Homologous Structures

(a) What are homologous structures? Give an example. (b) "The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it." Justify this statement with the help of a flow chart showing sex-determination in human beings.

(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 ?

Example of homologous structure is // are :

Clitoris of female and Glans of penis of male are homologous/analogous structures.

Which of the following statement/s is/are wrong? I. Homology is based on divergent evolution whereas analogy refers to a situation exactly opposite. II. The thorn and tendrills of Bougainvillea and Cucurbita represent homology III. Analogous structures are a result of divergent evolution. IV. Darwin's finches represent one of the best examples of adaptive radiation.

Homologous Series

Which of the following structure is homologous to penis ?

Which of the following structures is homologous to the wing of the birds ?