"An individual cannot pass on to its progeny the experiences of its life-time." Justify the statement with the help of an example and also give reason for the same.
"An individual cannot pass on to its progeny the experiences of its life-time." Justify the statement with the help of an example and also give reason for the same.
Only those traits that are controlled by genes (DNA of germ cells/reproductive cells) can be passed from parents to offspring. Experiences acquired during an individual's lifetime usually bring about changes in the somatic (body) cells only and not in the germ cells, so they cannot be transmitted to the next generation.
Example: If a mouse's tail is cut off, the mouse will live its whole life without a tail, but its babies (progeny) will still be born with a tail. This is because the change occurred in the body cells of the mouse, not in the reproductive cells (gametes). Similarly, a wrestler develops strong muscles through exercise, but his children are not necessarily born with stronger muscles; they must exercise to build them.
Reason: Inherited information is carried by the genes present in the DNA of the gametes (sperm and egg). Changes that happen in the non-reproductive body cells during life are called acquired traits and these are not written into the DNA of the germ cells, hence they are not inherited.
Marking Scheme
- 11 mark: Definition/idea that only germ-cell DNA is passed to progeny.
- 21 mark: Correct example (e.g., cut tail of mouse / wrestler building muscles).
- 31 mark: Proper reason — changes are in somatic cells, not in gametes, hence not inherited.
Hint
Think about which type of cell passes genetic material to the next generation — body cells or germ cells? Use the textbook example of a tailless mouse.
Quick Oral Answer
Because changes that occur in the non-reproductive (somatic) cells of the body during an organism's lifetime are not carried by the DNA of the gametes; hence the progeny receives unchanged genetic information.
Analysis & Explanation
The question tests the concept that heredity operates through genes (DNA) carried in the gametes. NCERT emphasises that inherited traits are due to gene differences, while modifications brought about during life (acquired traits) are generally not inherited. The given NCERT example of cutting a mouse's tail, and the general concept that only germ-cell DNA passes to the next generation, justify the statement.
Common Mistakes
- 1Writing only the example without the underlying reason (loss of 1 mark).
- 2Confusing 'acquired traits' with 'inherited traits'.
- 3Saying experiences can change germ-cell DNA — incorrect.
Interesting Facts
Even Charles Darwin's 'pangenesis' (now disproved) once tried to explain how body changes could reach the gametes — Weismann's experiment on mice finally disproved this.
Lamarck's theory of inheritance of acquired characters was disproved by August Weismann by cutting off mouse tails for 22 successive generations.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2012?
This question carries 3 marks in the CBSE Class 10 Science 2012 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Heredity" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Acquired traits and inheritance" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2012 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.