The phenotypic and genotypic ratios obtained from monohybrid cross done by Mendel respectively are2 : 3 and 1 : 2 : 21 : 1 and 1 : 2 : 13 : 1 and 1 : 2 : 19 : 3 and 3 : 1

The phenotypic and genotypic ratios obtained from a monohybrid cross done by Mendel are respectively 3:1 and 1:2:1.

Here's the step by step explanation:

1. A monohybrid cross is a breeding experiment between P generation (parental generation) organisms that differ in a single given trait. In Mendel's experiments, he used pea plants, and for a monohybrid cross, he would control the pollination process to ensure that one plant had two copies of one allele, and the other plant had two copies of the other allele for a particular trait.

2. The F1 generation (first filial generation) would all express the dominant trait, but they would be heterozygous, having one copy of the dominant allele and one copy of the recessive allele.

3. When Mendel allowed the F1 generation to self-pollinate, the F2 generation (second filial generation) showed a phenotypic ratio of 3:1. This means that three out of four plants had the dominant trait, and one out of four plants had the recessive trait.

4. However, the genotypic ratio was 1:2:1. This means that one out of four plants was homozygous dominant (having two copies of the dominant allele), two out of four plants were heterozygous (having one copy of each allele), and one out of four plants was homozygous recessive (having two copies of the recessive allele).