear-cut traits with simple dominance. He determined that the heritable units, what we now call genes, occurred in pairs. His tool was statistics: long before the molecular model of DNA was introduced by James D. Watson and Francis Crick.
He is also known to have 'cheated' on his experiments, removing outliers and generally 'tidying' datasets - statistics, and repeating the experiments, shows that his results were just 'too perfect', a point first noted by RA Fisher, in 1936: http://www.cs.brown.edu/courses/csci1950-l/presentations/REVISED--AFCB%202007%20Course%20Fisher%20and%20Mendel.ppt
Biochemistry of dominance and extensions to expression of traits
Extended expression patterns seen in diploid organisms include facets of incomplete dominance, codominance, and multiple alleles. Incomplete dominance is the condition in which neither allele dominates the other in one heterozygote. Instead the phenotype is intermediate in heterozygotes. Thus you can tell that each allele is present in the heterozygote. Codominance refers to the allelic relationship that occurs when two alleles are both expressed in the heterozygote, and both phenotypes are seen simultaneously. Multiple alleles refers to the situation when there are more than 2 common alleles of a particular gene. Blood groups in humans is a classic example. The ABO blood group proteins are important in determining blood type in humans, and this is determined by different alleles of the one locus. 
Schizotypy is an example of a psychological phenotypic trait found in schizophrenia-spectrum disorders. Studies have shown that gender and age influences the expression of schizotypal traits. For instance, certain schizotypal traits may develop further during adolescence, whereas others stay the same during this period.
- Lawrence, Eleanor (2005) Henderson's Dictionary of Biology. Pearson, Prentice Hall. ISBN 0-13-127384-1
- *Campbell, Neil; Reece, Jane (March 2011) , "14", Biology (Sixth ed.), Benjamin Cummings
- Bailey, Regina. "What is incomplete dominance". About.com.
- McClean, Philip. "Variations to Mendel's First Law of Genetics".
- Unknown. "Multiple Alleles".
- Lawrence>Lawrence, Eleanor (2005) Henderson's Dictionary of Biology. Pearson, Prentice Hall. ISBN 0-13-127384-1
- Campbell, Neil; Reece, Jane (March 2011) , "14", Biology (Sixth ed.), Benjamin Cummings