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POINTS TO REMEMBER
Accumulation of Variations During Reproduction
■ Sexual reproduction helps in maximising the numbers of successful variations.
■ The differences in the body designs are inherited from a generation to next generation and with more differences in next generation along with differences of previous generation. These differences goes on accumulating along with new differences at each generation.
■ Sexual reproduction generates great diversity than asexual reproduction. For example, a sugar- cane field and number of animals including human beings. Small differences among individuals are called variations.
■ Depending upon the nature of variation, different individuals have different kinds of advantages. Greater advantage more chances of survival in changed environment.
■ Selection of variants by environmental factors forms the basis of evolutionary process (= natural selection).
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Table of Contents
HEREDITY AND EVOLUTION CLASS 10
1. Describe briefly four ways in which individuals with a particular trait may increase in population.
Ans. The individuals with a particular trait will increase in number if the trait provides:
1. More Food: The trait helps in obtaining more food that leads to increased growth and reproduction.
2. Useful Variations: The trait helps the individuals to adapt to environment and achieve greater success in struggle for existence.
3. Genetic Drift: It causes genetic fixation of a trait which, therefore, occurs in whole of the progeny.
4. Differential Reproduction: The triat gives extra benefit to the individuals in survival and reproduction.
2. “Variations that confer an advantage to an individual organism only will survive in the population.”Justify.
Ans. Useful variations give advantage to individuals in obtaining more food, adaptation to environmental changes and higher success in the struggle for existence. They give benefit in survival and reproduction. Differential reproduction increase the useful variations in the population. Other individuals with harmful variations will be eliminated. For example, some bacteria have ability to tolerate high temperature. In warm environment non-tolerant bacteria will be killed. Others with tolerance to high temperature will survive and multiply.
3.”Red beetles live in bush with green beetles. Eventually, the number of green beetles increases as compared to red beetles.”
(a) Give reason for this increased number of green beetles.
(b) State two advantages of variations.
Ans. (a) Red beetles are quite conspicuous in green bushes. They are picked up by crows for feeding. Green beetles are not easily distinguishable from green leaves of bushes. Therefore, they are not devoured by crows. Population of green beetles will, therefore, increase while that of red beetles will decrease.
(b) Advantages of Variations. (i) Variations function as preadaptations to help the organisms to survive in adverse conditions. (ii) They help individuals in struggle for existence and natural selection.
4. Explain how do organisms create an exact copy of themselves?
Ans. Organisms create an exact copy of themselves in the form of offspring by passing their genetic traits to them. This is done through propagules in asexsul reproduction and gametes in sexual reproduction.
5. A bacterial cell is different from cells of other organisms. Name the feature which makes it different from others.
Ans. Prokaryotic nature while eukaryotic nature (having organized nucleus) is found in other organisms
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8. If A trait exist in 10% population of an asexually reproducing species and a trait-B exist in 60% of the same population which trait in likely to have arisen earlier?
Ans. Trait A and B have not arisen earlier or late since the traits in asexually reproducing species are not inherited newly. They are already there.
9. How does the creation of variations in a species promote surrival?
Ans. A great diversity is generated in sexually reproducing species. Depending on the nature of varations, different individuals would have different kind of advantages under different conditions
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POINTS TO REMEMBER
■ Heredity is the process by which characters and traits are transmitted/ inherited from the parents to the offspring.
■ Inherited traits are those traits which are controlled by genetic material of the individual and are obtained from the parents in inheritance of e.g. height, eye colour, shape of nose, lips, ears, skin colour etc.
■ Due to varied expression of genetic traits, no two individuals are alike in human population.
■ Both father and mother contribute equally equal amount of DNA through their gamete and hence each trait in the child is influenced by both the paternal and maternal DNA. Thus for trait there will be two version in each child. Now what trait in the child will express?
■ Gregor John Mendel in 1856, conducted breeding experiments on garden pea (Pisum sativum) out of sheer interest. His findings became a milestone in biology. He established the basic principle of heredity concerning mechanism of inheritance of characters
■ Mendel took seven varieties of pea plant showing seven pairs of contrasting characters such as tall/dwarf plants; round/wrinkled seeds; white/voalet flower; yellow/green seed colour; green/yellow seed colour; inflated/constricted pod shape: Axial/terminal flower position.
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■ Mendel crossed pure breeding varieties, first by taking only one contrasting character at a time-Monobybrid cross and then by taking two pairs of contrasting characters-Dihybrid cross. He tried with all the seven pairs of contrasting characters in his breeding experiments and found similar observations for all the characters.
■ From the monohybrid cross, Mendel concluded that the first generation (or F, cross) showed the traits of only one parent. i.e., Round seeds. The trait of other plant, wrinkled seeds did not show upon the progeny of first generation. There is no half way characteristic in the first generation, no medium seed shape plant or mixture of two.
■ The trait which expresses in the F₁ generation is called dominant trait and the other which does not express itself, though present is called Recessive trait.
■ When these hybrid plants of F1, generation were self-pollinated, they produced in F2 generation plants with round seeds and plants with wrinkled seeds. These visible form of a character are called phenotypes.
■ Mendel observed that the progeny of the parental plants. the F1, are all round trait. F₂ progeny of F₁, 1/4 of the plants have wrinkled seeds. It indicates both round and wrinkled traits were inherited in the F1, plants and only the round seeds expressed. Thus two copies of the trait are inherited in each sexually reproducing organism.
■ The two copies of the trait may be identical (RR, rr) or may be different (Rr), depending upon the parents.
■ The above cross shows that both RR and Rr are round seeds while rr is a wrinkled seed. It means only a single copy of R is enough to make seeds round while both copies have to be “rr” for the wrinkled seeds.
■ Traits which can express both in the double and single copy (RR, R) are dominant trait and those that express only in double copy (rr) are called recessive traits.
■ Mendel also observed that the traits do not blend or mix up in F, generation otherwise medium shape seed plants would have been produced. Mendel’s experiment showed that traits are inherited independently.
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■ Mendel in his breeding experiments also studied the inheritance of two pairs of contrasting characters-Dihybrid cross. He crossed plants with round green seeds with wrinkled yellow seeds. He observed that the F₁ plants are all have yellow round seeds. It indicates that round and yellow traits are dominant while wrinkled and green traits are recessive.
■ On selfing F₁ plants, he found that F₂ progeny plants are round green seeds, wrinkled yellow seeds, and some round yellow some wrinkled green seeds the new mixture of the parental types. It indicates that the round/wrinkled traits and green/yellow seed traits are independtly inherited. It is the law of independent assortment.
■ Mendel conducted his breeding experiment in three steps (i) selection of pure breeding parent plants (ii) production of F, plants by cross breeding parent plants (iii) raising the F generation by self-pollination of F, (Hybrid) plants.
■ Cellular DNA contains all the information for making all the proteins present in the cell. A segment of DNA which contains the information for making a single protein is called a gene. Proteins are the structures which control different characteristics of the organism.
■ Hormones control the growth and development in plants. The height of a plant depends upon the amount of the hormone which in turn depends upon the efficiency of the process making it i.e., the enzyme needed for this process.
■ If the enzyme works properly a lot of the hormone will be made, resulting in tall plant. If the gene has some alteration it makes the enzyme less effecient, less the amount of hormone, resulting in a short plant. Thus genes control the characteristics or traits of an organism.
■ Both parents contribute equally to the DNA of progeny, each contributing a copy of same gene. It means a organism has two sets of all the genes, one inherited from each parent. Thus each gamete possess only one set of genes.
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■ Each gene set is present as separate independent pieces, each called as chromosome. Thus each cell have two copies of chromosome one from each parent.
■ Every germ cell carry one chromosome from a pair and it may be maternal or paternal origin.
■ When two germ cells fuse, they restore the normal number of chromosomes in the progeny ensuring the stability of DNA of the species.
■ Sex of the new born baby/individual in different species is determined by different ways. In some animals temperature at which the fertilised eggs are kept determine whether the egg will make male or female individuals e.g., turtles.
■ Snails can change their sex indicating sex is not determined genetically.
■ In human beings and other animals, sex is genetically determined.
■ In human beings, 22 pair of chromosomes each have one paternal and one maternal copy. The chromosomes of 23rd pair are called sex-chromosomes which form a odd or perfect pair.
■ Women have a perfect pair of sex chromosomes called XX bull in men the chromosomes of 23 rd pair are odd, mis-matched called ‘XY’ in which X is normal-sized and Y is small.
■ All the children whether boys or girls inherit one X-chromosome from their mothers. Thus the sex of the children is determined on the sex-chromosome which they inherit from their father.
■ A child who inherits X-chromosome from her father will be a girl and the one who inherits a
Y-chromosome from his father will be a boy.
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10. How did Mendel experiments show that different traits are inherited independently? Explain.
Ans. In a Dihybrid cross between pure breeding round green seed pea plants with wrinkled yellow seed pea plant Mendel observed only round yellow plants in F₁ generation. On selfing the plants 200 of F₁ generation, Mendel noticed four types of plants in F2 generation in the ratio of 9 round yellow 3 rounds green! 3 wrinkled yellow! 1 wrinkled green. The appearance of two new types of plants wrinkled yellow and round green indicates that the factors/genes for the seed shape are inherited independent from the factors controlling seed colour. It supports independent inheritance of factors of two characters, shape and colour of a seeds
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11. “The sex of the children is determined by what they inherit from their father and from mother. Justify.
Ans. Ovum produced by would-be-mother is always of one type (22 + X). Sperms produced would-be-father are of two types, gynosperms (22+X) and androsperms (22 + Y) gynosperm (22 + X) fertilizes the ovum (22 + X), the child born will be boy (44+XY Therefore, only father is responsible for the sex of the children.
12. Give one example of each of the characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters.
Ans. Inherited Trait: Fused and Free ear lobes.
Acquired Trait: Muscular body of a wrestler.
Difference: Acquired trait develops during the life time of an individual which affects somatic parts and dies with the death of the individual. Inherited trait is obtained from the parents, influences genes or germ cells and is passed on to the next generation.
13. In case of round yellow and green wrinkled, which is dominant trait set?
Ans. Round yellow.
14. What is the function of genes in an organism?
Ans. Genes are the carrier of the genetic information for the body functions and passage from one generation to another.
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15. What is gene?
Ans. Gene is a unit of inheritance which consists of a linear segment of chromosome or DNA that takes part in expressing a particular character.
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16. In a monohybrid cross between tall Pea plants (TT) and short Pea plants (tt), a scientist observed only tall Pea plants (Tt) in the F₁ generation. However, on selfing the on generation Pea plants the he obtained from both tall and short plants in F2 generation. On the basis of above observations with other angiosperms also, can the scientist arrive at a law? If yes, explain the law. If not, give justification for your answer.
Ans. Yes, the scientist would arrive at the law of dominance. The law states that when both the alleles of a character are present together in an individual, only one expresses its trait. It is called dominant trait. The other trait which remains suppressed though its allele is present is called recessive. This happens in F₁ generation. However, due segregation and chance coming together of the two alleles, both the dominant and recessive traits appear in F₂ generation.
17. List two differences in tabular form between dominant and recessive traits. What percentage/ Proportion of the plants in F2 generation/progeny were round in Mendel’s cross between round and wrinkled seeded Pea plants?
Ans. Differences: Dominant express both in homozygous and heterozygous and in hybrid while recessive do not express in hybrid and only express in homozygous state. The trait of rounded seed is dominant over wrinkled seed. In F2 generation the rounded seed appears in 75% of the population as the phenotypic ratio is 3: 1.
18. How can you say that in Mendelis monohybrid cross, the F₂ dominants are not all the same?
Ans. F2 dominants are externally similar but are genetically of two types, pure and hybrid. This can be proved by allowing them to self breed. One third of the dominants will breed true and produce offspring with only dominant trait. Two third of the dominants will behave as hybrids (like F, individuals) producing both dominant and recessive individuals in the ratio of 3:1.
19. “A trait may be inherited but may not be expressed.” Justify this statement with the help of a suitable example.
Ans. A cross between parents with pure dominants (say TT) and pure recessive (say tt) traits produces hybrids or F₁ individuals with dominant traits only but on self fertilization the F₂ generation comes to have both individuals with dominant and recessive traits in the ratio of 3:1. Obviously, F₁ individuals have received the recessive trait but the same is unable to express itself in the presence of dominants trait.
20. “It is a matter of chance whether a couple will give birth to a boy or a girl.” Justify the statement and support your answer with a neat illustration.
Ans. Mother Produces only one type of eggs, 22 + X Father produces two types of sperms, gynosperms 23 + X and androsperms 22 + Y. The two are produced in equal proportion. It is a matter of chance that an androsperms (22 + Y) or gynosperm (22 + X) first reaches the (22 + X) and fuses with it to form a male or female offspring.
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21. Why are some Pea plants tall and others short in nature? Explain with reference to role of genes in controlling characteristics.
Ans. Genes control characters through the synthesis of specific proteins. The proteins take part in formation of body structures, enzymes, hormones and other biochemical. In case of height in Pea, the protein takes part in producing hormone for growth in height. If the protein is working efficiently, more hormones would be produced and Pea plant becomes tall. However, if the protein is less efficient, small quantity of hormone would be formed and the Pea plant will remain short.
22. State the importance of chromosomal difference between sperms and eggs of humans.
Ans. Human eggs are of one type with a chromosomal complement of 22 + X Human sperms are of two types with chromosomal complements of 22 + X and 22 + Y Sex of the child will be determined by which sperm type fuses with the egg. Sex of the child will be male if 22 + Y sperm fuses with the egg (22 + Y, 22 + X). It will be female if 22 + X sperm fuses with the ovum (22 + X, 22+X).
23. A child questioned his teacher that why do organisms resemble their parents more as compared to grand parents. In through by which way will teacher explain to the child?
Ans. A child receives two chromosomes of each type, one from each parent (50:50). These chromosomes have been inherited from only one of the two paternal grand parents and one of the two maternal grand parents. Hence, resemblance with grand parents will be lesser than resemblance with immediate parents.
24. How do Mendel experiments show that traits may be dominant or recessive?
Ans. In his breeding experiment Mendel cross pollinated a pure male tall pea plant with pure female dwarf pea plant, and he observed only tall plants in F₁ generation. When F₁ tall plants are self trait of pollinated, both tall and dwarf plants produced in F₂ generation in approximately 3:1 ratio. The trait of dwarfs is present in F₁ generation but it was not expressed and only trait of tallness is expressed. The character which expresses in the presence of its contrasting form is termed dominant trait. The trait which remains unexpressed in the presence of its contrasting form is termed recessive trait. Mendel called tall character as dominant and dwarf character as recessive.
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25. 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. No The information provided is not enough to tell us whether the trait of blood group A or blood group O is dominant. Either can be possible because each individual carries two alleles. Q. 67. Recessive trait will appear only when the two alleles are similar. In this case, there are two possibilities.
Possibility I. Blood group A is dominant and blood group O is recessive: The blood group O in daughter can appear only when both the recessive alleles occur together in mother and 0.6 father has one allele of A and other allele of O blood group.
Possibility II. Blood group O is dominant and blood group A is recessive: In this possibility An father must carry both alleles of blood group A while the mother may be having either both alleles of O blood group or one of A blood group and other of O blood group.
26. How is the sex of the child determined in human being?
Ans. In human beings, sex of the child is determined depending upon which type of male gamete fertilizes the female gamete. If male gamete carrying X chromosome fertilizes the egg, the sex of the child will be female. However, if male gamete caring Y chromosome fertilizes the egg, the sex of the child will be male.
POINTS TO REMEMBER
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■ There is inbuilt tendency to variation during reproduction because of errors in DNA.
■ Due to rare variation, frequency of inherited trait changed over generation, constitute the essence of the idea of evolution.
■ Variations which appear may have survival advantage under changed conditions and are naturally selected. Natural selection is exerted by some factors. Natural selection directs the evolution in a population. It results in adaptation in the population to fit their environment better.
■ In small populations, some accidental factor, change the frequency of some genes, then though they give no survival advantage. This phenomenon is called genetic drift. It provides diversity without any adaptations.
■ The population of the organism may expand or contract in size due to the environment factors such as availability of food, diseases without any genetic change. These variations are acquired variations. These are reversible.
■ Variations which does not affect the specialised reproductive tissue/change the DNA of germ cells are not inherited to the progeny and play no role in evolution. Changes in non reproductive cell tissue/somatic tissue cannot be passed on to the DNA of the germ cell and thus cannot direct evolution.
■ Any change which cannot change the genes of the germ cells cannot be inherited to the progeny and hence no evolutionary significance.
■ Ideas of heredity and genetics are essential for Understanding evolution.
■ Charales Darwin who comes up with the idea of evolution of species by natural selection did not know the mechanism whereby Variations arise in the species. It is ironic Darwin and Mendel did not know each other or their work.
■ JBS Haldane, a British scientist proposed that life must have developed from simple inorganic moleculares which were presents on primitive earth at the time of its formation. He speculated that the conditions of earth at that time favoured the formation of complex organic molecules necessary for origin of life. The first primitive organisms (protobionts) arose from the aggregation of these complex organic molecules accompanied with some changes.
■ Miller and Urey 1953, simulated the conditions existed on the early earth and created amino acids from a mixture of ammonia, methane hydrogen sulphide but no oxygen by passing sparks through the mixture of gases below 80 °C. They converted carbon from methane into simple organic compounds of carbon like amino acids a constituent of proteins.
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27. With the help of two suitable examples, explain why certain experiences and traits earned by people during their lifetime are not passed on to their next generations. When can such traits can be passed on?
Ans. Traits acquired during the life type of an individual influence the non-reproducing organs. There is no influence on the DNA of germ cells which transfer traits to offspring. Non reproduction cells have no such role. Traits acquired die with the death of individuals e.g., A pilot flying an aeroplane, a swimmer, Indian ladies boring pinna. The acquired traits can be Ans. passed on in case they affect the germ cells.
28. Explain the formation of sub-population in neighbourhood by taking the example of beetle. Ans. Beetle have a tendency to remain restricted to a few nearby bushes on which they live, feed and reproduce. In a large population of beetles spread over a mountain range, a number of separate segments of population will occur depending upon the spread of groves of bushes. As there is little gene flow among separated segments of population, they develop and accumulate their own variations and from sub-population. A sub-population can further evolve into reproductively isolated population if natural barrier develops between it and other sub-populations, e.g., a glacier, water body, mountain cut.
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29. With the help of a suitable example, explain natural selection.
Ans. Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree trunks in the forests around Manchester were light greyish green due to the presence of lichens. Most of the peppered Moth found in the area were light coloured with dark spots which could not be spotted easily by predator birds. During 1845 to 1890, air pollution killed the lichen flora. The deposition of soot changed the colour of the tree trunks to blackish one. Peppered moth of the area also exhibited switch over to melanic or blackish form. It provided better survival value against dark background. The light grey from largely disappeared as it could be easily spotted by predator birds and devoured.
30. Why are traits acquired during the life time of an individual not inherited?
Ans. It is so because acquired characters involve changes in the non-reproductive tissues only and do not bring any change in the DNA. Any alternation in the DNA of germ cells in fact, is passed
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31. Why are small numbers of surviving tigers a cause of worry from the point of view of gentles?
Ans. Tigers due to over hunting are surviving in limited numbers. if some natural calamity kills all these small population of tigers, they will suddenly becomes extinct as per genetic drift phenomenon.
32. What evidence do we have for the origin of life from inamate matter?
Ans. Miller and Urey experiment. Miller and Urey 1953 simulated an atmosphere thought to exist on early earth. They sparked a mixture of ammonia, methane, hydrogen sulfide but no oxygen, at temperature below 100°C and produced amino acids the component of protein molecules.
33. Give reasons why acquired characters are not inherited.
Ans. Acquired characters are due to changes in somatic cells and not in the DNA of germ cells. Thus, these cannot be inherited.
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Speciation
■ Micro evolution comprise of small significant changes which change the common characteristic of a particular species
■ Speciation is the formation of new species from the existing one or splitting of a population of an organism/species into two population that connot reproduce with each other and can be termed as two independent species (= Reproductive isolation)
■ Sympatric speciation involve the mechanism when a small segment of population say subpopulation become isolated reproductively and with time isolating mechanism comes intoforce, a new sub-species emerges.
■ In allopatric speciation, a part of population becomes geographically isolated from the main population, resulting in decrease in the level of gene flow and over generation give rise to a new species.
■ Over generations, genetic drift will accumulate different changes in each sub-population.Natural selection operates differently in these different geographical locations.
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■ Genetic drift and natural selection results in these two isolated population becomes more and more different from each other eventually these two groups will be incapable of reproducing with each other and are regarded as new species.
■ Reproductive isolation can also occur if DNA changes in sex-cells are enough (as changes in number of chromosomes) and as a result there is no fusion of sex germ cells.
■ In case of fusion, a new variation evolves.
■ Genetic variations, natural selection and reproductive isolation are key factors in modern concept of evolution.
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34. How do sexual and asexual reproductions lead to speciation? Give one point for each.
Ans. (i) Sexual reproduction produces a lot of variations due to reshuffling of chromosomes and crossing over. Variations help in natural selection and speciation.
(ii) Asexual reproduction also develops variations occasionally due to errors in DNA replication. These variations help in natural selection and speciation.
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35. Define the following with the example of each
(a) Genetic drift
(b) Natural selection
(c) Reproductive isolation.
Ans. (a) Genetic Drift: It is random changes in gene frequency in small isolated population, fixing some alleles and eliminating others. Suppose, in a population of red coloured beetles, some blue coloured beetles appear due to mutation. If all the red coloured beetles are eliminated due to trampling by an elephant, the surving beetles will be all of blue colour, through blue colour has no selective advantage.
(b) Natural Selection: It is survival and preferential reproduction by those individuals which show better adaptation to existing environment. In a population of red and green beetles, crows eat more of red beetles. Green beetles are spared due to their colour which is of adaptive advantage against the background of green foliage.
(c) Reproductive Isolation: It is absence of interbreeding between members of different species. Reproductive isolation maintains the sanctity of a species. It is also basic to the 15, formation of new species from an isolated population. The latter accumulates variations that prevent mating between it and the parent population.
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36. Briefly explain the role of natural selection and genetic drift in speciation by citing an example.
Ans. Natural selection is preferential survival and differential reproduction of individuals of a population which possess variation that provides better adaptability to the existing environment In a beetle population of mostly red colour, a few green beetles appear due to variation. While red beetles are eaten by crows, the green beetles are spared. The number of green beetles will gradually rise while that of red beetles will decline and ultimately disappear. Here, natural selection is being exerted by crows resulting in a new type of beetle population.
Genetic drift is a random change in gene frequency in a small population, fixing some alleles and eliminating others. Suppose in the red beetle population some blue beetles appear due to mutation. An elephant tramples the bush and kills all the red beetles. The surviving small population of beetles will be of blue colour through it has no selective advantage.
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37. “Natural selection and speciation leads to evolution.” Justify this statement.
Ans. Natural selection (survival of fittest) is the struggle for existence, only those individual survive and reproduce which have the most useful variations. These variations are transferred to new generation. Next generation again repeat the process of formation of new variations and natural changed during the selection. Accumulations of variations produce a new species.
Speciation the formation of new species from pre-existing ones through modification/variation comprises organic evolution. Darwin (1899) has called evolution to the descent with modifications
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POINTS TO REMEMBER
■ Characteristics are the details of appearance or behaviour i.e.. a particular form or particular function e.g.. Presence of limbs, photosynthesis in plants.
■ Basic characteristics are shared by all organisms as cell is basic unit of life. Basic cell design, presence of nucleus differs in organisms i.e.. Prokaryote and eukaryotes. Eukaryotes Unicellular or multicellular, then photosynthetic or not, then skeleton inside or not.
■ Characteristics in the higher level of classification would be shared by few and so on.
■ The more characteristics two species have in common, the more closely they are related and it also indicates their common ancestry.
■ Classification of species is infact a reflection of their evolutionary relationship.
■ Small group of species with recent common ancestors then super group of these species with more distant common ancestors and so on. In the end, we come to the end with a single species at the beginning of evolutionary line. It will be some point in history of earth where non-living organisms must have given rise to life
■ Characteristic in different organisms would be similar because they are inherited from a common ancestor.
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■ All amphibian, reptiles, birds and mammals have similar basic structure of limbs, though relationship. C they are modified to perform the different functions in vertebrate. Thus are called homologous organs.
■ All similarities in organ shapes may not be a indicators of common ancestor. For example wings of birds and bat, squirrels and lizard do not have. So, birds and bats more closely related to each not so. Because wings of bats are skin fold stretched between elongated fingers and wings of birds are a feathery covering all along the arm. The components are thus very different through they are performing same functions are called analogous organs.
■ All the remnants of hard body parts or the impression of the past living organisms, preserved in the earth are called fossils.
■ Fossils found closure to surface are more recent, than fossils found in deeper layers.
■ Dating fossils i.e. Determining the age of fossil can be done by detecting the ratio of different isotopes of the same elements in the fossil material.
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■ The complicated organs evolved by changes, over generation and not by a single DNA error/ change e.g. Eyes selected for its advantage.
■ There are intermediate stages in the development of complicated organs e.g., rudimentary eyes in Planaria detect light. Insects, octopus and vertebrates eyes differ in their structure and have separate evolutionary origin
■ A change useful to one function can later becomes useful for a quiet different function e.g. Development of feather initially was to provide insulation in cold weather but later became useful for flight. For example some dinosaurs had feathers not for flight but birds adapted the feather to fight. It indicates similarities of birds to reptiles.
■ Human beings have developed different varieties of cabbage plant by artificial selection of traits which are useful to them. The artificial selection was for different traits/purpose i.e., condensed internodes compact structure-cabbage or arrested flower development (broccoli) or for sterile flowers (cauliflower) or swollen parts (Kohlrabi) or for slightly large leaves (Kale). All these different varieties have developed from wild cabbage.
■ Comparing the DNA of different species gives a direct estimate of how much DNA has changed during the formation of species.
■ Molecular phylogeny tells us that the organisms, which are more distantly related will accumulate a great differences in their DNA
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38. Give an example of the characteristics being used to determine how close two species are in evolutionary terms.
Ans. The more common characteristics two species have, the more closely they are related. The more closely two species are related, the more recent will be their common ancestors. Tiger and leopard are closely related species. They have evolved from a common recent ancestor. They are related to dogs but in fewer common characteristics and had a distinct common ancestor.
39. What are fossils? How do they act as an evidence for organic evolution?
Ans. Fossils are remaining traces and impression of past organisms. With the discovery of fossil of Archaeopteryx, it has been established how the birds arose from reptiles. Prior to Archaeopteryx feathers have already evolved in dromaeosaurs for protecting them from cold.
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40.”Evolution and classification of organisms are interlinked.” Give reason to justify this statement.
Ans. Classification is the arrangement of organisms into groups and sub groups on the basis of similarities and dissimilarities and placing them in a hierarchy that brings out their evolutionary relationship. Characteristic may be physical, physiological and behaviourstic. They may be ancestral or basic (parts of basic body design present in all the members of the group) or derived (developed due to evolutionary changes in ancestral characteristic). They determine sub-group of organisms. Further changes in derived characteristic produce new feature that gives rise to smaller sub-groups. Thus evolution and classification are interlinked.
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41. Name two homologous structures in vertebrates. Why are they so called? How these organs help in Understanding an evolutionary relationship?
Ans. Paddle of whale and wings of a bird are two homologous organs which similar basic plan and internal structure. They are externally quite dissimilar and perform different functions, swimming in whale and flying in bird. Their similar internal structure points to their common ancestry. Modification or evolution occurred in them to produce present forms.
42.What are fossils? How do they tell us about process of evolution?
Fossils They are remains or impression of past organisms that lie burried in the rocks and other structures belonging to various ages.
Fossils Indicate Evolution
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1. Different types of organisms appeared in different ages. Many of them have later on disappeared. Some gave rise to other organisms while a few are persisting even now.
2. Early forms were simple. Most of the later forms become more and more complex.
3. Fossils of different ages indicate the path of evolution, e.g., fishes → amphibian → reptiles → Birds → Hammials
4. Some fossils have characteristics intermediate between two groups, e.g., Archaeopteryx between reptiles and birds. They indicate the path of evolution.
5. Phylogeny of some organisms has been worked out with the help of fossils e.g., Horse.
42. State how evolutionary relationship can be traced by the study of homologous organs.
Ans. Homologous organs have similar internal body plan and anatomy. Fore limbs of all tetrapods have pentadactyl structure being made of humerus, radioulna, carpals, metacarpals and phlanges. However, they perform different functions in different tetrapods like absorbing shock of jumping of Frog, creeping in lizard, flying in birds or grasping in humans. These organs clearly indicate a common ancestry from which different modifications occurred that suited them in their habitats.
43. An organ like wings is an advantage to the organism. Did it appear in the different stages or was formed due to single sudden change. (Understanding based question) (C.C.E. 2014)
Ans. Organs like wings appeared in different intermediate stages and not through sudden change. Wings were preceded by feather in small extinct dinosaurs called dromaesaurs. They are also present on the fore limbs. The feathered for limbs helped the small animals in long jumps. It was followed by gliding and then flying.
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POINTS TO REMEMBER
■ In evolution, it is not so that the old species will disappear. It depends upon environment.
■ It is also not true that newly generated species are in any way better than the old one.
■ Natural selection and genetic drift have together led to the formation of a new population that cannot reproduce with the older one.
■ Human beings and chimpanzees do not have a common ancestor, human nor do chimpanzees like. Both human and Chimpanzees evolved in their own separate ways to give rise to modern form.
■ To sum up evolution is simply the generation of diversity and the shaping of diversity by environmental selection. Progressive trend in evolution led to move complex forms, however old, simple designs also persist.
■ Simplest life forms bacteria have mastered all types of inhospitable habitats.
■ Human beings do not represent the end of evolution but another species in the vast world of living organisms where life is evolving continuously since its origins
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■ Study of human evolutions have been possible due to excavating, time dating and studying fossils from the different continents of the world.
■ These is a great diversity in human forms and features.
■ Skin colour is the common way of identifying the human races e.g., yellow, black, white, brown etc.
■ Biological, all humans are a single species.
■ All humans have their origin in Africa.
■ Some of our ancestor left Africa thousand years ago and few stayed back, the migrants slowly spread across from Africa to west Asia, then to central Asia Eurasia, South Asia, East Asia and then to America.
■ Like other species, human beings exist as an accident of evolution.
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44. What is an organic evolution? It cannot be equated with progress. Explain with the help of a suitable example.
Ans. In tracing the family trees of species there are certain facts such as there are multiple branches at each and every stage of process and when a new species emerge the old species survival or elimination depends upon the environment. It is not that newly generated species in any way better than the old one. It is just that natural selection and genetic drift have together led to the formation of a population that cannot reproduce with the original one. For example; it is not true that human beings have evolved from chimpanzee but both have a common ancestor long ago. The two resultant species probably evolved in their own separate ways to give rise to the modern forms.
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Actually, there is no progress in the idea of evolution. Evolution is simply the generation of diversity and the shaping of diversity by environmental selection. The only progresses is the emergence of more and more complex body designs over a very long period, along with the persistence/retention of old designs. In fact, the old designs of simple life forms such as bacteria are not inefficient but are perfectly adapted to the inhospitable habitats. In other words, human beings are not top of evolution but they are like the other species representing life forms. Thus evolution does not processed as “ladder of progress but” occurs as branches of trees.
45. Why are human beings who look so different from each other of size, colour and looks said to belong to the same species?
Ans. On the basis of time dating, study of fossils and molecular phylogency involving DNA sequences, all the human races belong to a single species Homo sapiens. Moreover, all the individual of this species can interbreed freely to produce the fertile offspring.
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46. How does the creation of variations in a species ensure survival?
Ans. Variations in a species arise either due to errors in DNA copying or during sexual reproduction. Force of natural selection selects individuals with useful variations in the prevailing environment so as to ensure their survival. The individuals with useful variations then increase in number through differential reproduction in the population.
47. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Ans. Animals show vast diversity in structure. They probably do have a common ancestry. It is so because common ancestry cannot lead to such a vast diversity. Also, evolution of these diverse animal forms in the same habitat is also not likely by geographical isolation and speciation.
48 Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
Ans. It is a debatable issue. Bacteria have simple life forms, oldest and simpler design for survival depend on the environment. If we consider progressive trends complexity in structures vis-a-vis evolution, human beings are definitely more evolved than bacteria.
49. All the human races like Africans, Asians, Europeans, Americans and other might have evolved from a common ancestor. Provide few evidences in support of this view.
Ans. (i) These human races have similar body plan, structure, physiology and metabolism.
(ii) These have same chromosome number.
(iii) These freely inter-breed among themselves.
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