What is the difference between monogenic and polygenic inheritance

Human phenotypes or human physical traits such as hair color, height, skin color, blood pressure, intelligence, autism, and longevity are some of the examples of polygenic inheritance. These traits exhibit multiple and continuous variations of the phenotype. Polygenic inheritance is controlled by two types of alleles or genes, namely :.

These alleles are sometimes referred to as effective and non-effective alleles , respectively. The pioneering work to understand the quantitative characters in terms of Mendelian genetics was carried out by Sir Ronald Aylmer R. Fisher in As we are aware that polygenic inheritance is a quantitative inheritance. Hence, it becomes important to understand the approaches or basis to differentiate between quantitative and qualitative inheritance.

Oligogenic traits are controlled by a limited number of genes whereas polygenic traits are controlled by a number of genes. The difference between polygenic trait and oligogenic traits are enlisted in the table below. Variance is used to segregate the polygenic variation or variability present in a genetic population. The variation in polygenic inheritance is of three types.

They are:. The color of the skin is polygenic inheritance. It is controlled by around 60 loci. To understand the inheritance pattern of skin color let us consider an example of pair of three different alleles present at unlinked loci represented as A and a , B and b , C and c. The alleles responsible for dark color skin are represented by letters where capital letters represent those that are incompletely dominant alleles.

Further, in the F2 generation of two triple heterozygotes parents — AaBbCc x AaBbCc — will produce varying skin colors ranging from very dark to very light, the ratio of which would range in see Figure 1. The skin color of an individual is due to the presence of melanin in the skin. Conversely, a light skin color aabbcc would have the least or a negligible amount of melanin in the skin. Human height is a polygenic trait that is controlled by three genes that have six alleles.

So, a tall person would have all dominant alleles whereas a short person will have the most number of recessive alleles. Like all the polygenic inheritance patterns, human height inheritance also follows a normal distribution curve wherein the extreme ends of the curve represent either extremely short or tall people, while the middle portion of the curve represents the population with average height see Figure 2.

The eye color follows a polygenic inheritance pattern. In humans, 9 eye colors are recognized. Phenotypic expression of eye color is controlled by two major genes and 14 additional genes, which are linked to X chromosomes. Different combinations of these alleles result in a variety of eye colors. The eye color is due to the presence of melanin in the front portion of the iris.

Black and brown eye color has a high amount of melanin in comparison to the hazel or green eye color while the complete absence of the melanin results in blue eye color. Dominant allele BBGG contributes to the melanin synthesis in the iris that results in black eye color while the combination of all recessive alleles bbgg results in blue eye color. The rest of all the eye colors are the combination of these dominant and recessive alleles.

See below:. 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 disease in question, there are a few ways in which they can be inherited from our parents:. Regardless of how the disease was inherited, monogenic diseases are easier to test for than polygenic diseases, because we simply need to look for the presence or absence of a faulty gene.

The vast majority of diseases we are familiar with are actually polygenic diseases. These diseases are influenced by genetic variations in many genes. They are also often influenced by many environmental factors, like nutrition, exercise, and environmental exposures.

Polygenic diseases typically affect millions of people in the population, and are usually diagnosed during your adult years. An additional 88 million Americans over the age of 18 years are considered prediabetic, meaning they have a high risk of developing Type 2 diabetes. Perhaps you would alter their lifestyle to include more exercise and sports. The reason polygenic diseases affect so many people is because they all involve so many different genes - often in different combinations - that interact with different environmental factors to cause the disease.

See why they are so complex? For single-gene, monogenic diseases, couples can undergo carrier screening prior to conception. The results of these tests tell you whether you are likely to be a carrier of genetic disorder or not.

Predicting genetic risk for polygenic diseases is far more complex than carrier screening. With advances in genomics and massive DNA databases, scientists can determine which variations increase or decrease risk of a particular disease. Many couples now opt for genetic screening before or during pregnancy. The question then becomes: what can we do with this information? We believe that knowledge is power at Orchid. Couples can use our reports to make informed choices about family planning, embryo screening, and lifestyle modifications to maximize their chances of bringing and raising a healthy child in this world.

In summary, it is of great importance to understand these inheritance patterns in order to understand the manner in which different traits are expressed in organisms. The two main forms monogenic inheritance and polygenic inheritance represents the traditional Mendelian inheritance pattern and the later discovered Non — Mendelian inheritance patterns, respectively.

In these two patterns, the inheritance is governed by the number of genes involved in determining the particular trait or phenotype or character of an organism. Thus, monogenic, as the name suggests, uses one gene to determine a character; in contrast, polygenic patterns involve more than one gene to give rise to a single character. This is the difference between monogenic and polygenic inheritance.

The study of the genes involved in these inheritance patterns is important as it helps to study mutations of genes which give rise to genetic disorders and to build up genetic relationships among organisms for a common character and thereby evaluate evolutionary traits.

You can download PDF version of this article and use it for offline purposes as per citation notes. Available here. Samanthi Udayangani holds a B. Degree in Plant Science, M. Your email address will not be published. Leave a Reply Cancel reply Your email address will not be published. Monogenic vs Polygenic Inheritance.

Monogenic inheritance is an inheritance pattern which determines a particular trait by one set of alleles or a specific gene. Polygenic inheritance is an inheritance pattern which determines a particular trait by more than one set of alleles or more than one gene. Number of Genes Involved.

Only one gene is involved in determining the character in monogenic inheritance. Two or more genes are involved in determining a single character in polygenic inheritance.