Sexual Reproduction in Living Organisms!
Sexual reproduction involves the two sexes, namely, male and female. The male sexual unit is known as male gamete, while the female sexual unit is known as female gamete.
The formation of gametes and their fusion constitute sexual reproduction. The male gamete is smaller and more active than the female gamete.
The female gamete is larger, filled with reserve food and remains passive.
The cell formed after the fusion of the male and female gametes is called zygote. The zygote divides repeatedly to form a new individual. Although sexual reproduction also occurs in unicellular organisms like algae and Paramecium, it is most common in multicellular organisms.
Genetic basis and advantage of variations:
You know that variations help in the survival of a species over time. During asexual reproduction cells divide and DNA replication takes place. At the time of replication, some variation may occur but this variation does not usually cause any drastic change.
So, in asexual reproduction offspring are more or less similar to the parent and variation is slow. During sexual reproduction two types of gametes (male and female) are formed. During the fusion of gametes there is recombination of genetic material from two parents. This leads to greater variation in the offspring. As the offspring gets more variations, it is more likely to adjust better to environmental fluctuations.
Gametes contain half the usual number of chromosomes:
During sexual reproduction, the combination of DNA from two parents would result in the offspring having twice the amount of DNA. To solve this problem, sexually reproducing individuals have special germ cells (gametes) with only half the normal number of chromosomes and, therefore, half the amount of DNA compared to the other cells of the body. When such germ cells from two individuals unite during sexual reproduction, the normal chromosome number and DNA content are restored.
Significance of sexual reproduction:
Sexual reproduction results in new combinations of genes that are brought together during gamete formation. This reshuffling of genes in the gametes increases the chances of variation in the offspring. Moreover, the combination of two sets of chromosomes, one set from each parent, during zygote formation, leads to variation within a species.