• CBSE - Grade 10 - NCERT - SCIENCE Chapter - Heredity And Evolution


    Answers to NCERT Questions:



    In evolutionary terms, we have more in common with

    A  A Chinese school-boy

    B  A chimpanzee

    C  A spider

    D  A bacterium


    Answer: A Chinese school-boy

    According to the theory of evolution, organisms of the same species have more in common than organisms of different species. We have more in common with a Chinese school-boy because both belong to the Homo sapiens species. Both have same ancestors.



    Explain the terms analogous and homologous organs with examples.

    Analogous organs : The organs which have similar functions but different anatomical structures are called analogous organs. Examples:

    • Wings of a bird and an insect.

    • Pectoral fins of sharks and flippers of dolphins.

    • Eyes of octopus and mammals.


    Homologous organs : The organs which have different functions but same anatomy are called homologous organs. Examples:

    • Forelimbs of man, whale, bat, cheetah

    • Mouth parts of cockroach, honey bee, butterfly

    • Thorns of Bougainvillea and tendril of Cucurbita



    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?

    The fusion of male and female gametes (sperms and ovum respectively) results in sexual reproduction. Sexual reproduction causes more viable variations because:

    • There could be an error in the copying of DNA, though this is a rare condition

    • Chromosomes of maternal and paternal origin are randomly segregated at the time of gamete formation

    • There is an exchange of genetic material between homologous chromosomes during gametes formation

    In case of asexual reproduction, the chances of variation are significantly less because only one parent is involved in the process of reproduction. Few variations that happen in these organisms is due to the inaccuracies happening when copying DNA onto the progeny is erroneous. Generally, offsprings produced as a result of asexual reproduction are generally genetically similar to their parents.



    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?

    I agree with the statement that only variations that confer an advantage to an individual organism will survive in a population. All variations do not necessarily provide an equal chance of survival to an organism in the environment. Chances of survival depend on the nature of variations. For example - a variation leading to the increase of heat-resistant bacteria is beneficial to the bacteria for its survival.



    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?

    If we know the genotype of the variants of the trait, we cannot tell which trait is dominant or recessive. 

    Unless we have the information on the genotype of a particular trait, we cannot arrive at  any conclusion.




    How are the areas of study of evolution and classification interlinked?


    The study of evolution and classification of organisms are interlinked in a phylogenetic classification system.

    Classification of organisms based on their descent from a common ancestor is called Phylogenetic classification.

    Different types of organisms are classified in different groups based on similarities and dissimilarities between them.

    The evolutionary ancestry is the foundation of the phylogenetic classification system. It is based on life's evolution and depicts the genetic relationships between organisms. 

    Phylogenetic classification helps to produce cladograms which include both the ancestor species and the descendants of this species to depict the genetic relationships between organisms.



    Explain the importance of fossils in deciding evolutionary relationships.

    Fossils are the remains or impressions of prehistoric plants or animals embedded in rocks. Fossils are studied to find information about the plants and animals that lived hundreds of years ago and are now extinct. The study helps us to compare the animals that lived during prehistoric times with its present descendants. They provide the missing links in the pathway of evolution by providing information in a sequence of evolution.



    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?


    Trait B



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



    With the passage of time, the genetic variation in an organism helps them to adapt better to the changes in the environment happening constantly. 

    These variations in a population bring stability of these traits and better adaptability in various species rather than getting extinct. 

    Hence, the creation of variation helps in a species promote survival.



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


    Coat colour in dogs is dictated by a variety of genes. At least 11 genes have been identified that affect the colour of the coat in a dog. A dominant gene expresses in both homozygous as well as heterozygous conditions. A recessive gene is only expressed in homozygous condition.

    Let us consider the case of a dog whose one parent is homozygous black (BB) and another parent is homozygous brown (bb). 

    A Cross between the two parents can produce the offspring with the genetic make-up: 

    1. Bb

    2. bB 

    By looking at the genetic make-up, we can’t determine whether Black is dominant or brown is dominant. If we observe the off-springs produced, we can say which one is a dominant trait. If the F1 generation is of black color, we can say black is dominant. Likewise, if the F1 generation is brown then we can say that brown is the dominant trait.


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Material : CBSE - Class 8 - Biology

Topic : NCERT - Mathematics

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