Interaction of genes
About Interaction of genes
Genes interaction is the influence of alleles and non-alleles on the normal phenotypic exprssion of genes. It is of two types.
Types of Interaction of genes
(1) Inter–allelic or intra–genic gene interaction : In this case two alleles (located on the same gene locus on two homologous chromosomes) of gene interact in such a fashion to produces phenotypic expression e.q. co-dominance, multiple alleles.
(i) Incomplete dominance (1:2:1 ratio) : After Mendel, several cases were recorded where F1 hybrids were not related to either of the parents but exhibited a blending of characters of two parents. This is called incomplete dominance or blending inheritance.
Example : In 4-O’clock plant, (Mirabilis jalapa), when plants with red flowers (RR) are crossed with plants having white flowers (rr) the hybrid F1 plants (Rr) bear pink flowers. When these F1 plants with pink flowers are self pollinated they develop red (RR), pink (Rr) and white (rr) flowered plants in the ratio of 1:2:1 (F2 generation).
Example : In Snapdragon or dog flower (Antirrhinum majus) the dominant character of leaf (Broadness) and flower (Red) shows incomplete dominance over recessive characters (Narrowness and white) in dihybrid cross.
(ii) Codominance (1:2:1 ratio) : In codominance, both the genes of an allelomorphic pair express themselves equally in F1 hybrids. 1:2:1 ratio both genotypically as well as phenotypically in F2 generation.
Example : Codominance of coat colour in cattle.
In cattle gene R stands for red coat colour and gene r stands for white coat colour. When red cattle (RR) are crossed with white cattle (rr), the F1 hybrids have roan coloured skin (not the intermediate pink). The roan colour is actually expressed by a mixture of red and white hairs, which develop side by side in the heterozygous F1 hybrid. In F2 generation red, roan and white appear in the ratio of 1 : 2 : 1. The phenotypic ratio equal to genotypic ratio RR, Rr, rr (1 : 2 : 1).
Example : Codominance in andalusian fowl
In andalusian fowl a cross between pure black and pure white varieties results in blue hybrids.
Example : Codominance of blood alleles in man
(a) MN blood type in man is an example of codominance. The persons with MN genotype produce both antigen M and N and not some intermediate product indicating that both the genes are functional at the same time.
(b) In ABO blood group system gene A and B responsible for blood group A and B are codominant. The hybrid has AB blood group.To excel in your Biology exam must refer NCERT text book and solve the questions given in exercise of NCERT for reference you can use Physics Wallah NCERT solutions for class 12 biology . Prepared by Physics Wallah experts
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