Quantitative traits vary in characteristics and are influenced by two or more genes and environmental factors. They are often continuous and difficult to predict, and are documented using numbers and percentages. Polygenic inheritance and quantitative trait locus are involved in their formation, and they appear in nearly all organisms. Examples include height, intelligence quotient, and blood pressure in humans, and crop yield and disease resistance in plants.
In genetics, a quantitative trait is a trait that varies in its characteristics and expressions. Two or more genes, along with environmental interactions, are usually responsible for maximal expression. These traits are described in numbers and can vary in degrees. Most quantitative traits are continuous and often do not fall into any distinct category. The study of the inheritance of such traits is called “Quantitative Genetics” and such phenotypes in humans include – but are not limited to – height, intelligence quotient (IQ), and blood pressure.
When scientists know a genotype or the internal genetic code for a specific trait, they can predict the resulting phenotypes or external characteristics of that trait. These are referred to as discontinuous sections and are assigned discrete classes. Not all traits, however, neatly fit into a discrete classification, but are instead continuous and difficult to predict. Such types of traits are called quantitative traits because they are usually recorded as numerical distributions.
Polygenic inheritance is the term used by scientists to describe the formation of a quantitative trait. Genes that influence the value of quantitative traits are referred to as quantitative trait locus (QTL). Quantitative trait formation involves two or more genes that contribute to a phenotypic trait and often also involves interaction with the environment. Height in humans, for example, involves a number of genes; however, maximum gene expression is influenced by environmental factors, such as available nutrition. Rather than following a specific pattern, the strokes vary along a continuous gradient which is often illustrated on a bell curve.
Numbers and percentages are the primary methods for documenting quantitative traits. The numerical values of quantitative traits are often ordered from highest to lowest and represent a continuous order rather than a specified count along a continuous gradient. Quantitative trait values often differ only in small, arbitrary amounts rather than fixed amounts. Thus, most scientists assume continuous data rather than specific values or counts when documenting quantitative traits. Scientists attempt to predict the variance of a quantitative trait by finding the mean of distribution and plotting diffusion on a bell curve.
Quantitative trait expressions appear in nearly all organisms, often particularly in plant and animal life. In plants, examples include crop yield, color distribution, and disease resistance. In animals and people, weight, height, learning ability, and even blood pressure are expressed as a quantitative trait.
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