Aphenotypic trait,[1][2] simplytrait, orcharacter state[3][4] is a distinct variant of aphenotypic characteristic of anorganism; it may be eitherinherited or determined environmentally, but typically occurs as a combination of the two.[5] For example, havingeye color is acharacter of an organism, while blue, brown and hazel versions of eye color aretraits. The termtrait is generally used ingenetics, often to describe the phenotypic expression of different combinations ofalleles in different individual organisms within a singlepopulation, such as the famous purple vs. white flower coloration inGregor Mendel's pea plants. By contrast, insystematics, the termcharacter state is employed to describe features that represent fixed diagnostic differences amongtaxa, such as the absence of tails ingreat apes, relative to otherprimate groups.[6]
Aphenotypic trait is an obvious, observable, and measurable characteristic of an organism; it is the expression of genes in an observable way. An example of a phenotypic trait is a specific hair color or eye color. Underlying genes, that make up thegenotype, determine the hair color, but the hair color observed is the phenotype.
The phenotype is dependent on the genetic make-up of the organism, but is also influenced by the environmental conditions that the organism was subjected to during itsontogenetic development,[7] including variousepigenetic processes.
Regardless of the degree of influence of genotype versus environment, the phenotype encompasses all of the characteristics of an organism, including traits at multiplelevels of biological organization, ranging frombehavior andevolutionary history of life traits (e.g., litter size), through morphology (e.g., body height and composition), physiology (e.g., blood pressure), cellular characteristics (e.g., membrane lipid composition, mitochondrial densities), components ofbiochemical pathways, and evenmessenger RNA.[citation needed]
Different phenotypic traits are caused by different forms ofgenes, oralleles, which arise bymutation in a single individual and are passed on to successive generations.[8]
Thebiochemistry of the intermediate proteins determines how they interact in the cell. Therefore, biochemistrypredicts how different combinations of alleles will produce varying traits.[citation needed]
Extended expression patterns seen in diploid organisms include facets ofincomplete dominance,codominance, andmultiple 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.[9] Codominance refers to the allelic relationship that occurs when two alleles are both expressed in the heterozygote, and both phenotypes are seen simultaneously.[10] 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. TheABO blood group proteins are important indetermining blood type in humans, and this is determined by different alleles of the one locus.[11]
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.[12] For instance, certain schizotypal traits may develop further during adolescence, whereas others stay the same during this period.[12]
