How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations? Explain with the help of suitable example.
During asexual reproduction, organisms undergo only mitotic cell divisions . The DNA of the cells involved are replicated and then divided evenly among the two daughter cells formed. Thus, the chromosome number remains unchanged.
During sexual reproduction, organisms undergo meiosis ie., the chromosome number is halved to form gametes. Two gametes fuse together to form the zygote and thus the chromosome number is restored.
Example: In humans, each parent has 23 pairs of chromosomes. In the gametes, the sperms have half the number of chromosomes , i.e. 23 and the egg also has 23 chromosomes . When the sperm and the egg fuse , the zygote is formed having 23 pairs or 46 chromosomes. Thus, the chromosome number remains constant.