What is the difference between polygenic inheritance and incomplete dominance

Polygenes show a great significance in evolution since they produce many different genotypes. The polygenic traits highly depend on external environmental factors.

The kernel color in wheat and corolla length in tobacco are examples of polygenic traits in plants. Most of the quantitative traits such as the height, weight, body shape, behavior, intelligence, eye color, skin color, and hair color of humans are controlled by polygenes. Sixteen different genes are involved in determining the amount of melanin produced in the iris of the eye, which ultimately produces the color of the eye.

Depending on the amount of melanin produced in the iris, different eye colors can be identified among humans such as black, brown, green, hazel, and blue. The hazel color eyes are shown in figure 2. Multiple Alleles: Multiple alleles refer to a series of three or more alternative forms of a gene.

Polygenic Traits: Polygenic trait is a trait that is controlled by a group of nonallelic genes. Multiple Alleles: Only two types of alleles are present in an individual; multiple alleles can be found within the population. Polygenic Traits: All polygenes can be found in the individual. Multiple Alleles: Only one gene consists of more than two alleles. Polygenic Traits: In polygenic traits, many genes control a single trait.

Multiple Alleles: Multiple alleles determine a trait by complete dominance or codominance. Polygenic Traits: Polygenic traits determine a trait by codominance or incomplete dominance. Multiple Alleles: Environmental factors have no influence in the determination of a trait by multiple alleles. Polygenic Traits: Environmental factors have a higher influence in the determination of a trait by polygenes. Multiple Alleles: Multiple alleles are located at the same loci of homologous chromosomes.

Polygenic Traits: The polygenes are located at different loci of non-homologous chromosomes. Multiple Alleles: Homologous crossing over does not occur between the loci of multiple alleles.

Polygenic Traits: Homologous crossing over can occur between the two alleles of each polygene. Multiple Alleles: Multiple alleles determine qualitative traits. It is determined by the amount of the brown color pigment melanin that a person has in the front part of the iris.

Black and dark brown eyes have more melanin than hazel or green eyes. Blue eyes have no melanin in the iris. Several other genes that determine eye color also influence skin color and hair color. Understanding that eye color is determined by a number of different genes, for this example, we will assume that it is determined by two genes.

In this case, a cross between two individuals with light brown eyes BbGg would produce several different phenotype possibilities.

In this example, the allele for black color B is dominant to the recessive blue color b for gene 1. For gene 2 , the dark hue G is dominant and produces a green color. The lighter hue g is recessive and produces a light color. This cross would result in five basic phenotypes and nine genotypes. Having all dominant alleles results in black eye color. The presence of at least two dominant alleles produces the black or brown color. The presence of one dominant allele produces the green color, while having no dominant alleles results in blue eye color.

Like eye color, skin color is an example of polygenic inheritance. This trait is determined by at least three genes and other genes are also thought to influence skin color. Skin color is determined by the amount of the dark color pigment melanin in the skin. The genes that determine skin color have two alleles each and are found on different chromosomes.

If we consider only the three genes that are known to influence skin color, each gene has one allele for dark skin color and one for light skin color. The allele for dark skin color D is dominant to the allele for light skin color d. Skin color is determined by the number of dark alleles a person has. Individuals who inherit no dark alleles will have very light skin color, while those that inherit only dark alleles will have very dark skin color.

Individuals who inherit different combinations of light and dark alleles will have phenotypes of varying skin shades. Those who inherit an even number of dark and light alleles will have a medium skin color. The shape and color of the flower, stem, pollen, size of a seed, yield, oil content, time to mature or reach flowering, etc. The kernel color of the wheat is controlled by the expression of the three independently assorted pairs of alleles.

The dark red wheat kernel is an expression of all dominant alleles, i. Further, in the F2 generation, during crossbreeding, there would be 1 white kernel plant while 63 red kernel plants with varying shades would be produced. The length of the corolla in the tobacco plant is an expression of the 5 genes. The variation in the length of the corolla in tobacco is due to polygenic inheritance. Polygenes are highly influenced by environmental factors. Basically, the genotype of an individual sets the range of the quantitative trait while the phenotype of the trait is eventually an outcome of the environmental factors.

Different environmental conditions regulate the gene function resulting in varying gene function. Accordingly, under different environmental conditions, the gene function may switch OFF or switch ON. Depending on the genotype involved, the norm of reaction can be classified as:.

Nature and nurture both affect phenotypic expression. Intelligence, depression, height, skin color, schizophrenia are some of the human characters that are affected by the environment.

A medical example of the effect of environmental factors on polygenic inheritance is the hereditary disorder phenylketonuria. The individual with homozygous alleles for the PKU disease lacks the enzyme that breaks down the amino acid, phenylalanine. In such patients, phenylalanine is retained in the body resulting in toxic buildup.

This toxic build-up eventually causes intellectual disability, seizures, and mood disorders. The treatment for this disorder is very simple, by keeping the patients on a specific diet. The dietary change helps to reduce or even alleviate the phenylketonuria disorder. Due to this, many countries screen newborns for their genetic constitution to identify phenylketonuria disorder. Polygenes are responsible for the population variance and have evolutionary significance.

These polygenic variations or changes polygenesis are responsible for the evolution of species. This is also known as the theory of polygeny for evolution. The variations are according to the specific requirement and needs of the individual or species. These are essentially responsible for adaptive changes. The polygenes are majorly applied or utilized by the plant breeders.

The genetic variability is stored in the form of polygenic complexes. Segregation and recombination of polygenic genes after interbreeding results in the release of hidden variability in a species. Humans are diploid creatures. This means that for every chromosome in the body, there is another one to match it.

However, there are organisms that have more than two sets of chromosomes. The condition is called polyploidy. Know more about this topic through this tutorial Read More. Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the different steps of the biological production of protein starting from the gene up to the process of secretion.

Also included are topics on DNA replication during interphase of the cell cycle, DNA mutation and repair mechanisms, gene pool, modification, and diseases Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Table of Contents. Biology definition: Polygenic inheritance is a non-Mendelian pattern of inheritance in which a particular trait is produced by the interaction of genes at many loci i.

Compare: monogenic inheritance.