(a) If we cross pure - bred tall (dominant ) pea plants with pure - bred dwarf ( recessive ) pea plant we get pea plants of ` F_ 1 ` generation. If we now self- cross the pea plants of ` F_1 ` generation, then we obtain pea plants of ` F_ 2 ` generation.
(i) What do the plants of `F_1 ` generation look like ?
(ii) What is the ratio of tall plants dwarf plants in ` F_2 ` generation ?
(iii) State the type of plants not found in ` F_1 ` generation but appeared in ` F_2 ` generation, mentioning the reason for the same.
(b) What are homologous structures ? Give an example. Is it necessary that homologous structures always have common ancestors ?

Explanation

(a) (i) All the plants in ` F_1 ` generation plants appear tall.
(ii) The ratio of the tall plants to dwarf plants in ` F_ 2 ` generation is 3 (tall) : 1 (dwarf).
(iii) Dwarf plants do not appear in ` F_ 1 ` generation as dwarfness is the recessive trait. According to Mendel's Law of Dominance, the trait which expresses itself in the hybrid is called dominant and the other which is unable to express itself is the recessive trait.
(b) The structures which have same basic structures but different functions in different species are homologous organs.
For Example, Wings of birds and arms of man.
Yes, it is necessary that homologous structures always have a common ancestor in order to carry out the different activities. Otherwise there cannot be any similarly in basic pain, internal structure development or origin.