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SAI International School
Subject-Biology, Class- X
Chapter- How do Organisms Reproduce?
Subtopic- DNA Copying, Variation,
Asexual Reproduction- Fission, Fragmentation
Module-18
Lesson Notes

1. Do organisms create Exact copies of themselves?

 Asexually reproducing organisms can create exact copies of themselves. But it is
impossible that all organisms produce similar organisms. In sexually reproducing
organisms, there is variation due to combination of genes. The variation may be
in their structural and physical appearance.

 A basic event in reproduction is the creation of a DNA copy. Cells generate
copies of DNA during reproduction by involving several chemical processes.
Thus, the copies of DNA generated will be similar as the process is same but
may not always be identical due to variations.

 DNA copying is an important phenomenon of reproduction through which the
organisms pass on their characteristics to their offspring. It maintains the
characteristics in different generations of the species. It also produces variations
which are useful for the survival of species for a long time.

2. The importance of variation

Variations are differences found in morphological, physiological and other traits of
individuals belonging to the same organism, race or family.

 Genetic variation can be caused by -
(i) Faulty DNA replication
(ii) mutation (which can create entirely new alleles in a population)
(iii) random mating between organisms
(iv) random fertilization
(v) crossing over or recombination

 Variation helps in survival of the organism in different ways -
(i) It helps a species to survive.
(ii) It also helps organisms to adapt to their environment as well as to changes
which occur in the environment.
(iii) It also helps a species to emerge strong if favoured by natural selection.

 Useful variations give advantage to Individuals in obtaining more food,
reproduction, adaptation to environmental changes and higher success in the

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