Gene interaction for a single phenotype

            We are all very familiar with the Mendelian studies, which show the independent gene assortment for each trait analysed in the peas. However, genes frequently do not act independently in their phenotypic expression. Gene interaction is the term used to call the interaction between expressions of genes at different loci. The effects of genes at one locus depend on the expression of genes at other loci (Pierce, 2008). Thus, the phenotype is not predictable from the perspective of a single locus effects alone, as the products of genes at different loci blend to produce the phenotype.

Figure 1: Gene interaction in fruit colour of Capsicum annum (Pierce, 2008) 

                The fruit colour in the pepper Capsicum annuum is a simple example of gene interaction between two loci producing a single trait. The Y locus and the C locus interact to form the colours. When two heterozygous cross with each other (YyCc x YyCc) the four possible colours of pepper fruit are present in the offspring in a proportion of 9:3:3:1, which are red, peach, orange and cream (Pierce, 2008). You can see on the picture the genotype for each colour.

                

Figure 2: Some coat colours in mice
 (Griffiths, 2000)

         
More complex gene interaction is observed in the genetics of coat colour of mammals. In dogs, many genes participate, and several loci interact with each other. The expression of a particular gene is modified by the effects of other genes. There are four most recognized loci producing many of the noticeable differences in colour and pattern among breed of dogs. However, other poorly known loci may modify the effects of these loci (Pierce, 2008).  In mice, five main genes interact to determine the coat colours (Griffiths et. al. 2000).

                In humans a set of genes are involved in the production of melanin, which provides colour for skin, hair and eyes. Mutations in any of these genes disturb the production of melanin, which reduces pigmentation in the skin, hair, and eyes and causes albinism. Mutations in six genes have been related to be responsible for different types of albinism (Oetting & Kin, 1999).

Figure 3: Albinism in humans

REFERENCE LIST

Griffiths AJF, Miller JH, Suzuki DT, Lewontin RC, Gelbart WM (2000). Gene interaction in coat color of mammals. In An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman.

Oetting, WS and King, RA (1999), Molecular basis of albinism: Mutations and polymorphisms of pigmentation genes associated with albinism. Hum. Mutat., 13: 99–115

Pierce BA (2008). Genetic Maternal Effect. In: Genetics: A Conceptual Approach. (third edition) W. H. Freeman and Company, New York. pp 105-114

Figure 3: http://foter.com/search/instant/?q=albinism