a) No two individuals are absolutely alike in a population. Why? 3 b) How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations? 3 c) What happens when: (i) Accidentally, Planaria gets cut into many pieces? (ii) Vas deferens of a male gets blocked ?
Answers
Answer:
(a)No two individuals in the population are exactly alike.
The reason behind this is the variations occurred during the process of DNA copying. These variations are generated due to two main reasons.
They are; crossing over of DNA and recombination of DNA during DNA copying process. This makes every individual different from the others.
(b)In both sexual and asexual reproduction, there is great importance of maintaining a constant number of chromosomes. But the process mechanism is dissimilar in both the type of reproductions.
(1) In case of asexual reproduction, the entire set of chromosomes is replicated and transferred to the next generation. DNA copying is accompanied by the creation of an additional cellular material, after which the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells. Thus, chromosome number remains unchanged. For example: Replica of Amoeba by binary fission.
(2) In case of sexual reproduction, the chromosome number is halved to form gametes. Then these gametes combine to restore the original chromosome number. For example: In the case of human beings they have 46 chromosomes present in a cell, during reproduction gametes are generated which include half the number i.e. 23. Now, when female gamete containing 23 chromosomes is combined with male gamete with 23 chromosomes, the number is restored to original 46 (23+23)
(c)(i)When planaria is cut into many pieces it undergoes regeneration and each piece forms a new individual.
(ii)When the male vasa deferentia are blocked, it prevents the sperm from entering into the seminal glands or the ejaculate (semen). No sperms in the semen means no fertilization with the egg.