CBSE Class 10 Science (2026–27)
Chapter 8: Heredity and Evolution
20 Important Questions and Answers
1. What is heredity? Explain its importance.
Answer:
Heredity is the process by which characteristics are passed from parents to their offspring through genes. It ensures continuity of life by transferring biological information from one generation to the next. Traits such as eye colour, hair type, height, and blood group are inherited through heredity. It plays an important role in maintaining similarities among members of the same species. At the same time, heredity also allows slight variations to occur, which help organisms adapt to changing environments. These variations contribute to evolution over long periods. Thus, heredity is essential for both the preservation of species characteristics and the development of biodiversity through evolutionary changes.
2. What are inherited traits and acquired traits? Give examples.
Answer:
Inherited traits are characteristics that are passed from parents to offspring through genes. These traits are present in the DNA and can be transferred from one generation to another. Examples include blood group, eye colour, and natural hair texture. Acquired traits are characteristics developed during an individual’s lifetime due to environmental influences, habits, or experiences. These traits are not controlled by genes and therefore cannot be inherited. Examples include muscular body development through exercise, scars from injuries, or language skills learned during life. Since acquired traits do not affect the DNA of reproductive cells, they are not passed on to offspring, unlike inherited traits.
3. Explain the role of genes in heredity.
Answer:
Genes are the basic units of heredity present on chromosomes inside the nucleus of cells. They contain DNA, which carries instructions for the development and functioning of an organism. Genes determine inherited traits such as height, eye colour, and blood group. During reproduction, genes are passed from parents to offspring through reproductive cells. Each offspring receives a combination of genes from both parents, resulting in similarities as well as differences. Genes also influence the production of proteins, which control various body functions and characteristics. Therefore, genes play a vital role in transmitting hereditary information and maintaining continuity of traits across generations.
4. What is variation? Why is it important?
Answer:
Variation refers to the differences in characteristics among individuals of the same species. These differences may occur in physical appearance, behaviour, or genetic makeup. Variations arise due to genetic recombination, mutations, and environmental influences. They are important because they help organisms adapt to changing environmental conditions. If all individuals were identical, a sudden environmental change could wipe out an entire species. Variations increase the chances that some individuals will survive and reproduce under new conditions. Over time, useful variations accumulate and contribute to evolution. Thus, variation is essential for the survival, adaptation, and long-term evolution of species.
5. Differentiate between dominant and recessive traits.
Answer:
Dominant traits are those that express themselves even when only one copy of the gene is present. Recessive traits are expressed only when both copies of the gene are recessive. In a pair of contrasting traits, the dominant trait masks the expression of the recessive trait. For example, in pea plants, tallness (T) is dominant over dwarfness (t). A plant with genotype TT or Tt will be tall, while only tt will be dwarf. Dominant traits are represented by capital letters, whereas recessive traits are represented by small letters. Understanding dominant and recessive traits helps explain inheritance patterns observed by Mendel.
6. State Mendel’s Law of Dominance.
Answer:
Mendel’s Law of Dominance states that when two contrasting traits are present together in an organism, only one trait is expressed while the other remains hidden. The expressed trait is called the dominant trait, and the hidden trait is called the recessive trait. Mendel observed this law through experiments on pea plants. For example, when a tall plant was crossed with a dwarf plant, all offspring in the first generation were tall. This showed that the trait for tallness dominated over dwarfness. The law explains why certain traits appear in offspring even when contrasting traits are inherited from both parents.
7. Explain Mendel’s monohybrid cross experiment.
Answer:
Mendel performed a monohybrid cross by crossing a pure tall pea plant (TT) with a pure dwarf pea plant (tt). In the first filial generation (F₁), all offspring were tall (Tt), showing that tallness is dominant. When these F₁ plants were self-pollinated, the second filial generation (F₂) produced both tall and dwarf plants in a ratio of 3:1. This experiment demonstrated that traits are inherited as separate units and that recessive traits can reappear in later generations. The monohybrid cross provided evidence for the Law of Dominance and the Law of Segregation, forming the basis of modern genetics.
8. What is the significance of sexual reproduction in evolution?
Answer:
Sexual reproduction involves the fusion of male and female gametes, resulting in offspring with a combination of genes from both parents. This process creates genetic variation among individuals. Such variations increase the adaptability of a population to changing environmental conditions. Some variations may provide survival advantages, helping organisms resist diseases, obtain food more effectively, or survive environmental changes. Over many generations, these beneficial variations accumulate and contribute to evolution. Sexual reproduction therefore plays a major role in producing diversity within species and provides the raw material on which natural selection acts, leading to the development of new species.
9. Why are variations more common in sexually reproducing organisms?
Answer:
Variations are more common in sexually reproducing organisms because genetic material from two parents combines during reproduction. During the formation of gametes, crossing over and recombination occur, creating new gene combinations. At fertilization, male and female gametes unite randomly, producing offspring with unique genetic characteristics. In contrast, asexual reproduction involves only one parent and produces genetically identical offspring except for occasional mutations. The greater genetic diversity produced through sexual reproduction increases the chances of survival in changing environments. Therefore, sexually reproducing organisms show a higher degree of variation, which plays an important role in adaptation and evolution.
10. What are fossils? How do they help in studying evolution?
Answer:
Fossils are the preserved remains, impressions, or traces of ancient organisms found in rocks. They provide direct evidence of organisms that lived millions of years ago. Fossils help scientists understand the evolutionary history of life on Earth by showing how species have changed over time. By studying fossils from different geological layers, scientists can determine the age of organisms and trace evolutionary relationships. Fossils reveal extinct species and transitional forms that connect ancient and modern organisms. They also provide information about past environments and climatic conditions. Therefore, fossils are important tools for studying the process of evolution.
11. Explain the process of fossil formation.
Answer:
Fossil formation begins when an organism dies and is quickly buried under layers of mud, sand, or sediment. Over time, soft body parts decay while hard parts such as bones, shells, or teeth remain. Additional layers of sediment accumulate above the remains, creating pressure. Minerals gradually replace the original tissues, turning them into rock-like structures. This process may take millions of years. Sometimes, impressions or footprints are also preserved as fossils. Geological movements may later expose these fossils at the Earth’s surface. Fossils provide valuable evidence about ancient life forms and help scientists understand evolutionary changes.
12. What is natural selection?
Answer:
Natural selection is the process through which organisms with favourable traits survive and reproduce more successfully than others. It was proposed by the naturalist Charles Darwin. According to this theory, individuals within a population show variations. Those with advantageous variations are better adapted to their environment and are more likely to survive, reproduce, and pass these traits to future generations. Less adapted individuals may not survive or reproduce effectively. Over many generations, beneficial traits become more common in the population. Natural selection is one of the main mechanisms responsible for evolution and the formation of new species.
13. Explain Darwin’s theory of evolution.
Answer:
Darwin’s theory of evolution is based on natural selection. He observed that organisms produce more offspring than can survive, leading to competition for resources. Individuals within a population show variations, and some variations provide advantages in survival and reproduction. Organisms with favourable traits are naturally selected and leave more offspring. These advantageous traits are passed to future generations and gradually become common. Over long periods, the accumulation of beneficial variations can result in the formation of new species. Darwin explained evolution as a gradual process driven by natural selection. His theory remains one of the most important foundations of modern biology.
14. What are homologous organs? Give examples.
Answer:
Homologous organs are organs that have a common evolutionary origin and similar basic structure but may perform different functions. These organs indicate that different organisms evolved from a common ancestor. A common example is the forelimbs of humans, whales, bats, and horses. Although these limbs perform different functions such as grasping, swimming, flying, and running, they have a similar bone arrangement. The presence of homologous organs provides strong evidence for evolution because it shows how the same basic structure has been modified over time to suit different environmental needs. Thus, homologous organs support the idea of common ancestry.
15. What are analogous organs? Give examples.
Answer:
Analogous organs are organs that perform similar functions but differ in their structure and evolutionary origin. These organs develop independently in different organisms as adaptations to similar environmental conditions. An example is the wings of birds and insects. Both are used for flying, but their structures and origins are completely different. Bird wings are modified forelimbs with bones, whereas insect wings are extensions of the exoskeleton. Analogous organs provide evidence for convergent evolution, where unrelated organisms develop similar adaptations. They show that similar environmental pressures can lead to the development of similar functional structures in different species.
16. Differentiate between homologous and analogous organs.
Answer:
Homologous organs have a common evolutionary origin and similar internal structure but perform different functions. Examples include the forelimbs of humans, bats, and whales. Analogous organs, on the other hand, perform similar functions but have different structures and evolutionary origins. Examples include the wings of birds and insects. Homologous organs indicate divergent evolution, where related organisms adapt to different environments. Analogous organs indicate convergent evolution, where unrelated organisms develop similar adaptations due to similar environmental conditions. Both types of organs provide important evidence for evolution and help scientists understand relationships among different organisms.
17. What is speciation?
Answer:
Speciation is the process by which new species are formed from existing populations. It occurs when groups of the same species become isolated and gradually develop significant genetic differences. Isolation may be geographical, ecological, or reproductive. Over time, variations accumulate due to mutations, natural selection, and genetic drift. These changes may become so great that the separated groups can no longer interbreed and produce fertile offspring. At this stage, a new species is formed. Speciation is an important outcome of evolution because it increases biodiversity and leads to the development of different forms of life adapted to various environments.
18. What factors lead to speciation?
Answer:
Several factors contribute to speciation. Geographical isolation separates populations by physical barriers such as mountains, rivers, or oceans. Genetic variations arise through mutations and recombination during reproduction. Natural selection favours advantageous traits in different environments. Genetic drift can also change gene frequencies, especially in small populations. Reproductive isolation prevents interbreeding between populations. Over time, these factors cause significant genetic differences to accumulate. Eventually, the separated populations become distinct species that cannot produce fertile offspring together. Thus, isolation, variation, natural selection, and reproductive barriers are the major factors responsible for the formation of new species.
19. How does evolution explain the diversity of life on Earth?
Answer:
Evolution explains that all living organisms share common ancestors and have changed gradually over millions of years. Genetic variations arise naturally within populations. Environmental conditions and natural selection favour certain variations that improve survival and reproduction. As these favourable traits accumulate, populations adapt to different habitats and lifestyles. Over long periods, new species form through speciation. This continuous process has produced the vast diversity of plants, animals, and microorganisms found today. Evolution shows how simple ancestral forms gave rise to complex organisms. Therefore, it provides a scientific explanation for the rich variety of life on Earth.
20. Why is studying evolution important?
Answer:
Studying evolution helps us understand the origin, development, and relationships among living organisms. It explains how species adapt to changing environments and how new species arise. Knowledge of evolution is useful in medicine for understanding antibiotic resistance and the spread of diseases. It also helps in agriculture by improving crop and animal breeding programs. Evolutionary studies provide evidence for biodiversity and conservation efforts by identifying relationships among species. Understanding evolution allows scientists to predict biological changes and solve practical problems. Therefore, evolution is a fundamental concept that connects all branches of biology and enhances our understanding of life.