What makes a phenotype

If the alleles are different Tt the genotype is heterozygous. It is actually rare that 1 gene determines 1 characteristic as in the case of PTC tasting a monogenic trait.

Most traits are complex and have genes that affect them at more than 1 locus polygenic. Your genes carry the instructions for the growth and development of your body.

However, your phenotype is influenced during embryonic development and throughout your life by environmental factors. Environmental factors are many and varied and include diet, climate, illness and stress.

Environmental factors that play a role include how dry your mouth is or how recently you have eaten. If environmental factors have a strong influence, the phenotypic plasticity is high. If genotype can be used to reliably predict phenotype, the phenotypic plasticity is low. It also includes traits that can only be observed using specialized equipment, such as different levels of gene expression. Genotype and phenotype are clearly discrete ideas, but they are often mentioned in tandem.

This is complicated, because our traits result from combinations of genes. There is rarely a trait that is linked to only one specific gene. Specifically, researchers want to know not only which genes are involved, but which variations within those genes are associated with a particular trait. For example, researchers have determined that the BRCA1 gene is linked to breast cancer risk in humans.

But simply having this gene does not tell us much, because only specific variations of BRCA1 have been associated with increased risk. Which genes put humans at risk of diabetes? Selection acts on phenotypes because differential reproduction and survivorship depend on phenotype.

If the phenotype affecting reproduction or survivorship is genetically based, then selection can winnow out genotypes indirectly by winnowing out phenotypes. How do we get from genotype to phenotype? Central dogma : DNA via transcription to RNA via translation to protein ; proteins can act to alter the patterns and timing of gene expression which can lead to cytodifferentiation where cells take on different states; cell communication can lead to pattern formation and morphogenesis and eventually we have an adult!

Genotype is also used to refer to the pair of alleles present at a single locus. With alleles 'A' and 'a' there are three possible genotypes AA, Aa and aa. With three alleles 1, 2, 3 there are six possible genotypes: 11, 12, 13, 22, 23, First we must appreciate that genes do not act in isolation.

The genome in which a genotype is found can affect the expression of that genotype, and the environment can affect the phenotype. An allele can be dominant over one allele but recessive to another allele.

Model of dominance from enzyme activity: no copies produce no phenotype, one copy produces x amount of product and two copies produces 2x then the alleles are additive and there is no dominance intermediate inheritance.

If one copy of the allele produces as much product or has as high a rate of flux as a homozygote then there is dominance. There are cases where the heterozygote is greater in phenotypic value than either homozygote: called overdominance. Single genes do not always work as simply as indicated by a dominance and recessive relationship.

And so it's an observable type of an organism, and it can refer to anything from a common trait, such as height or hair color, to presence or absence of a disease. Frequently, phenotypes are related and used--the term is used--to relate a difference in DNA sequence among individuals with a difference in trait, be it height or hair color, or disease, or what have you. But it's important to remember that phenotypes are equally, or even sometimes more greatly influenced by environmental effects than genetic effects.