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8. Heredity

Text-book Questions

Text-book Questions

Page no. 143

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?

Ans: The trait which was presented in previous generation will remain same under asexual reproduction, but there shall be some differences. Similarly, the trait which exists in more percentage, it must be presented in before. So trait B which exists in 60 % probably it likely to have arisen earlier.  

Q2. How does the creation of variations in a species promote survival?

Ans: The species receive variation from their parents, while some variations are special in them, however which makes them special in nature. Different individuals in a species due to these differences may get advantages. Their survival will be fixed by nature to have accordingly variations. 

Page no. 147

Q1. How do Mendel’s experiments show that traits may be dominant or recessive?

Ans: According to Mendal's experiments, He selected two traits of pea which was tall pea plants and other was short pea plants as parents plants. In F₁ generation all plants were tall, but in second generation called F₂ three forth of pea plants were tall and one third were short. Both TT and Tt plants were tall while tt plants were only short, this experiments show that both traits were inherited but T trait for tallness was dominant and t trait for shortness was recessive. 

Q2. How do Mendel’s experiments show that traits are inherited
independently?

Ans: In Mendal's experiments show that all plants were tall in F₁ generation. No one was short, while parents were taken both tall and short plants of traits. Surprisingly, There were one third plants were short. This shows that traits are inherited independently.

Q3. 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?

Ans: Blood group O is dominant. The trait which appears is dominant in two trait blood group A and O. 

Q4. How is the sex of the child determined in human beings?

Ans: Sex chromosomes determines the sex in human being, in which there is only one pair sex chromosomes in human being. The males have XY chromosomes and the females have XX chromosomes. All children get X chromosome from their mother. So that is clear mother is no responsible for boy or girl. But Only Y chromosome of father determines sex of baby that will be boy or girl. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.

Page no. 150

Q1. What are the different ways in which individuals with a particular trait may increase in a population?

Ans: 

(i) Using sexual reproduction which provide large numbers of variation. 

(ii) However changing in colour prevent species like beetals. 

(iii) Small species may be victims, so there is great possibility to survive a large species. 

Q2. Why are traits acquired during the life-time of an individual not inherited?

Ans: Dominant traits transfer from one generation to other generation by DNA. An individual do not use sexual reproduction. So This has no special reproductive cells to reproduce. Hence, the trait transfer to DNA through reproductive cells. So there is no chance to inherit aquired trait over generation. Therefore the experiences of an individual during its lifetime cannot
be passed on to its progeny.  

Q3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Ans: Any individual evolutes when this produces changes. Changes bring variations and variations are responsible for their survival. But tiger have no made so much changes in their species. This causes small number of tigers a cause of worry from the point of view of genetics. 

Page no. 151 

Q1. What factors could lead to the rise of a new species?

Ans: (i) Genetic drift and natural selection affect the variations and they become too much differ.  

(ii) Changing in Chromosomes causes the germ cells of the two groups cannot fuse with each other.. 

(iii) Changing in DNA . 

Q2. Will geographical isolation be a major factor in the speciation of a selfpollinating plant species? Why or why not?

Ans: Physical features are affected by geographical separation. And variation among them may be another reason for species emergence, but the main reason is their change during DNA replication. In self-pollinated species, there is very little chance of new changes or variations occurring in new generations.

Q3. Will geographical isolation be a major factor in the speciation of an
organism that reproduces asexually? Why or why not? 

Ans: Organisms produced in asexual reproduction are almost identical to each other and there is very little difference between them. Variations in this process occur only during DNA replication and these variations are very rare. Geographical separation can be a major factor in the emergence of species because due to this, the organisms that survive in the new environment generate new ones inside themselves.

Page no. 156

Q1. Give an example of characteristics being used to determine how close
two species are in evolutionary terms.

Ans: Examples of Evolutionary Relationship Determination of Two Species:- Like birds, reptiles and water-land animals, mammals also have four legs. Even if their infrastructure has been transformed to perform different tasks on one. In this way, we can understand these relations only by homologous features.

Q2. Can the wing of a butterfly and the wing of a bat be considered
homologous organs? Why or why not?

Ans: No, they are called homologous parts not social. The structure of the wings of a butterfly and a bat is different. They are not the same in origin and die.

Butterfly wings do not have ears while bats have them.

Q3. What are fossils? What do they tell us about the process of evolution?

Ans: Remains of dead animals, marks on rocks or molds and body impressions of those who were alive thousands of years ago. Such preserved remains are called fossils. These fossils tell us many things about the process of bio-evolution such as which fossils are new and which are old, which species have become extinct. These fossil evolutions can also determine the characteristics of various forms and classes that sometimes describe them.

Page no. 158 

Q1. Why are human beings who look so different from each other in terms
of size, colour and looks said to belong to the same species?

Ans: All humans are members of the same species. For example, DNA with excavation, scheduling and fossil studies. Determination of sequence gives knowledge of different stages of human being. Human ancestors originated from Africa. The ancestors from Africa spread to different regions and some remained there. Thus virtual species have no biological basis.

Q2. In evolutionary terms, can we say which among bacteria, spiders, fish
and chimpanzees have a ‘better’ body design? Why or why not?

Ans: The ancestors of both humans and chimpanzees were the same. Chimpanzee can perform its activities like humans. But due to the excessive complexity, there are also flaws in the physical design from the point of view of development, but still bacteria are better than spiders and fish.Answer: The ancestors of both humans and chimpanzees were the same. Chimpanzee can perform its activities like humans. But due to the excessive complexity, there are also flaws in the physical design from the point of view of development, but still bacteria are better than spiders and fish.

8. Heredity

TextBook Exercise

Class 10 Science English Updated : 30 July 2026

TextBook Exercise

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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. This suggests that the genetic make-up of the tall parent can be depicted as

(a) TTWW     

(b) TTww     

(c) TtWW     

(d) TtWw

Ans: (c) TtWW   

Q2. An example of homologous organs is

(a) our arm and a dog’s fore-leg.

(b) our teeth and an elephant’s tusks.

(c) potato and runners of grass.

(d) all of the above.

Ans: (d) all of the above.

Q3. In evolutionary terms, we have more in common with

(a) a Chinese school-boy.

(b) a chimpanzee.

(c) a spider.

(d) a bacterium.

Ans: (a) a Chinese school-boy. 

Q4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Ans: On this basis it can be eaten. that the symptom of light colored eyes is dominant. Since the parents also have light colored eyes, we would call the dominant trait light coloured, although the dark colored trait is recessive.

Q5. How are the areas of study – evolution and classification – interlinked?

Ans: The ancestors of humans were the same. Gradually the organisms evolved and due to this development, the organisms easily progressed towards complexity and were classified into different categories. Thus, biological evolution is the ladder of classification

Q6. Explain the terms analogous and homologous organs with examples.

Ans: Those organs which are similar in basic structure but perform different functions, are called homologous organs, for example - birds, water - land, others have four legs but everyone's functions are different. On the contrary, those organs whose basic structure is not the same but perform the same functions in different organisms are called homologous organs. Example - Wings of bats and birds. The wings of a bat are formed by the expansion of the skin between the extended fingers, but the spread of the skin of the entire forearm of the bird.

Q7. Outline a project which aims to find the dominant coat colour in dogs.

Ans: For this purpose we have to take one black dog and one white colored dog. If after crossbreeding between the two, all the children are born of black color, then we can say that black color is dominant and white color is recessive.

Q8. Explain the importance of fossils in deciding evolutionary relationships.

Ans: Fossils are the remains of those organisms which are now extinct. When we compare the structure of the fossils of those organisms with the present organisms, then we get to know how the organisms evolved and also explain the evolutionary order system.

Q9. What evidence do we have for the origin of life from inanimate matter?

Ans: In 1929, British scientist J.B.S. Haldane suggested that perhaps some complex organic molecules were synthesized which were essential for living things. Elementary organisms may have arisen by other chemical synthesis. It had molecules of ammonia, methane, and hydrogen sulfide but no oxygen. After a week, 15 percent of the carbon was converted into simple organic compounds when sparks were created in a mixture of gases at temperatures below 1000 C. They also synthesized the amino acids that make up protein molecules. In this way living beings arose from inorganic substances.

Q10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Ans: Asexual reproduction variations are very less because DNA replication is almost the same, so there is a lot of similarity in the offspring. In this process, the variations of DNA are permanent and are also beneficial for the survival of the species.

Q11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Ans: In sexual reproduction, the gin set is not in the form of only one DNA chain. Two independent molecules of DNA consist of two chromosomes. In sexual reproduction, the offspring receives two chromosomes - one from the pupa and one from the mother. The symptom which is effective is visible in the child.

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? 

Ans: Yes, it is true. Nature selects the particles of the living beings. Those organisms which show diversity and adapt themselves to the environment are able to survive. On the contrary, those that do not show variation, get extinct. Example - A decrease in the number of tigers due to the unfavorable environment.

8. Heredity

Additional Questions With Solutions

Class 10 Science English Updated : 30 July 2026

Extra Important Questions with Answers – Chapter 8: Heredity

Q1: What is heredity?

Ans: Heredity is the process by which characteristics are passed from parents to their offspring through genes.

Q2: What are inherited traits?

Ans: Inherited traits are characteristics that are passed from parents to offspring through genes.

Q3: What are acquired traits?

Ans: Acquired traits are characteristics developed during an individual's lifetime due to environmental influences. They are not inherited.

Q4: What is variation?

Ans: Variation refers to the differences in characteristics among individuals of the same species.

Q5: Why is variation important?

Ans: Variation helps organisms adapt to changing environmental conditions and increases their chances of survival.

Q6: What is a gene?

Ans: A gene is the basic unit of heredity that controls the inheritance of a specific trait.

Q7: Where are genes located?

Ans: Genes are located on chromosomes inside the nucleus of a cell.

Q8: What are chromosomes?

Ans: Chromosomes are thread-like structures made of DNA and proteins that carry genetic information.

Q9: What is DNA?

Ans: DNA (Deoxyribonucleic Acid) is the genetic material that carries hereditary information from one generation to the next.

Q10: What is a trait?

Ans: A trait is a specific characteristic or feature of an organism, such as eye color or plant height.

Q11: What is Mendel's law of dominance?

Ans: Mendel's law of dominance states that when two contrasting traits are present together, only the dominant trait is expressed in the offspring.

Q12: What are dominant and recessive traits?

Ans: A dominant trait is expressed even in the presence of one dominant allele, while a recessive trait is expressed only when both alleles are recessive.

Q13: What is an allele?

Ans: An allele is an alternative form of the same gene that controls a particular trait.

Q14: What is genotype?

Ans: Genotype is the genetic makeup or combination of alleles present in an organism.

Q15: What is phenotype?

Ans: Phenotype is the observable physical appearance or expressed characteristics of an organism.

Q16: Differentiate between genotype and phenotype.

Ans: Genotype refers to the genetic constitution of an organism, whereas phenotype refers to its visible characteristics.

Q17: What is a monohybrid cross?

Ans: A monohybrid cross is a cross involving only one pair of contrasting traits.

Q18: What phenotypic ratio is obtained in the F₂ generation of a monohybrid cross?

Ans: The phenotypic ratio is 3 : 1.

Q19: What genotypic ratio is obtained in the F₂ generation of a monohybrid cross?

Ans: The genotypic ratio is 1 : 2 : 1.

Q20: What is a dihybrid cross?

Ans: A dihybrid cross is a cross involving two pairs of contrasting traits.

Q21: State Mendel's law of segregation.

Ans: The two alleles of a gene separate during gamete formation, and each gamete receives only one allele.

Q22: State Mendel's law of independent assortment.

Ans: Different pairs of alleles assort independently during gamete formation.

Q23: What is a sex chromosome?

Ans: Sex chromosomes determine the sex of an individual. In humans, they are X and Y chromosomes.

Q24: How is the sex of a child determined in humans?

Ans: The father determines the sex of the child. An X-bearing sperm produces a girl (XX), while a Y-bearing sperm produces a boy (XY).

Q25: Why can't acquired traits be inherited?

Ans: Acquired traits do not affect the DNA of reproductive cells, so they cannot be passed on to the next generation.

Q26: Why are variations beneficial to a species?

Ans: Variations help species survive environmental changes and increase the chances of evolution.

Q27: What is evolution?

Ans: Evolution is the gradual change in inherited characteristics of organisms over many generations.

Q28: What is the relationship between heredity and evolution?

Ans: Heredity passes variations to offspring, and the accumulation of useful variations over generations leads to evolution.

Q29: Why did Mendel choose pea plants for his experiments?

Ans: Mendel chose pea plants because they have distinct contrasting traits, a short life cycle, and can self-pollinate as well as cross-pollinate easily.

Q30: Name any four contrasting characters studied by Mendel in pea plants.

Ans: Tall/Dwarf plants, Round/Wrinkled seeds, Yellow/Green seeds, and Violet/White flowers.

8. Heredity

Long Additional Questions With Solutions

Class 10 Science English Updated : 30 July 2026

Long Additional Questions with Solutions – Chapter 8: Heredity

Q1: What is heredity? Explain the importance of heredity and variation in living organisms.

Ans: Heredity is the process by which characteristics are passed from parents to their offspring through genes. Genes are present on chromosomes and carry hereditary information from one generation to the next.

Variation refers to the differences in characteristics among individuals of the same species.

Importance of Heredity and Variation:

• Heredity helps maintain the continuity of species.
• Variation enables organisms to adapt to changing environmental conditions.
• Useful variations improve the chances of survival.
• Variation forms the basis of evolution.
• It helps species survive natural disasters and diseases.

Q2: Explain Mendel's monohybrid cross with the help of an example.

Ans: A monohybrid cross is a cross between two parents differing in one pair of contrasting characters.

Mendel crossed a pure tall pea plant (TT) with a pure dwarf pea plant (tt).

F₁ Generation:

• TT × tt
• All offspring were Tt (Tall).

F₂ Generation:

• Tt × Tt
• Phenotypic Ratio = 3 Tall : 1 Dwarf
• Genotypic Ratio = 1 TT : 2 Tt : 1 tt

This experiment led Mendel to propose the Law of Dominance and the Law of Segregation.

Q3: State and explain Mendel's three laws of inheritance.

Ans:

1. Law of Dominance

When two contrasting traits are present together, only the dominant trait is expressed in the offspring.

2. Law of Segregation

The two alleles of a gene separate during gamete formation, and each gamete receives only one allele.

3. Law of Independent Assortment

Different pairs of alleles are inherited independently of one another during gamete formation.

These laws explain how traits are inherited from one generation to another.

Q4: Differentiate between inherited traits and acquired traits with suitable examples.

Ans:

Inherited Traits	Acquired Traits
Passed from parents through genes.	Developed during an individual's lifetime.
Can be inherited.	Cannot be inherited.
Controlled by DNA.	Caused by environment or habits.
Example: Blood group, eye color.	Example: Muscular body, scars.

Q5: Explain the mechanism of sex determination in human beings.

Ans:

Human beings have 46 chromosomes, including one pair of sex chromosomes.

• Female: XX
• Male: XY

The mother always contributes an X chromosome through the egg.

The father produces two types of sperms:

• X-bearing sperm
• Y-bearing sperm

If an X-bearing sperm fertilizes the egg, the child will be XX (Girl).

If a Y-bearing sperm fertilizes the egg, the child will be XY (Boy).

Therefore, the father is responsible for determining the sex of the child.

Q6: Explain the relationship between heredity and evolution.

Ans:

Heredity transfers genetic information from parents to offspring. During reproduction, small variations arise due to genetic recombination and mutations.

Some variations help organisms survive better in changing environments. These useful variations are inherited by future generations.

Over many generations, the accumulation of such favorable variations results in evolution.

Thus, heredity provides continuity, while variation drives evolution.

Q7: Why did Gregor Mendel choose pea plants for his experiments? Explain.

Ans:

Mendel selected pea plants because they possessed several useful characteristics.

• They had many clearly distinguishable contrasting traits.
• They had a short life cycle.
• They produced a large number of offspring.
• They naturally self-pollinated but could also be cross-pollinated easily.
• Pure breeding varieties were easily available.

These features made pea plants ideal for studying inheritance.

Q8: Explain the significance of variation in the process of evolution.

Ans:

Variation is essential for the survival and evolution of species.

• It helps organisms adapt to changing environmental conditions.
• Useful variations increase survival and reproductive success.
• Natural selection favors beneficial variations.
• Over generations, these variations accumulate and lead to the formation of new species.
• Without variation, evolution would not occur.

Q9: Describe the structure and function of genes, chromosomes, and DNA.

Ans:

• DNA (Deoxyribonucleic Acid): The hereditary material that stores genetic information.
• Gene: A small segment of DNA that controls a specific inherited trait.
• Chromosome: A thread-like structure made of DNA and proteins that carries thousands of genes.

Genes present on chromosomes carry hereditary information from parents to offspring.

Q10: Explain how Mendel's experiments laid the foundation of modern genetics.

Ans:

Gregor Mendel is known as the Father of Genetics because his experiments on pea plants explained the basic principles of inheritance.

• He proved that traits are controlled by factors (now called genes).
• He introduced the concepts of dominant and recessive traits.
• He explained how traits are transmitted from one generation to the next.
• He proposed the Laws of Dominance, Segregation, and Independent Assortment.
• His discoveries became the foundation of modern genetics and heredity.

Large question with answer

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Q1. 'Different species use different strategies to determine sex of a newborn individual. It can be environmental cues or genetically determined'. Explain the statement by giving example for each. 

Answer: Different species use very different strategies for this. Some rely entirely on environmental cues. Thus, in some animals, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female. In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined. However, in human beings, the sex of the individual is largely genetically determined. In other words, the genes inherited from our parents decide whether we will be boys or girls.

Q2. 

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