CBSE Class 10 Science 2019 · Paper 31/2/2 · Question 16

(a) Dominant trait: of a pair of contrasting traits, the one that is expressed in the ${\text{F}}_1$ (first) generation after a cross; it shows even when only one factor for it is present. Recessive trait: the contrasting trait that is not expressed in the ${\text{F}}_1$ generation although it is inherited; it shows only when both factors for it are recessive. (b) Yes. Example: Mendel crossed pure tall pea plants ($\text{TT}$) with pure short ones ($\text{tt}$). All the ${\text{F}}_1$ plants were tall ($\text{Tt}$): each had inherited the factor for shortness ($\text{t}$) from its short parent, but it was not expressed because tallness is dominant. When the ${\text{F}}_1$ plants were self-pollinated, the ${\text{F}}_2$ generation had tall and short plants in the ratio $3:1$ ($\text{TT}$, $\text{Tt}$, $\text{Tt}$ : $\text{tt}$). The short trait reappeared, showing that it had been inherited by the ${\text{F}}_1$ plants without being expressed in them.