Looking for reliable SEBA Class 10 Science Chapter 9 (Heredity and Evolution) extra questions and answers for the 2026–27 academic year? Access important short questions, conceptual explanations on Mendel’s crosses, sex determination mechanisms, and previous year HSLC practice notes to score top marks.
EXTRA QUESTION AND ANSWER
Q1. What is variation and why is it important for a species?
Answer: Variation refers to the differences in traits and characteristics observed among individual organisms of the same species. It is essential because it enables species to adapt to changing environmental conditions, prevents mass extinction during drastic changes, and forms the basis for natural selection and evolution.
Q2. How does the degree of variation differ between asexual and sexual reproduction?
Answer: Asexual reproduction produces minimal variation because offspring inherit DNA from a single parent, with differences arising solely due to minor DNA copying errors. Sexual reproduction creates significantly higher variation through the random combination and shuffling of genetic material from two distinct parents during gamete formation.
Q3. Define the term heredity.
Answer: Heredity is the transmission of physical or biological traits, characteristics, and genetic information from parents to their offspring through sexual or asexual reproduction.
Q4. Who is known as the “Father of Genetics” and why?
Answer: Gregor Johann Mendel is known as the Father of Genetics because he conducted pioneering hybridization experiments on garden pea plants (Pisum sativum) and formulated the fundamental laws governing genetic inheritance.
Q5. What were the primary observations and conclusions of Mendel’s monohybrid cross?
Answer: When Mendel crossed a pure-bred tall pea plant (TT) with a pure-bred dwarf pea plant (tt):
- F1 Generation: All offspring were tall (Tt).
- F2 Generation: Self-pollination of F1 plants produced tall and dwarf plants in a 3:1 phenotypic ratio.
- Conclusion: The allele for tallness (T) is dominant over the allele for shortness (t), which remains recessive.
SEBA Class 10 Science Chapter 9 Extra Questions
Q6. What principle did Mendel’s dihybrid cross demonstrate?
Answer: Mendel’s dihybrid cross demonstrated the Law of Independent Assortment. By tracking two contrasting traits simultaneously (such as seed color and seed shape), he observed a 9:3:3:1 phenotypic ratio in the F2 generation, proving that alleles for different traits segregate independently during gamete formation.
Q7. Define dominant and recessive traits with a suitable example for each.
Answer:
- Dominant Trait: A genetic trait that expresses itself in the presence of even a single copy of its allele (e.g., the allele for tallness, T, in pea plants).
- Recessive Trait: A genetic trait that is masked in the presence of a dominant allele and expresses itself only when two identical copies are present (e.g., the allele for shortness, t, in pea plants).
Q8. What are genes and what function do they perform in living organisms?
Answer: Genes are functional segments of DNA located on chromosomes that serve as the basic physical units of heredity. They function by encoding instructions to synthesize specific proteins that control the expression of physical and physiological traits in an organism.
Q9. Explain how a gene controls and expresses a trait like tallness in pea plants.
Answer: A gene contains the genetic code to produce a specific enzyme responsible for synthesizing plant growth hormones. An efficient gene produces a fully functional enzyme that yields sufficient hormone, resulting in a tall plant. If the gene is altered or defective, less efficient enzymes are produced, leading to lower hormone levels and a short plant.
Q10. What are chromosomes and how many pairs of chromosomes are present in human somatic cells?
Answer: Chromosomes are thread-like structures composed of tightly coiled DNA and proteins located inside the cell nucleus, carrying hereditary information in the form of genes. Human somatic (body) cells contain 23 pairs of chromosomes (46 chromosomes in total).
Class 10 Science Chapter 9 Important Questions SEBA 2026-27
Q11. How is the sex of a child determined in human beings?
Answer: Females produce eggs carrying only X chromosomes, while males produce sperm carrying either an X or a Y chromosome. During fertilization:
- If an X-bearing sperm fertilizes the egg, the child will be female (XX).
- If a Y-bearing sperm fertilizes the egg, the child will be male (XY). Therefore, the genetic contribution of the father determines the sex of the child.
Q12. Why is the mother not responsible for determining the sex of the baby?
Answer: Human females are homogametic, meaning all egg cells carry a single X chromosome. Human males are heterogametic, producing sperm with either an X or a Y chromosome. Since the egg contributes an X chromosome in every case, it is the father’s sperm that introduces the X or Y chromosome to determine the child’s sex.
Q13. Define the term evolution.
Answer: Evolution is the gradual, directional change in the inherited characteristics and genetic makeup of biological populations over successive generations, leading to the origin of new traits and species.
Q14. What are the primary factors that drive the process of evolution?
Answer: Evolution is primarily driven by three factors:
- Genetic variations arising from sexual reproduction and DNA copying errors.
- Natural selection, which favors beneficial adaptations.
- Genetic drift, which causes random changes in gene frequencies in small populations.
Q15. Explain the concept of natural selection using the example of a beetle population.
Answer: In a population of red beetles living on green leaves, a genetic variation produces a green beetle. Crows easily spot and eat red beetles, while green beetles remain camouflaged on the leaves. As a result, more green beetles survive and reproduce, gradually turning the majority of the beetle population green through natural selection.
Q16. What is genetic drift and which type of population is most affected by it?
Answer: Genetic drift is the random change in the frequency of alleles within a population due to chance events rather than natural selection. It has a significantly greater impact on small populations, where accidental events can eliminate specific traits regardless of their survival advantage.
Q17. Why is weight loss in beetles due to food scarcity not considered an evolutionary change?
Answer: Weight loss is an acquired trait caused by environmental factors. It alters only body (somatic) tissues without changing the DNA sequence of germ cells (gametes). Because non-genetic changes cannot be inherited by future generations, they do not contribute to evolution.
Q18. Differentiate between inherited traits and acquired traits with examples.
Answer:
| Trait Type | Description | Inherited by Offspring? | Example |
| Inherited Trait | Traits controlled by DNA that are passed from parents to offspring. | Yes | Eye color, blood group |
| Acquired Trait | Traits developed during an individual’s lifetime due to environment or practice. | No | Learning to swim, weight loss |
Q19. Why do only inherited traits contribute to the evolutionary process?
Answer: Only inherited traits are encoded in the DNA sequence of germ cells (sperm and egg). Since natural selection operates on genetic information passed across generations, non-heritable traits that do not alter gametic DNA cannot influence evolutionary change.
Q20. Summarize Charles Darwin’s theory of natural selection.
Answer: Darwin’s theory states that organisms produce more offspring than can survive, creating competition for resources. Individuals with favorable variations better suited to their environment survive, reproduce, and pass these advantageous traits to their offspring. Over generations, these successful traits accumulate, leading to the adaptation of populations and the formation of new species.
Heredity and Evolution Class 10 SEBA Extra Question Answer
Q21. What was the contribution of J.B.S. Haldane to the theory of the origin of life?
Answer: J.B.S. Haldane suggested that life originated from simple inorganic molecules present on early Earth. He hypothesized that early atmospheric conditions provided the energy needed to form complex organic compounds essential for life.
Q22. Describe the Miller–Urey experiment and its significance.
Answer: Stanley Miller and Harold Urey simulated early Earth’s atmosphere using methane, ammonia, hydrogen, and water vapor, passing electric sparks to mimic lightning. After a week, simple organic molecules including amino acids were formed, proving that life’s building blocks could arise spontaneously from non-living matter.
Q23. Define the term speciation.
Answer: Speciation is the evolutionary process by which a new, distinct species arises from an existing population when groups become reproductively isolated and can no longer interbreed to produce fertile offspring.
Q24. List three major factors that contribute to the process of speciation.
Answer: Three major factors responsible for speciation are:
- Geographical isolation (physical barriers separating populations)
- Genetic drift (random changes in gene frequencies)
- Natural selection (environmental pressures favoring beneficial adaptations)
Q25. Explain with an example how geographical isolation can lead to speciation.
Answer: If a population of beetles is divided by a physical barrier like a river or mountain, the isolated groups stop interbreeding. Over generations, distinct genetic variations, natural selection, and genetic drift accumulate independently in each group until they become so genetically different that they can no longer interbreed, forming two separate species.
SEBA Class 10 Science Chapter 9 Notes
Q26. How are evolution and classification interlinked?
Answer: Classification involves grouping organisms based on shared similarities and traits. Organisms that share more characteristics are closely related and share a recent common ancestor, making biological classification a direct reflection of evolutionary relationships.
Q27. Define homologous organs with two suitable examples.
Answer: Homologous organs are anatomical structures in different organisms that share a similar basic internal structure and evolutionary origin, but perform different functions.
Examples:
- Forelimbs of humans and wings of bats
- Forelimbs of whales and legs of dogs
Q28. Define analogous organs with two suitable examples.
Answer: Analogous organs are structures in different organisms that perform similar functions but possess completely different basic anatomical structures and evolutionary origins.
Examples:
- Wings of birds and wings of butterflies
- Flippers of penguins and flippers of dolphins
Q29. What are fossils and how are they formed?
Answer: Fossils are the preserved remains, impressions, or traces of ancient organisms found in Earth’s crust. They form when dead organisms are buried in sediment, mud, or silt, and over millions of years, the organic matter is mineralized and turned into rock under high pressure.
Q30. How do fossils help in studying evolutionary history?
Answer: Fossils provide direct physical evidence of past life forms. By dating rock layers and examining fossilized structures, scientists can trace structural changes over time, establish temporal timelines, and identify transitional links between extinct simple ancestors and complex modern species.
HSLC Science Chapter 9 Important Short Questions
Q31. Explain how complex organs, such as the eye, evolved gradually over time.
Answer: Complex organs like the eye did not form instantly, but evolved through small, incremental changes over generations. It started as a simple light-sensitive spot in unicellular organisms (like Planaria), which gradually deepened into a cup-shaped structure, eventually adding a flexible lens and retina. Each intermediate stage provided a distinct survival advantage selected by natural selection.
Q32. Describe how feathers evolved and adapted for different functions.
Answer: Feathers initially evolved in certain ancient reptiles (dinosaurs) to provide thermal insulation against cold weather. Later in evolution, birds adapted these existing feather structures for flight, demonstrating that traits evolved for one function can be repurposed for a new evolutionary purpose.
Q33. What is artificial selection? Explain using wild cabbage as an example.
Answer: Artificial selection is the intentional breeding of plants or animals by humans to preserve and amplify specific desirable traits.
Example: From a single wild cabbage ancestor (Brassica oleracea), farmers selectively bred different traits over centuries, creating distinct modern vegetables:
- Selection for short distances between leaves -> Cabbage
- Selection for arrested flower development -> Broccoli
- Selection for sterile flowers -> Cauliflower
- Selection for swollen stems -> Kohlrabi
- Selection for larger leaves -> Kale
Q34. What is molecular phylogeny and how does it determine evolutionary relationships?
Answer: Molecular phylogeny is the study of evolutionary relationships among organisms by analyzing and comparing their cellular structures and DNA sequences. Organisms with a higher percentage of identical DNA sequences share a more recent common ancestor.
Q35. Why is evolution not considered equivalent to biological progress?
Answer: Evolution produces adaptation to specific local environments rather than absolute structural improvement or progress. Simple organisms like bacteria have survived successfully for billions of years without growing more complex; therefore, evolution creates diversity and specialization rather than “higher” or “lower” species.
🔬 Updated Extra Questions Guide Notice: This page features an extensive collection of SEBA Class 10 Science Chapter 9 (Heredity and Evolution) Extra Questions and Detailed Answers updated for the 2026–27 academic session. All conceptual notes, cross diagrams, and genetics explanations strictly follow the latest revised Assam Board (SEBA) curriculum.
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