CBSE Class 10 Science 2019 · Paper 31/1/1/C · Question 19

(a) (i) Mendel crossed pure tall pea plants ($\text{TT}$) with pure short plants ($\text{tt}$). All the ${\text{F}}_1$ plants were tall; none was short or of medium height. When the ${\text{F}}_1$ plants were self-pollinated, the ${\text{F}}_2$ had tall and short plants in the ratio $3:1$. The short trait hidden in the ${\text{F}}_1$ reappeared, so the ${\text{F}}_1$ plants carried it without showing it: the trait that is expressed (tallness) is dominant and the one that is hidden (shortness) is recessive. (ii) Mendel crossed pure plants having round, yellow seeds ($\text{RRYY}$) with pure plants having wrinkled, green seeds ($\text{rryy}$). All the ${\text{F}}_1$ plants had round, yellow seeds. On self-pollination of the ${\text{F}}_1$, the ${\text{F}}_2$ had round yellow, round green, wrinkled yellow and wrinkled green seeds in the ratio $9:3:3:1$. New combinations (round green and wrinkled yellow) not present in either parent appeared, so seed shape and seed colour are inherited independently of each other. (b) The statement is not correct. The wings of birds and bats are analogous organs: they have the same use, flying, but a different design, since a bat's wing is a fold of skin stretched between elongated fingers while a bird's wing is a feathery covering all along the arm. A common use does not show close relationship. Bats share far more basic features with squirrels (both are mammals with hair that give birth to young ones and feed them milk), and birds with lizards (both lay eggs with shells, and birds evolved from reptiles). So bats are more closely related to squirrels, and birds to lizards.