Experimental support for Mendel's law of segregation comes from the results of self-fertilizing F2 plants that display the dominant phenotype. Based on the law of segregation, what proportion of the dominant F2 plants would be expected to produce F3 progeny phenotypes in a ratio of 3 dominant : 1 recessive?

2/3

Explanation:

When two heterozygous plants (let's suppose Tt and Tt) are crossed, the progeny exhibits dominant and recessive phenotype in a 3 : 1 ratio respectively. This occurs since T and t alleles present together in the heterozygous parent plant segregate from each other and are distributed to the different gametes.  

Cross Tt x Tt= 1/4 TT: 1/2 Tt: 1/4 tt

Considering the genotype of the F2 progeny, there is 2/3 heterozygous dominant progeny (Tt) out of a total of 3/4 dominant progeny. This heterozygous dominant progeny would give a 3:1 ratio of dominant and recessive progeny upon self-fertilization.

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