CBSE Class 10 Science 2020 · Paper 31/5/1 · Question 20

(a) Tallness is the dominant trait. Every F1 plant receives a factor for tallness (T) from the tall parent and a factor for shortness (t) from the short parent; being Tt, it shows only the dominant trait, so all F1 plants are tall. (b) The F1 plants are all tall, but the F2 contains both tall and short plants, in the ratio $3:1$. The reason: the recessive character, shortness, is expressed in the F2 generation when two copies of the recessive factor come together in a plant (tt). (c) Conclusion: in the F2 progeny the dominant character is expressed along with the recessive character in the ratio $3:1$; the recessive trait was not lost in the F1 but only hidden, because each trait is controlled by a pair of factors, one inherited from each parent.