Heredity and Variation – Long Answer Questions (CBSE Class 10 Science, Biology)
Medium Level (Application & Explanation)
Q1. Explain the concept of heredity and how genes control traits, using simple agricultural examples.
Answer:
Heredity is the transfer of traits from parents to offspring through genes present on DNA. Each offspring gets one set of genes from the mother and one from the father.
These genes act like instructions, deciding features such as wheat grain color, flower color, plant height, or milk yield in cows.
In agriculture, if a cow breed is selected from parents with high milk yield, the calves are more likely to inherit this trait. Similarly, crossing pest-resistant rice with high-yield rice can result in a variety that has both qualities.
Genes may be visible in traits like color or invisible like disease resistance. Farmers and breeders use this knowledge to select parents and improve breeds.
Understanding heredity helps explain why offspring resemble parents but still show differences due to new gene combinations during reproduction.
Q2. Differentiate between inherited (genetic) and acquired (environmental) variation with examples from crops and livestock.
Answer:
Variation is the difference seen among individuals of the same species, and it is of two main types: inherited and acquired.
Inherited (genetic) variation comes from gene combinations passed from parents to offspring. Example: Some tomato plants in a field naturally resist pests better due to their genes.
Acquired (environmental) variation is caused by external factors like water, light, soil, and nutrition, and usually does not pass to the next generation. Example: Two rice plants from the same seed batch may grow to different heights because one got more sunlight.
In livestock, a cow may give more milk in one season due to better feed (acquired), but a breed known for high milk yield shows inherited variation.
Farmers use inherited variation to breed and select better varieties, while they manage acquired variation by improving farming practices like irrigation and fertilization.
Q3. Using wheat grain color as an example, explain how the combination of parental genes influences traits in the next generation.
Answer:
When two wheat varieties with different grain colors (e.g., red and white) are crossed, the grain color in the offspring depends on the genes each parent contributes.
If the red color trait is stronger (dominant) and the white color trait is weaker (recessive), the first generation (F1) may mostly show red grains.
In the next generation (F2), when F1 plants are allowed to self-pollinate, both red and white grains can reappear because gene combinations reshuffle.
This shows how heredity and gene recombination produce variation in traits across generations.
Farmers and breeders observe these patterns to select plants that show desired colors or other traits and continue breeding them to fix these characteristics over time.
The key idea: Parental gene combinations decide the visible traits in offspring, and recombination creates diversity within the crop.
Q4. Describe how hybrid crops (like rice) are produced to combine high yield with pest resistance. Explain the steps and their purpose.
Answer:
To create a hybrid crop that is both high-yielding and pest-resistant, breeders follow a step-by-step process:
Select Parent A with high yield and Parent B with pest resistance.
Perform a cross between A and B to produce F1 seeds.
Grow F1 plants and observe traits; many may show both qualities due to combined genes.
Select the best-performing plants and cross or self-pollinate them for several generations to stabilize (fix) the desirable traits.
Conduct field trials in different environments to confirm consistent performance.
This method uses heredity (passing traits via genes) and variation (different combinations appearing in offspring).
The final outcome is a new variety that gives better yield, saves pesticides, and increases profit for farmers.
Q5. What does the “bean seed variation” activity teach about variation? Explain its agricultural importance with reasons.
Answer:
In the bean seed activity, students collect seeds from the same plant and notice differences in size, shape, and color.
This shows that even seeds from a single parent display variation, due to gene recombination and sometimes small environmental effects.
The activity teaches that variation is natural and present in all living populations, even when individuals appear similar.
For agriculture, this is crucial because variation is the raw material for selection. Farmers can pick seeds from plants that showed better yield, better taste, or better resistance.
Over seasons, selecting the best seeds helps gradually improve the crop.
It also highlights why farmers should avoid using only one type forever; maintaining diversity helps crops adapt to changing conditions like pests or drought.
High Complexity (Analytical & Scenario-Based)
Q6. A farmer finds uneven yield among wheat plants grown from the same seed lot. Analyze the possible reasons (genetic vs environmental) and propose a plan to improve average yield.
Answer:
Uneven yield can arise from:
Genetic variation: Even in a seed lot, seeds may carry slightly different gene combinations leading to natural differences in growth and yield.
Environmental variation: Differences in soil fertility, water availability, sunlight, spacing, or pest pressure cause uneven performance.
Action plan:
Conduct a controlled trial: Grow plants with uniform spacing, equal irrigation, and similar fertilizer to reduce environmental differences.
Identify plants that consistently give high yield across two to three seasons; save their seeds for the next crop (selection for inherited traits).
Improve field practices: Soil testing, balanced fertilization, mulching, and integrated pest management to reduce environmental stress.
Consider using a hybrid variety known for stable yield.
By combining better agronomy (managing environment) with seed selection (using heredity), the farmer can raise the average yield and reduce variability.
Q7. Design a multi-season breeding plan to develop rice that is both high-yielding and drought-tolerant. Include selection, testing, and maintaining diversity.
Answer:
Step 1: Choose Parent A (high yield) and Parent B (drought tolerance). Verify traits in small plots.
Step 2: Make controlled crosses to produce F1 seeds. Grow F1 and note plants showing both traits.
Step 3: Advance to F2 and F3 generations by selfing; observe segregation and select top plants under both normal and low-water conditions.
Step 4: Conduct replicated field trials across multiple locations and seasons to test for consistency.
Step 5: Keep a seed reserve of diverse lines to avoid losing genetic variation; maintain a few backup lines as alternatives.
Step 6: Use data-based selection: yield per area, days to maturity, survival under drought, and pest incidence.
Step 7: After stabilization, multiply best lines and share with farmers for on-farm trials.
This plan uses heredity for trait transfer, variation for discovering the best combinations, and diversity for long-term stability.
Q8. In livestock breeding, selecting only for high milk yield led to cows that fall ill more often. Analyze this trade-off and propose a balanced selection strategy.
Answer:
The issue shows a trade-off: focusing on a single trait (high milk yield) may unintentionally reduce disease resistance or overall fitness.
Reasons:
Reduced genetic diversity when only a few high-yield animals contribute to the next generation.
Possible negative correlations between yield and immunity or body condition.
Balanced strategy:
Use multi-trait selection: include milk yield, disease resistance, fertility, and longevity in the breeding goal.
Keep records and select animals that perform well overall, not just in milk yield.
Improve the environment: nutrition, hygiene, vaccination, and stress-free housing to support health (managing acquired variation).
Maintain genetic diversity by using multiple sires or bull lines and avoiding close inbreeding.
Evaluate performance across seasons to confirm stable traits.
This approach balances productivity with health, using both heredity and management to achieve sustainable outcomes.
Q9. After a pest attack, only some tomato plants survive. Design an experiment to test whether pest resistance is inherited or environmental. State controls, steps, and expected results.
Answer:
Steps:
Collect seeds from survivor plants (putative resistant) and from non-survivors’ sibling plants if available.
Grow both seed sets in a controlled environment with the same soil, water, and light.
Expose both groups to the same pest pressure or plant them in a field with uniform pest incidence.
Controls:
Include a known susceptible variety and a known resistant variety as controls.
Keep a set with no pest exposure to ensure general plant health.
Observations:
If the progeny of survivors consistently show higher survival and less damage under identical ...
