FORKED-LINE METHOD

FORKED-LINE METHOD

4.   FORKED-LINE METHOD

For three or more unlinked events, Punnett square method is quite difficult. With three unlinked genes, each parent can produce 8 different types of gametes, which generates 64 possible genotypic combinations in the Punnett Square. 
For four unlinked genes, there are 16 possible gametes from each parent and 256 cells in the complete it is, therefore, more effective to use the forked-line method when working with 3 or more traits.  The forked-line method is based on possible alternatives using fractions, rather than all possible fertilization events. The forked-line can be used to figure out phenotypic probability, and to figure out genotypic probability. 
Each branch point represents the expected distribution of phenotypes or genotypes for a particular trait based on parental genotypes. Multiplying the expected fractions at each of the branches across the diagram provides an easy calculation of the expected frequency of any particular phenotypic or genotypic combination. 


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