NCERT Solution for Class 10 Science Chapter 9
Heredity and Evolution
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-159
Questions No-10
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
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Variations arise either because of errors in DNA copying, during asexual reproduction, which will be fewer; or because of fusion of gametes from two individuals in sexual reproduction. Since, in sexual reproduction, gametes from two different individuals with different genetic make up, are involved so variations are much higher.
During sexual reproduction, genotype of the progeny is contributed by two different individuals. This opens up scope for various permutations and combinations. Moreover, the crossing over during meiosis is another means for producing variations. Hence, there are more chances of variations during sexual reproduction than during asexual reproduction.
Sexual reproduction causes more viable variations due to the following reasons:
1. Error in copying of DNA, which are not highly significant.
2. Random seggregation of paternal and maternal chromosome at the time of gamete formation.
3. Exchange of genetic material between homologous chromosomes during formation of gametes.
4. Accumulation of variations occured due to sexual reproduction over generation after generation and selection by nature created wide diversity.
In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.
In sexual reproduction, two individuals having different variations combine their DNA to
give rise to a new individual. Therefore, sexual reproduction allows more variations,
whereas in asexual reproduction, chance variations can only occur when the copying of
DNA is not accurate.
Additionally, asexual reproduction allows very less variations because if there are more
variations, then the resultant DNA will not be able to survive inside the inherited cellular
apparatus.
However, in sexual reproduction, more variations are allowed and the resultant DNA is
also able to survive, thus making the variations viable.
Variation and Evolution: Variants help the species to survive in all the conditions.
Environmental conditions such as heat, light, pests, and food availability can change
suddenly at only one place. At that time, only those variants resistant to these conditions
would be able to survive. This will slowly lead to the evolution of a better adapted species.
Thus, variation helps in the evolution of sexually reproducing organisms.
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