Intext Questions

Q.1       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?
Sol.

Trait B is likely to have arisen earlier because it is present in a larger portion of the population.

---

Q.2       How does the creation of variations in a species promote survival?
Sol.

Variations take place in response to the changes in the environment. Such variations enable a species to cope with the new changes. Thus, variations help a species in survival.

---

Q.3       How do Mendel’s experiments show that the traits may be dominant or recessive?
Sol.

During monohybrid cross by Mendel, one of the pair of traits did not appear in the F1 generation. But that trait appeared in the F2 generation. Based on this observation, Mendel concluded that a trait could be dominant or recessive.

---

Q.4       How do Mendel’s experiments show that traits are inherited independently?
Sol.

During dihybrid cross by Mendel, it was observed that when two pairs of traits were considered; each trait expressed independent of the other. Thus, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits.

---

Q.5       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 trait – blood group A or O – is dominant? Why or why not?
Sol.

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

---

Question – 6 – How is the sex of a child determined in human beings?
Sol.

Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23rd pair is composed of different types of chromosomes which are named as X and Y chromosomes. The 23rd pair contains one X and one Y chromosome in a male. On the other hand, the 23rd pair in a female contains X chromosomes. This means that all the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome as the 23rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote would develop into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child.

---

Q.7       What are the different ways in which individuals with a particular trait may increase in a population?
Sol.

When a beneficial trait appears, it can increase in a population. The example of blue beetles in the chapter shows this. Since blue beetles could not be spotted by the crows hence more blue beetles could survive. Sometimes, an accident can also lead to proliferation of a new trait in a population, as happened in the example of trampling of bushes by elephants. It can be said that sudden or gradual changes in the environment or some mutation in a species can lead to a particular trait being passed on through generations.

---

Q.8       Why are traits acquired during the lifetime of an individual not inherited?
Sol.

Acquired traits do not bring any change in the genotype of an individual. Hence, acquired traits do not get inherited.

---

Q.9       Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Sol.

Small numbers of surviving tigers means that a small gene pool of tigers is left. A smaller population reduces the chances of variations. A time may come when lack of useful variations may result in extinction of tigers. Hence, a small number of surviving tigers is a cause of worry from the point of view of genetics.

---

Q.10      What factors could lead to the rise of a new species?
Sol.

Speciation can happen if two groups of the same species are somehow prevented from interbreeding for several generations. This can happen because of geographical segregation or because of some genetic changes.

---

Q.11      Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Sol.

In a self-pollinating plant species, geographical segregation cannot be a major factor in speciation, because no new trait can become a part of the genotype in self-pollination plant species. However, there are some chances of some environmental changes which can lead to some variations.

---

Q.12       Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not ?
Sol.

In case of an asexually reproducing organism, geographical isolation cannot be a major factory in speciation because meiosis does not take place during asexual reproduction.

---

Q.13       Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Sol.

Let us take the example of humans and apes. Both of them have similar body design. Body hair and mammary glands are present in both the animals. Hence, these two animals are closely related in evolutionary term. Now take some common characters between a fish and a man. Vertebral column, brain box and jaws are present in both of them. But fish and man look entirely different from each other. Hence, they are not very closely related in evolutionary term; rather are like distant relatives.

---

Q.14       Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Sol.

Wings of a butterfly are composed of chitinous membrane, while wings of a bat are composed of bony skeleton. Hence, these are not homologous organs rather analogous organs.

---

Q.15       What are fossils? What do they tell us about the process of evolution?
Sol.

The preserved remains of animals or plants or other organisms from the distant past are called fossils. These fossils tell us about many extinct animals and also give insights into how the evolution could have taken place.

---

Q.16       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?
Sol.

In spite of wide differences in size, colour and looks, human beings can interbreed. Hence, all of them are kept under one species.

---

Q.17       In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Sol.

It depends on our perception of ‘better’ design. If complexity of body design is the criterion, then chimpanzee is obviously better than bacteria. But if ability of survival in almost all kinds of habitat is a criterion then bacteria are far ahead than any other group of organisms.

Exercise

Q.1       A Mendelian experiment consisted of breeding tall pea plant 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 makeup of the tall parent can be depicted as?
             (a) TTWW                                   (b) TTww  
             (c) TtWW                                     (d) TtWw
Sol.       (c) TtWW

---

Q.2       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 a grass
             (d) All of the above
Sol.       (d) All of the above

---

Q.3       In evolutionary terms, we have more in common with
             (a) A Chinese boy
             (b) A chimpanzee
             (c) A spider
             (d) A bacterium
Sol.       (a) A Chinese boy

---

Q.4       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?
Sol.

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

---

Q.5       How are the areas of study; evolution and classification interlinked?
Sol.

The modern system of classification is also called phylogenetic classification; which means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

---

Q.6       Explain the term analogous and homologous organs with examples.
Sol.

Homologous Organs: Organs which have common design but serve different functions in different animals are called homologous organs. For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals. Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools. This shows that frogs, birds and humans have evolved from a common ancestor.

Analogous Organs: Organs which have different design but serve a common function in different animals are called analogous organs. Wings of birds and wings of bat are good examples of a pair of analogous organs. Wings of birds are composed of all the bones of forelimb and are covered with feathers. Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure. Yet wings in both the organisms are used for flying.

---

Q.7       Outline a project which aims to find the dominant coat colour in dogs.
Sol.

For this, take a male dog with brown coat and bitch with white coat. Cross them to get the F1 generation. After that, allow the F2 generation to come into being. Tabulate data from two generations and find out the dominant coat colour.

---

Q.8       Explain the importance of fossils in deciding evolutionary relationships.
Sol.

There are certain animals which became extinct millions of years ago. Fossils of many of such animals give important clues about missing links in the evolutionary relationship. The fossil of archaeopteryx is a good example of missing link. The fossil of archaeopteryx shows characters of birds and reptiles; which suggests that birds have evolved from reptiles. This example shows the importance of fossils in deciding evolutionary relationships.

---

Q.9       What evidence do we have for the origin of life from inanimate matter?
Sol.

The famous experiment by Miller and Urey could establish that life originated from inanimate matter. These scientists replicated the conditions which may have existed during the early years of origin of the earth. In that experiment, inorganic substances gave rise to amino acids. Amino acid; we know are the bases of various biomolecules.

---

Q.10      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?
Sol.

During sexual reproduction, genotype of the progeny is contributed by two different individuals. This opens up scope for various permutations and combinations. Moreover, the crossing over during meiosis is another means for producing variations. Hence, there are more chances of variations during sexual reproduction than during asexual reproduction.

---

Q.11      How is the equal genetic contribution of male and female parents ensured in the progeny?
Sol.

Gametogenesis involves meiosis which leads to haploidy in the gametes. A zygote thus gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from male and female parents.

---

Q.12      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?
Sol.

This statement is true to some extent. There are many apparent variations which help an individual in survival. But there are certain variations which may not be beneficial, yet they are inherited through subsequent generations. The colourful plumage of peacock is a good example. The colourful plumage of a peacock helps it in finding a suitable mate but it also makes it conspicuous for its predators.

Exemplar

Multiple Choice Questions :

Q.1  Exchange of genetic material takes place in
(a) Vegetative reproduction
(b) Asexual reproduction
(c) Sexual reproduction
(d) Budding
Sol. (c)

---

Q.2 Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(a) Double fertilisation
(b) Self pollination
(c) Cross fertilisation
(d) No fertilisation
Sol.(b)

---

Q.3 A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because
(a) Tallness is the dominant trait
(b) Shortness is the dominant trait
(c) Tallness is the recessive trait
(d) Height of pea plant is not governed by gene ‘T’ or ‘t’
Sol. (a)

---

Q.4 Which of the following statement is incorrect?
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene
Sol. (d)

---

Q.5 If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F1 generation are
(a) Round and yellow
(b) Round and green
(c) Wrinkled and green
(d) Wrinkled and yellow
Sol. (a)

---

Q.6 In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome is/are
(i) Large chromosome
(ii) Small chromosome
(iii) Y-chromosome
(iv) X-chromosome
(a) (i) and (ii)
(b) (iii) only
(c) (iii) and (iv)
(d) (ii) and (iv)
Sol. (c)

---

Q.7 The maleness of a child is determined by
(a) The X chromosome in the zygote
(b) The Y chromosome in zygote
(c) The cytoplasm of germ cell which determines the sex
(d) Sex is determined by chance
Sol. (b)

---

Q.8 A zygote which has an X-chromosome inherited from the father will develop into a
(a) boy
(b) Girl
(c) X- chromosome does not determine the sex of a child
(d) Either boy or girl
Sol. (b)

---

Q.9 Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in evolution

(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution
Sol. (b)

---

Q.10 New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) Chromosome number changes in the gamete
(iii) There is no change in the genetic material
(iv) Mating does not take place
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)
Sol. (a)

---

Q.11 Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F₁ progeny that have round, yellow (RrYy) seeds. When F₁ plants are selfed, the F₂ progeny will have new combination of characters. Choose the new combination from the following
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
(a) (i) and (ii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)
Sol. (b)

---

Q.12 A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato
Sol. (c)

---

Q.13 Select the correct statement
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous
Sol. (a)

---

Q.14 If the fossil of an organism is found in the deeper layers of earth, then we can predict that
(a) The extinction of organism has occurred recently
(b) The extinction of organism has occurred thousands of years ago
(c) The fossil position in the layers of earth is not related to its time of extinction
(d) Time of extinction cannot be determined
Sol. (b)

---

Q.15 Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction
Sol. (a)

---

Q.16 A trait in an organism is influenced by
(a) Paternal DNA only
(b) Maternal DNA only
(c) Both maternal and paternal DNA
(d) Neither by paternal nor by maternal DNA
Sol. (c)

---

Q.17 Select the group which shares maximum number of common characters
(a) Two individuals of a species
(b) Two species of a genus
(c) Two genera of a family
(d) Two genera of two families
Sol. (a)

---

Q.18 According to the evolutionary theory, formation of a new species is generally due to
(a) Sudden creation by nature
(b) Accumulation of variations over several generations
(c) Clones formed during asexual reproduction
(d) Movement of individuals from one habitat to another
Sol. (b)

---

Q.19 From the list given below, select the character which can be acquired but not inherited
(a) Colour of eye
(b) Colour of skin
(c) Size of body
(d) Nature of hair
Sol. (c)

---

Q.20 The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) Copies of the same chromosome
(b) Two different chromosomes
(c) Sex chromosomes
(d) Any chromosome
Sol. (a)

---

Q.21 Select the statements that describe characteristics of genes
(i) Genes are specific sequence of bases in a DNA molecule
(ii) A gene does not code for proteins
(iii) In individuals of a given species, a specific gene is located on a particular chromosome
(iv) Each chromosome has only one gene
(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Sol. (b)

---

Q.22 In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
(a) 1 : 3
(b) 3 : 1
(c) 1 : 1
(d) 2 : 1
Sol. (c)

---

Q.23  The number of pair (s) of sex chromosomes in the zygote of humans is
(a) One
(b) Two
(c) three
(d) four
Sol. (a)

---

Q.24 The theory of evolution of species by natural selection was given by
(a) Mendel
(b) Darwin
(c) Morgan
(d) Lamarck
Sol. (b)

---

Q.25 Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
(a) Reptiles have evolved from birds
(b) There is no evolutionary connection between reptiles and birds
(c) Feathers are homologous structures in both the organisms
(d) Birds have evolved from reptiles
Sol. (d)