Looking for accurate SEBA Class 10 Science Chapter 9 (Heredity and Evolution) textual solutions for the 2026–27 academic year? Access step-by-step textbook exercise answers, Mendel’s inheritance law explanations, monohybrid/dihybrid cross ratios, and sex determination notes designed to help you score top marks in your HSLC board exams.
Blue question
Q1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer: Trait B is likely to have arisen earlier because asexual reproduction involves minimal genetic variation. Therefore, traits present in a higher percentage of the population have been passed down through more generations.
Q2. How does the creation of variations in a species promote survival?
Answer: Variations provide certain individuals with favorable adaptations to withstand environmental changes, such as temperature fluctuations or disease, thereby preventing the extinction of the species.
Q3. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer: When Mendel crossed pure-bred tall pea plants with pure-bred dwarf pea plants, all F1 offspring were tall. When F1 plants self-pollinated, the dwarf trait reappeared in the F2 generation in a 3:1 ratio, proving that the tall trait is dominant and the dwarf trait is recessive.
Q4. How do Mendel’s experiments show that traits are inherited independently?
Answer: In a dihybrid cross involving two distinct traits (such as round yellow seeds and wrinkled green seeds), Mendel obtained new combinations in the F2 generation in a 9:3:3:1 ratio. This demonstrated that alleles for different traits segregate independently during gamete formation.
Q5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
Answer: No, this information alone is insufficient. Blood group O is recessive , and the daughter can inherit an allele from her mother and another i allele from a heterozygous father, making it impossible to determine dominance without knowing the father’s genotype.
SEBA Class 10 Science Chapter 9 Solutions
Q6. How is the sex of the child determined in human beings?
Answer: Sex is determined by the father’s sperm cell during fertilization. Females carry two X chromosomes (XX), while males carry one X and one Y chromosome (XY). If a sperm carrying an X chromosome fertilizes the egg, the child will be female (XX); if a sperm carrying a Y chromosome fertilizes the egg, the child will be male (XY).
Q7. What are the different ways in which individuals with a particular trait may increase in a population?
Answer: A particular trait can increase in a population through natural selection (providing a survival advantage), genetic drift (accidental changes in gene frequency), or artificial selection (selective breeding by humans).
Q8. Why are traits acquired during the lifetime of an individual not inherited?
Answer: Acquired traits cause changes only in non-reproductive somatic tissues and do not alter the DNA sequence within germ cells (gametes). Therefore, they cannot be transmitted to offspring.
Q9. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer: A small population reduces genetic diversity, leading to inbreeding depression, accumulation of harmful recessive mutations, and decreased adaptability to environmental changes or diseases, which increases the risk of extinction.
Q10. What factors could lead to the rise of a new species (speciation)?
Answer: Speciation can occur due to geographical isolation, reproductive isolation, natural selection, and genetic drift, which together lead to significant genetic divergence over time.
Class 10 Science Chapter 9 Question Answer SEBA 2026-27SEBA Class 10 Science Chapter 9 Numericals
Q11. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer: No, geographical isolation is not a major factor in the speciation of self-pollinating plants because self-pollination occurs within the same flower or plant. They do not rely on gene flow from other populations, so physical separation does not alter their reproductive process.
Q12. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer: No, geographical isolation is not a major factor in asexually reproducing organisms because offspring are produced by a single parent without the fusion of gametes. Since gene flow between individuals does not occur, physical separation does not drive genetic divergence in the same way it does in sexually reproducing species.
Q13. Give an example of characteristics used to determine how close two species are in evolutionary terms.
Answer: Homologous organs, such as the forelimbs of humans, bats, and whales, serve as an example. Although modified for different functions like grasping, flying, and swimming, they share the same basic anatomical bone structure, indicating that these species derived from a common ancestor.
Q14. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer: No, the wing of a butterfly and the wing of a bat are analogous organs, not homologous organs. Although both perform the function of flight, they have entirely different structural frameworks and evolutionary origins—the butterfly wing is an extension of the integument, while the bat wing consists of skin folds stretched over elongated finger bones.
Q15. What are fossils? What do they tell us about the process of evolution?
Answer: Fossils are the preserved remains, impressions, or traces of organisms that lived in the geological past. They provide direct structural evidence of ancient life forms, help trace evolutionary lineages, establish temporal relationships between species, and show how complex organisms gradually evolved from simpler ancestors over time.
Heredity and Evolution Class 10 SEBA Textual Exercise Solutions
Q16. Why are human beings who look so different from each other in terms of size, color, and appearance said to belong to the same species?
Answer: Human beings belong to the same species (Homo sapiens) because they share a common genetic blueprint and can freely interbreed with one another to produce fertile offspring. Superficial differences such as skin color, height, and facial features are minor geographical variations that do not create reproductive barriers.
Q17. In evolutionary terms, can we say which among bacteria, spiders, fish, and chimpanzees have a ‘better’ body design? Why or why not?
Answer: No, we cannot classify any of these organisms as having a “better” body design. Evolution produces adaptation rather than perfection; each of these organisms possesses a body design well-suited to survive, adapt, and reproduce effectively within its specific ecological niche.
Exercise
Q1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. Which of the following depicts the genetic makeup of the tall parent?
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Answer: (c) TtWW
Explanation: All offspring had violet flowers, which means the tall parent must carry two dominant alleles for flower color (WW). Since nearly half of the offspring were short, the tall parent must carry one recessive allele for height (Tt). Therefore, the correct genotype is TtWW.
Q2. Which of the following is an example of homologous organs?
(a) Our arm and a dog’s foreleg
(b) Our teeth and an elephant’s tusks
(c) Potato and runners of grass
(d) All of the above
Answer: (d) All of the above
Explanation: All these pairs have a similar basic anatomical structure and origin but perform different functions. This shared structural design indicates that they originated from a common evolutionary ancestor.
Q3. In evolutionary terms, which of the following do human beings have the most in common with?
(a) A Chinese schoolboy
(b) A chimpanzee
(c) A spider
(d) A bacterium
Answer: (a) A Chinese schoolboy
Explanation: All human beings belong to the exact same species (Homo sapiens). Therefore, humans share maximum genetic similarity and common evolutionary traits with each other compared to any other living organism.
Q4. A study found that children with light-colored eyes are likely to have parents with light-colored eyes. Based on this information, can you state whether the light eye color trait is dominant or recessive? Why or why not?
Answer: No, this information is not sufficient to determine whether light eye color is dominant or recessive. We need data from multiple generations or a cross between contrasting traits to identify which allele masks the other.
Q5. How are the areas of study—evolution and classification—interlinked with each other?
Answer: Classification involves grouping organisms based on their shared characteristics. Organisms that share more traits are closely related and share a recent common ancestor, which directly reflects their evolutionary history.
SEBA Class 10 Science Chapter 9 NotesClass 10 Science Chapter 9 Question Answer SEBA 2026-27
Q6. Explain the terms homologous organs and analogous organs with one suitable example for each.
Answer:
- Homologous Organs: Organs that have a similar basic structure and evolutionary origin but perform different functions.
Example: The forelimbs of a human and a bat.
- Analogous Organs: Organs that perform the same function but have completely different structures and origins.
Example: The wings of a butterfly and a bat.
Q7. Outline a simple experiment or project to determine the dominant coat color in dogs.
Answer:
- Select a pure-bred dog with a black coat and another pure-bred dog with a brown coat.
- Cross them to obtain the first generation (F1) puppies.
- Observe the coat color of the F1 puppies. If all puppies are born with black coats, then black coat color is the dominant trait, and brown is the recessive trait.
Q8. Explain the importance of fossils in determining evolutionary relationships among organisms.
Answer: Fossils are the preserved remains or traces of ancient organisms. They provide direct physical evidence of past life, allow us to trace structural changes in organisms over time, and help establish links between simple extinct ancestors and modern complex species.
Q9. What experimental evidence do we have to support the theory that life originated from inanimate (non-living) matter?
Answer: The Stanley Miller and Harold Urey experiment provides evidence. They created conditions similar to early Earth in a laboratory and passed electrical sparks through simple gases like methane, ammonia, and hydrogen. This process produced amino acids, showing that complex organic molecules necessary for life could form from non-living chemicals.
Q10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this influence evolution?
Answer:
- Why Sexual Reproduction Gives More Variation: Sexual reproduction involves the combination of genetic material from two distinct parents and random shuffling of genes during gamete formation, whereas asexual reproduction produces identical offspring with minimal variations.
- Effect on Evolution: These unique genetic variations help organisms adapt better to changing environmental conditions, aiding survival and driving the process of natural selection and evolution.
HSLC Science Chapter 9 Question Answer
Q11. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer: Each human cell contains 23 pairs of chromosomes. During gamete formation (meiosis), the chromosome number is halved, producing sperm and egg cells that each contain 23 single chromosomes. When fertilisation occurs, the sperm cell from the father and the egg cell from the mother fuse to restore the original set of 46 chromosomes (23 pairs) in the zygote. This ensures that both male and female parents contribute an equal amount of genetic material to the offspring.
Q12. “Only variations that confer an advantage to an individual organism will survive in a population.” Do you agree with this statement? Why or why not?
Answer: No, I do not entirely agree with this statement. While advantageous variations are favored by natural selection because they aid survival, neutral variations that neither help nor harm an organism can also persist and survive in a population through genetic drift or accidental events.
🔬 Updated Solutions Notice: This page features complete, step-by-step SEBA Class 10 Science Chapter 9 (Heredity and Evolution) Textual Exercise Solutions updated for the 2026–27 academic session. All genetics ratios, dominant vs. recessive trait explanations, and evolutionary principles strictly follow the latest revised Assam Board (SEBA) textbook.
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