Non-Mendelian In Heritance
According to Mendel's law, phenotypic ratio of F2 generations in dihybrid cross is 9 : 3 : 3 : 1. However, in several cases the phenotypic ratio of F2 generation does not match Mendel's law. Nevertheless, the ratio that appears still ranges in 9 : 3 : 3 : 1. For example, 15 : 1 or (9 + 3) : I and 12 : 3: 1 or (9 + 3) : 3 : 1. This condition is called non-Mendelian inheritance. Several cases of non-Mendelian inheritance axe gene interaction between Loci, epistasis-hypostasis, polygenic, and cryptomeri.
Epistasis and Hypostasis
During epistasis and hypostasis there occurs interaction between dominant genes located in different locus (non- Homologous dominant gene). The two dominant genes influence each other and some of the dominant genes cover up other dominant genes.
Epistasis-hypostatis occurs due to the interaction between dominant genes located in different locus
Dominant gene that covers up other dominant genes Is called epistasis gene, while dominant gene that is suppressed is called hypostasis’ gene. Epistasis-hypostasis case can be found in color formation of wheat husk. There are three colors of wheat husk which are black, yellow, and white. The dominant allele H determines the color of black wheat husk and is Dominant to h. Dominant allele K determines the color of Yellow husk and dominant to k. AIIeIe H is epistasis to allele K, or allele is hypostasis to allele H It means, when allele H appears at the same time with allele K, the color of husk Is black. The yellow husk is formed if the appearance of allele K is not at the same time with allele H, while white husk is formed if the alleles that appeir are all recessive. Therafore, the genotype probabilities for black husk are HHKK, HHKk, HhKK, HhKk, HhKk, Hhkk; the yellow husk are hhKK and,hhKk; and the white husk is hhkk.
Polygenic is a heredity pattern signed by the determination of one trait by many alleles. The example of polygenic in human is the trait formation of height, weight, Skin color, eye color, intelligence, and body shape.
One example of cross in polygenic case
In the formation of human skin color, the determiner allele are A –a and, B-b. Human skin colors, generally, are only blank and white. But there are variations in black skin color
Starting from black, dark brown, mulatto, and light Brown. The variation is determined by the number Of dominant gene in a person's genotype.
The Number Of Dominant Gene In a Person's Genotype
Cryptomere are the non-allele dominant genes that seem hidden when They stand alone and the influence will appear after dominant genes appear At the same time. Cyptomere can be found in the formation of linaria flower (Linaria maroccana).
In Cryptomery, the influence of dominant genes will appear when they appear at the same time
The crossing between red linaria and white linaria produces purple linaria as the F1. If the offsprings are crossed each other, the phenotypic ratio of F2 generation produced is 9 purple : 3 red :4 white. The ratio can be declined into 9 : 3 : (3+1).
In advanced experiment it was found two Determiner factors of the color formation in linaria flower, which are the presence or absence of antocyanin pigment and pH condition in cell plasma The gene forming antocyanin is dominant, while the one that acts as acid environmental determiner is recessive.
Based on picture In Cryptomery, the influence of dominant genes will appear when they appear at the same time ,It is known that purple color is the hidden color. The color will appear if two dominant genes appear at the same time. The genotype possibilities for red flower are Aabb and. Aabb; those for purple flower are AABB, AABb, AaBB, and, AaBb; and those for white flower are aaBb. aaBb, and, aabb.
Source: Essential Biology, 2006.