Linkage in Maize

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                                                              Linkage in Maize

 

Hutchison experimentally proved the existence of linkage in maize (Zea mays). In maize, coloured seed (CC) is dominant and colourless seed is recessive (cc). Full seed (endosperm) is dominant (FF) and shrunken seed is recessive (ff).

A cross was made between coloured full seeded plant with colourless shrunken seeded plant. The genes for seed colour a shape are linked. i.e. C and F are linked; c and f are linked. T linked genotypes of the parents are written as follows. Colourless shrunken seeded plant cf/cf , Coloured full seeded plant CF/CF

All the F1 plants are coloured and full and the genotype written as CF/cf A test cross is made by crossing the F1 plant (CF/cf) with double recessive plant (cf/cf). In the F2 generation, plants were obtained in the ratio of 48.2: 1.8: 1.8:48.2.

Coloured full CF/cf - 48.2%

Coloured shrunken Cf/cf - 1.8%

Colourless full cF/cf - - 1.8%

Colourless shrunken cf/cf - 48.2%

If Mendelian independent assortment occurred in this experiment, the F2 ratio should be 1:1:1:1.

Here, the parental combinations are in large numbers and new combinations are very less. 96.4% of the plants are in parental combinations and only 3.6% of the plants are in new combinations. This shows clearly genes C and F have not assorted independently; so also c and f. That means 96.4% is due to linkages and 3.6% is due to break of linkage; that is crossing over.


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