Heredity and Evolution / Mapping our Genes – Variation
“The act or process of changing (in genetics) in the characters or traits in an individual from the group to which it belongs or deviation in characters of the offspring from those of its parents is called variation.”
During reproduction, the organism uses its own body material. A simple cell duplicates its genetic material (DNA copying) and passes it on from generation to generation. In the process of DNA copying, some variations take place
every time. Thus, DNA copies (next generation) are similar but not identical (subtly different) to the original. This tendency of variation during reproduction leads to evolution.
The changes are produced at the genetic level as organisms’ genes mutate and/or recombine in different ways during reproduction and are passed on to future generations. Non-genetic changes that occur during an organism’s life span, such as increases in muscle mass due to exercise and diet, cannot be passed on to the next generation and are not examples of evolution.
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The importance of Variations
(a) They play an important role in survival and adaptability of a species. Drastic alteration in ecological system due to uncontrolled conditions such as variation in earth temperature, water levels, meteorite hit etc. can extinct a species. However, if some variations were to be present in a few individuals in the population which are suitable for new environment, there would be some chance of survival of that species.
Thus, variation is useful for the survival of species over time.
(b) They are responsible for evolution and for the development of new species.
I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.
– Charles Darwin, The Origin of Species
Accumulation of Variation during Reproduction –
- Asexual reproduction is the process by which an organism creates a genetically similar or identical copy of itself without a contribution of genetic material from another individual.
- The offsprings have very minor differences because of small inaccuracies involved in DNA copying.
- Sexual reproduction is a biological process by which organisms create descendants that have a
combination of genetic material contributed from two different members (male and female) of the species. Each of two parent organisms contributes half of the offspring’s genetic makeup by creating gametes.
- The offsprings show greater diversity / variations from their parents due to crossing over and exchange of gene segments.