LAQ for Heredity and Evolution Class 10 Science NCERT
Important Questions1
(a) Why did Mendel choose garden pea for his experiments? Write two reasons.
(b) List two contrasting visible characters of garden pea Mendel used for his experiment.
(c) Explain in brief how Mendel interpreted his results to show that the traits may be dominant or recessive.
Answer
(a) Reasons:
(i) Pea plant is small and easy to grow.
(ii) A large number of true breeding varieties of that dwarfness is recessive character. Pea plant are available.
(iii) Short life cycle.
(iv) Both self and cross-pollination can be made possible.
(b) Contrasting characters:
(i) Round /Wrinkled seeds
(ii) Tall/Short plants
(iii) White/Purple flowers
(iv) Green/Yellow seeds (or any other)
(c) When Mendel crossed two pea plants with a pair of contrasting characters, only one character appeared in all the members of F1 progeny and the others remain hidden.
On selfing F1, the hidden characters reappeared in just 25% of the offsprings and the other 75% shared the characters expressed in F1.
Mendel concluded that the character which expresses itself in F1 and in 75% of the individuals of F2 is dominating while the other is recessive. (Or same thing can be explained by using an example)
2
How do Mendel's experiments show that
(a) traits may be dominant or recessive ?
(b) inheritance of two traits is independent of each other ?
Answer
(a) Mendel conducted a Monohybrid cross/(crossed pure tall pea plants with pure dwarf pea plants) he observed only tall pea plants in the F1 generation, but on self-crossed the F1 progeny, both tall and dwarf pea plants were observed in F2 generation in the ratio 3 : 1. Appearance of tall character in F1 and F2 generation shows tallness to be a dominant character. But absence of dwarf character in F1 and its reappearance in F2 confirms that dwarfness in recessive character.
(b) Mendel conducted a dihybrid cross and observed that though he started with two types of parents, he obtained four types of individuals in F2. The appearance of new recombination in F2 generations along with parental type characters showed that traits are inherited independently of each other.
3
Answer
(a) Mendel explained this through his monohybrid cross.
He produced progeny from purely dwarf & purely tall plants of pea and he found that all F1 progeny were tall.
But when he used F1 progeny to produce F2 progeny, then 25% of plants (pea plant) were short and ¾ were tall. From this he concluded that bath tallness & dwarfness were inherited in F1 progeny but dwarfness was suppressed under the dominance of other.
Thus he concluded that it is possible that a trait is inherited but not expressed in an organism.
4
Answer
Acquired traits: Traits which develop in the life time of an individual and do not pass to the progeny.
Example : Learnings a skill such as dance/music/loss of body parts/weight/ any other example.
Inherited traits : Traits present in the gamete/germ cells which can be seen in the progeny.
Example : Skin/colour/eyebrow/any other example.
Reason : Traits/characteristics acquired during one’s life time do not bring any change in the DNA of the reproducing cells/germ cells.
Example : Decrease in body weight of beetles due to starvation do not pass on to the next generation because there is no change in the germ cells of beetles.
Detailed Answer :
Acquired traits are the characters that are acquired by the individual during its lifetime. These traits cannot be inherited. For example, if a wrestler develops large muscles due to his program that does not mean it will be passed on to his offspring.
Inherited traits are the characters which are inherited by the offspring from the parents. These are expressed in the offspring and later carried on to the next generation. For example skin colour, eye colour and shape.
Acquired traits occur due to changes in the lifestyles, injury, loss of body parts and disuse of some parts. These traits/experiences occur in the somatic cells which do not involve germ cells and genetic materials. Therefore, these traits are not transmitted or inherited in the next generation. Example, low weight of a starving beetle.
5
(i) What is meant by traits of an individual?
(ii) Explain inherited trait and acquired trait.
(iii) Define specification. List the factors which could lead to rise of a new species.
Answer
(i) Traits: A characteristics feature is called trait.
(ii) Inherited traits are the traits which an organism acquires in life time.
(iii) Formation of new species from the existing ones is called specification.
Factors which could lead to the rise of new species are: geographical isolation, genetic drift , natural selection.
6
(i) Explain whether traits like eye colour or height is genetically inherited. Do power to lift weights and reading French also belong to the same category?
(ii)How do variations affect the evolution of those organisms that reproduce sexually?
Answer
(i) Yes, eye colour and height are genetically inherited traits, as these are expressed by genes. No, weight lifting and reading French do not belong to the same category. They are acquired traits.
(ii) Variations in individual during sexual reproduction give survival advantages to them, and help them to adapt even in extreme environments.
7
Answer
Evolution the process of change from simple life forms to complex life forms by gradual change. It is generating diversity and shaping the diversity.
• It occurs over the course of time and generations by variation, speciation, natural selection, Genetic drift etc., Fossils are the preserved traces of living organisms.
• It helps us to find the intermediate forms in between two classes etc., For example fossil of Archaeopteryx helps us to know better about the intermediate from between reptiles and Aves.
• It is tells us about the extinct species through the fossil or their retained body impressions.
• It helps to know the evolutionary relationships.
• This also shows the line of development from primitive to complex organisms e.g. Ammonite, trilobite, Rajasaurus etc., according to the depth of the layer in which it is found.
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Answer
(i) Speciation: The process of formation of a new species from a pre-existing one.
(ii) Four factors that lead to speciation are:
• Genetic drift
• Mutation/Drastic change in the genes or DNA
• Natural selection
• Geographical isolation
(iii) Geographical isolation cannot be a major factor in the speciation of a self-pollinating plant species.
(iv) Reason : Physical barrier cannot be created in self-pollinating plants.
9
Answer
(a) It is a evolutionary process by which new species arise.
Factors :
• Geographical isolation
• Genetic drift
• Natural selection
• Mutation
(b) (i) Genetic Drift : It is the random change in the frequency of alleles in a population over successive generations due to sampling error in the gametes. Each new generation differs from its parental generation with regard to the allele frequencies simply because of random variation in the distribution of gametes.
This process is more rapid in smaller population, hence, genetic drift can cause less of genetic diversity if there are no counteracting factors.
(ii) Natural Selection: It is the process, according to Darwin, which brings about the evolution of new species of animals and plants. Darwin found that variations existed between individuals of the population and concluded that disease, competition and other forces acting on the population eliminated those individuals which are less well adapted to their environment. The surviving population would pass the hereditary advantageous characteristic to their offspring.
10
Name the phenomenon that governs the following:
(i) Green beetles living in green bushes are not eaten by the crows.
(ii) Number of blue beetles in green bushes increases only because the red beetles, living there, were trampled by a herd of elephants.
(iii) No ’medium height plants’ are obtained in F1 generation, upon crossing pure tall and dwarf pea plants.
(iv) Trails of mice were surgically removed for several generations, still mice had tails in the following generations.
(v) A migrant beetle reproduces with the local population; as a result of migrant beetle enter the new population.
Answer
(i) Natural selection
(ii) Genetic drift
(iii) Law of Dominance
(iv) Acquired characters are not inherited
(v) Gene flow.
11
Answer
(i) Fossils: the remains/impression of dead/decayed plants/ animals of the part.
(ii) Formation of fossils: Formed when dead organisms are compressed under high pressure deep under the soil.
(iii) Two methods of determining the age of fossils are:
(a) Relative method,
(b) Carbon dating method.
(iv) Importance of fossils: (a) The presence of fossilized remains of the organisms is the evidence of existence of the organisms millions of years ago, out of which some have become extinct.
(b) Fossils also helps in the determination of the connecting links between various groups and their origin from the primitive ones.
12
(a) What are fossils and how is age of fossils determined ?
(b) During artificial selection, which features of wild cabbage were selected to give rise to
(i) Cabbage and,
(ii) Cauliflower.
Answer
(a) Body or its parts that are not decomposed/preserved traces of organisms.
• Upon digging the earth, the fossils that are found closer to the surface are more recent than the fossils in deeper layers.
• By detecting the ratios of different isotopes of the same element in the fissil material.
(b) (i) By selecting very short distances between leaves.
(ii) By selecting sterile flowers.
13
Explain with an example for each, how the following provides evidences in favour of evolution in organisms:
(i) Homologous organs
(ii) Analogous organs
(iii) Fossils.
Answer
(i) Homologous organs: Forelimb of human and bird are homologous organs. They have same structural design and developmental origin, but they have different functions and appearance. Homologous organs help us to understand that the organism have evolved from a common ancestor. The more common characteristics the two species have, the more closely they are related.
(ii) Analogous organs: Analogous organs are those organs which have different basic structural design and development origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. They have a common function of flying, but their origins are not common. So, birds and bats are not closely related.
(iii) Fossils and their study is useful in knowing about the species which are no longer alive.
They provide evidence and missing links between two classes. They are helpful in forming a sequence of organisms in the pathway of evolution.
Thus, fossils have an importance in deciding evolutionary relationship. Archaeopteryx is a fossil bird. It had feathers, fuses bones and beak which are exclusively bird structures. It also had some features which are found in reptile e.g., teeth in jaw, claws on free fingers and a long tail. This fossil provides a clue that birds have evolved from reptiles.
14
Answer
Fossils are remains or impressions of past organisms that are found in the rocks. Fossils of lower strata belong to early periods while those of upper strata are of later periods. Arranging the fossils stratum wise will indicate the occurrence of different forms of life at different times. It is found that the early fossils generally belong to simple organisms. Complexity and elaboration increased gradually with evolution.
Importance of fossils :
(i) Fossils indicate the path of evolution of different groups.
(ii) They can indicate the phylogeny of some organisms. E.g., horse, elephants.
(iii) Some fossils have characteristics intermediate between two groups.
They indicate how one group has evolved from another.