Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance. (i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce $\mathrm{F}_1$ progeny, which two observations were made by him in $\mathrm{F}_1$ plants? (ii) Write one difference between dominant and recessive trait. (iii) (A) In a cross with two pairs of contrasting characters RRYY $\times$ rryy (Round Yellow) (Wrinkled Green) Mendel observed 4 types of combinations in $\mathrm{F}_2$ generation. By which method did he obtain $\mathrm{F}_2$ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment. OR (iii) (B) Justify the statement: 'It is possible that a trait is inherited but may not be expressed.'

(i) Mendel observed that in the $F_1$ progeny: (a) All plants were tall, meaning only one of the parental traits was expressed. (b) There were no 'medium-height' plants, indicating no blending of traits.

(ii) A dominant trait (e.g., Tallness '$T$') is expressed in the phenotype even if only one copy of the allele is present (heterozygous condition, $Tt$). A recessive trait (e.g., Shortness '$t$') is expressed only when two copies of the allele are present (homozygous condition, $tt$).

(iii) (A) Mendel obtained the $F_2$ generation by self-pollination (selfing) of the $F_1$ plants. The ratio of parental combinations (Round Yellow and Wrinkled Green) in $F_2$ is $9:1$ (out of the $9:3:3:1$ phenotypic ratio). Conclusion: Traits are inherited independently of each other (Law of Independent Assortment).

OR

(iii) (B) In Mendel's monohybrid cross, when pure tall ($TT$) and pure short ($tt$) plants were crossed, the $F_1$ progeny were all tall ($Tt$). The 'short' trait was inherited from the parent but was not expressed because the 'tall' allele was dominant. However, this trait reappeared in the $F_2$ generation ($tt$), proving it was present but hidden in $F_1$.