Final answer:
In Mendelian genetics, homozygous recessive plants are not seen in the F1 generation, which consists entirely of heterozygous offspring, due to the Law of Dominance. The homozygous recessive phenotype reappears in the F2 generation upon cross-pollination of two F1 heterozygous plants, producing all possible genetic combinations of the alleles.
Step-by-step explanation:
In Mendelian genetics, the type of plants not obtained in the F1 generation were homozygous recessive. The F1 generation comprised entirely of heterozygous individuals due to the cross of two homozygous parents with contrasting traits. The reason for the absence of homozygous recessive plants in the F1 generation is the Law of Dominance, which states that the dominant allele masks the expression of the recessive allele in a heterozygous organism. Consequently, the homozygous recessive phenotype does not appear in the F1 generation.
In the subsequent F2 generation, however, the recessive traits reappeared. This occurs when two F1 plants carrying the recessive allele (heterozygous) are cross-pollinated. The offspring have a chance of being homozygous recessive since the F2 progeny can inherit a recessive allele from each parent. Thus, the F2 generation displays all possible genetic combinations of the alleles, including homozygous dominant, heterozygous, and homozygous recessive in a typical 1:2:1 genotypic ratio, with the recessive phenotype manifesting in one-quarter of the offspring, assuming a single gene with two alleles and complete dominance.