How to find a number of genes controling the trait

Polygenic inheritance refers to the kind of inheritance in which the trait is produced from the cumulative effects of many genes in contrast to monogenic inheritance in which the trait results from the expression of one gene (or one gene pair). In monogenic inheritance, the expression may be predicted according to a phenotypic ratio that follows Mendelian inheritance. Polygenic inheritance is a non-Mendelian form since it is controlled by multiple genes at different loci on different chromosomes expressed together in the same trait. For example, if one pair of genes controls color, and red is dominant to white, then when you cross two heterozygotes (Aa), red and white progeny will appear in the ratio of 3:1. However, if two pairs of genes control color and the dominant allele at both loci must be expressed to get red flowers, then crossing two heterozygotes (Aa Bb) will give you red and white flowers in a ratio of 9:7. This is a modification of the typical dihybrid Mendelian ratio of 9:3:3:1, in which three of the progeny groups all have the same phenotype. Polygenic Inheritance Definition What is polygenic inheritance? Polygenic inheritance, in simple terms, implies a character or phenotypic trait, which is regulated by more than one gene. In biology, it refers to the quantitative inheritance wherein two or more independent genes additively affect a single phenotypic trait. In a way, polygenic inheritance is a multiple factor inheritance or multiple gene inheritance, or multifactorial inheritance. Thus, polygenic inheritance is the phenotypic trait that is not a single gene trait but a cumulative expression of multiple genes. It is important to note that polygenic inheritance is different from Mendelian Inheritance in terms of pattern and expression. In Mendelian Inheritance, each phenotypic trait is monogenic, meaning the expression of this trait is either expressed or masked based on it being ‘a dominant’ or ‘a recessive’ gene. In polygenic inheritance, the expression of the phenotypic trait does not display complete dominance wherein the phenotypic expression of a trait in an offspring is a mixture or additive of traits displayed in parents. In polygenic inheritance, there is an additive of the traits present in the parents. This type of inheritance pattern is known as the polygenic inheritance pattern. 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.e. polygenes). Etymology: “poly”, meaning “many”. Compare: monogenic inheritance. Related term: polygene. What are polygenic inheritance examples? 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. Accordingly, traits, such as height or skin color, cannot be categorized as ‘tall’ or ‘short’ / ‘light’ or ‘dark’. These traits exhibit multiple and continuous variations of the phenotype. Polygenic inheritance is controlled by two types of alleles or genes, namely: Contributing alleles: Alleles that contribute to continuous variation are referred to as contributing alleles Non-contributing alleles: Alleles that do not contribute to continuous variation are referred to as non-contributing alleles. These alleles are sometimes referred to as effective and non-effective alleles, respectively. Characteristics of Polygenic Inheritance A gene that employs a minor effect on a phenotype along with other genes is referred to as polygenes. The effect of an individual gene is too minor and often remains undetected Numerous genes exert an equal effect. Individually, each allele contributes to the result in a cumulative or additive manner The expression of one gene is not masked by the presence of the other genes, i.e., epistasis is not involved. The gene involved in polygenic inheritance is either contributing (active allele) or non-contributing (null allele); there are no genes as dominant or masked genes. There is a continuous variation of the phenotype of a trait in a polygenic inheritance The polygenic inheritance pattern is difficult to predict and it is highly complex. The statistical analysis of polygenic inheritance patterns can help to provide an estimate of population parameters. Most of the polygenic inheritance follow the normal distribution curve, wherein the majority of the people fall in the middle range of the curve. Polygenic inheritance is different from multiple alleles. In multiple alleles, on the same locus, three or more alleles are present an organism, e.g. human blood group system, i.e., the ABO system, is controlled by three alleles. #QuantitativeTraitLocus #NikolaysGeneticsLessons #PolygenicInheritance #polygenicInheritanceExample #whatIsPolygenicInheritance #normalDistributionCurve #incompletelyDominantTraits #additiveEffect #genetics #exampleOfPolygenicInheritance #skinColorTrait #skinColorTr