(a) What is variation ? List two main reasons that may lead to variation in a population. OR (b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the progeny. (ii) If the plants of progeny are self-pollinated, then what would be observed in the plants of progeny ? (iii) If 100 plants are produced in progeny, then how many plants will show the recessive trait ?
(a) What is variation ? List two main reasons that may lead to variation in a population. OR (b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the progeny. (ii) If the plants of progeny are self-pollinated, then what would be observed in the plants of progeny ? (iii) If 100 plants are produced in progeny, then how many plants will show the recessive trait ?
(a) Variation refers to the subtle differences that exist between individuals of a species, even if they are born to the same parents.
Two main reasons for variation are:
- Small inaccuracies in DNA copying during cell division.
- The process of sexual reproduction, which maximizes the number of successful variations.
OR
(b) (i) In the progeny, all plants will have violet flowers because violet is the dominant trait.
(ii) In the progeny, approximately three-quarters () of the plants will have violet flowers and one-quarter () will have white flowers.
(iii) If 100 plants are produced, 25 plants will show the recessive trait (white flowers).
Marking Scheme
- 1Definition of variation (1 mark)
- 2Two reasons for variation (DNA copying errors and sexual reproduction) (1 mark)
- 3OR (b)(i) characteristics (0.5 marks)
- 4(b)(ii) observation (3:1 ratio) (1 mark)
- 5(b)(iii) Calculation of recessive plants (0.5 marks)
Hint
Recall Mendel's monohybrid cross where the generation shows only one parental trait, and the generation shows a ratio.
Quick Oral Answer
Variation is the difference in traits among individuals of the same species. It is caused by DNA copying errors and genetic recombination during sexual reproduction. In a monohybrid cross, the recessive trait is hidden in and expressed in of the population.
Analysis & Explanation
Variation is the basis of diversity in living organisms. In asexual reproduction, variations are minimal and arise only due to DNA copying errors. In sexual reproduction, variations are significantly higher due to the combination of genetic material from two parents. In Mendel's experiments, the generation always expresses the dominant trait (violet flowers), masking the recessive trait (white flowers). The recessive trait reappears in the generation in a ratio because the plants carry the 'factor' for the recessive trait even if they don't express it.
Common Mistakes
- 1Confusing the generation with the generation.
- 2Assuming variations only occur in sexual reproduction; they also occur in asexual reproduction but to a lesser extent.
Interesting Facts
Even in a field of sugarcane (asexual reproduction), very little variation is visible, whereas in humans, variations are quite distinct.
Spotted a mistake or something unclear?
Tell us — we fix reported answers fast.
Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2022?
This question carries 2 marks in the CBSE Class 10 Science 2022 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 "Accumulation of Variation during Reproduction" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2022 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2022 paper.