CBSE Class 10 Science Chapter 9 Heredity And Evolution
Heredity:
CBSE Class 10 Science Chapter 9 Heredity And Evolution Short Question And Answers
Question 1. If trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer: Trait B has arisen earlier.
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Question 2. How does the creation of variations in a species promote survival?
Answer:
Variations occur in a species due to inaccurate copying of DNA and also due to sexual reproduction. Depending on the nature of variations, different individuals would have different kinds of advantages.
- For example, bacteria variants which can withstand heat have better chances to survive in a heat wave than non-variant bacteria that cannot tolerate heat waves.
- Thus, variations in the population of a species help in the survival of a species. However, at the individual level, variants which are not suitable to the prevailing environment may not survive.
Question 3. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
The trait which appears in all the members of the F1 generation and also in 75% of members of the F2 generation, obtained by self-fertilisation of the F1 generation, is the dominant character.
The trait which does not appear in the F1 generation but after self-fertilisation of the F1 generation reappears in 25% of the F2 generation is known as recessive character.
Question 4. How do Mendel’s experiments show that traits are inherited independently?
Answer:
If pea plants with two different pairs of characteristics (e.g., tall dwarf and round seeds/ wrinkled seeds) are bred with each other, the F, progeny would have all tall plants with round seeds.
- This implies that round seed is a dominant character over wrinkled seed. In F2 progeny there would be some tall plants with round seeds and short plants with wrinkled seeds.
- However, there would be some plants with mixed characteristics plants with wrinkled seeds and short plants with rough seeds.
This depicts that tall/dwarf traits and round/wrinkled traits are inherited independently of each other (law of independent assortment). The following Punnett square explains this:
Parents: TTRR × torr
F1: Tt Rr
F2:
Phenotypic ratio: Tall round: Tall wrinkled: Dwarf round: Dwarf wrinkled = 9:3:3:1 3.
Question 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 traits group A or O is dominant? Why or why not?
Answer:
The information is not enough to infer which trait, blood group A or O, is dominant.
Reason:
- If A is considered to be dominant over O, then possible combinations are— Male AO and Female OO.
- Thus, the daughter can be OO and hence has blood group O.
- If O is supposed to be dominant over A then the following combinations are possible- Male AA and Female OO or OA.
In this case, the daughter can be OA and hence has blood group 0.
Thus, from the information given, we cannot ascertain which blood group is dominant.
Question 6. How is the sex of the child determined in human beings?
Answer:
The sex of the child in human beings is genetically determined. All children inherit X sex chromosomes from their mothers regardless of whether they are boys or girls.
The sex of the children is determined by what sex chromosome they inherit from their father. A child who inherits an X chromosome from a father would be a girl, and one who inherits a Y chromosome from a father would be a boy.
Question 7. What are the different ways in which individuals with a particular trait may increase in a population?
Answer:
The different ways in which individuals with a particular trait may increase in a
population are:
- Natural selection of some variants: Natural selection provides chances for certain variations that are suitable to changing environments.
- Genetic drift: Accidents/migration of members of a small population also cause an increase in individuals having particular traits. However, genetic drift does not provide a survival advantage.
Question 8. Why are traits acquired during the lifetime of an individual, not inherited?
Answer:
Changes that occur in germ cells and DNA are only transmitted from one generation to the next generation. Changes/traits in non-reproductive tissues acquired in a lifetime are not passed to the next generation.
Question 9. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:
- The small number of members in a population of tigers does not allow a large number of variations to occur which are essential to the survival of the species.
- A deadly disease or calamity may cause the death of all the tigers. The small number of tigers also indicates. that existing tiger variants are not well adapted to the existing environment and may extinct soon.
Question 10. What factors could lead to the rise of a new species?
Answer:
The factors that can lead to the rise of a new species are:
- Natural selection.
- Changes in several chromosomes or changes in genes/genes.
- Geographical isolation.
- Reproductive isolation.
Question 11. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer:
No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offspring leaving no chance of speciation.
However, geographical isolation works as a major factor in cross-pollinated species, as it would result in the accumulation of variation in the two geographically separated populations.
Question 12. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, asexually reproducing organisms have very little variation over generations. Any change resulting from geographical isolation may not be passed on to the next generation. These variations in DNA are not enough to raise a new species.
Question 13. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:
- Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers. Later on, birds adapted the feathers to flight. This means that birds are very closely related to reptiles since dinosaurs were reptiles.
- Another method to find out how close two species are in evolutionary terms is by comparing the DNA of different species. It provides a direct estimate of how much the DNA has changed during the formation of the new species.
Question 14. Can the wings of a butterfly and the wings of a bat be considered homologous organs? Why or why not?
Answer:
No, because the wings of the bat are entirely different in respect of structure, origin and plan from the wings of a butterfly. Wings of bats are modified fore-limbs which have bones and skin, whereas the wings of butterfly do not have bones.
However, wings in both species perform similar functions, so they are analogous organs and not homologous organs
Question 15. What are fossils? What do they tell us about the process of evolution?
Answer:
Preserved remains and imprints of ancient plants and animals are called fossils. Fossils tell us about the following:
- Organisms that lived long ago.
- The structure of ancient organisms and the period during which they lived.
- Evolutionary relations among organisms.
- The organisms become more complex in the upper strata when compared to the lower strata. It indicates the evolutionary process.
- Connecting links between different species. For example, Archaeopteryx exhibits an intermediate link between reptiles and birds.
Question 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?
Answer:
Although the genetic makeup of humans may be slightly different in different races of people, there is no reproductive isolation. Different species cannot breed and produce fertile progeny.
In the case of human beings, individuals different in size, colour and looks can marry among themselves and produce fertile offspring. So, they are clubbed in the same species Homo sapiens.
Question 17. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer:
Evolution does not mean progress. Evolution causes the generation of diversity and the shopping of diversity by environmental selection. Due to evolution, more and more complex body designs have emerged over time and this has been considered a progressive trend.
- It does not mean older and simpler body designs are inefficient and complex body designs like spiders, fish and chimpanzees have better body designs. Many of the older and simpler body designs still survive.
- For example, bacteria have simpler body forms, and are found in the most inhospitable habitats like hot springs, deep sea and the ice in Antarctica.
- Thus, bacteria, spiders, fish and chimpanzees are simple species in the teaming spectrum of evolving life. All the organisms which exist have a body design that is good as it is suited to their environment.
Question 18. 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?
Answer:
The information given in the question is not sufficient to infer that the light eye colour trait is dominant or recessive.
Reason: It is just possible that the parents are homozygous for the light eye colour trait. Even though it is a recessive trait, it has appeared in all of their children. Both of the parents contributed the same recessive allele.
Question 19. How are the areas of study evolution and classification—interlinked?
Answer:
- Evolutionary relationships are traced in the classification of organisms. For the classification of organisms, we look for similarities among organisms which allows us to group them. The more characteristics two species will have in common, the more closely they are related.
- It indicates that the more closely two species are related, the more recently they would have had a common ancestor. Thus, the classification of species is a reflection of their evolutionary relationship.
Question 20. Explain the terms analogous and homologous organs with examples.
Answer:
- Analogous organs: The organs which perform similar functions in different organisms but are different in structure and origin are called analogous organs For example, the wings of a bird and the wings of an insect.
- Homologous organs: The organs which perform different functions in different organisms but have similar structure, origin and components, are called homologous organs. For example, the forelimbs of a frog, the front legs of a horse, the wings of a bird, hands of human beings (all are modified forelimbs performing different functions).
Question 21. Outline a project which aims to find the dominant coat colour in dogs.
Answer:
- Select a black homozygous male dog and a white homozygous female dog. Allow them to mate. Observe their progeny (F1 generation).
- If all members of the F1 generation have black coats, then the black colour coat is dominant. If the progeny has a white coat then a white colour coat is dominant.
Question 22. Explain the importance of fossils in deciding evolutionary relationships.
Answer:
Fossils provide us evidence about:
- The organisms that lived long ago such as the period during which they lived, their structure etc.
- Evolutionary development of species i.e., line of their development (phylogeny of organisms).
- Connecting links between two groups. For example, feathers present in some dinosaurs (reptiles) means that birds are very closely related to reptiles.
- Which organisms evolved earlier and which later?
- Development of complex body designs from simple body designs.
Question 23. What evidence do we have for the origin of life from inanimate matter?
Answer:
Experiments conducted by Stanley L. Miller and Harold C. Urey in 1953 provide some light on the origin of life from inanimate matter.
- They assembled an atmosphere similar to that thought to exist on early Earth (that had molecules like ammonia (NH3), methane (CH4) and hydrogen sulphide but no oxygen) over water.
- They maintained the mixture of these gases just below 100°C and passed sparks to simulate lightning.
- At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.
- It indicates the possibility of the origin of life from inanimate matter on the earth, when the atmosphere was reducing (containing no free oxygen), containing gases like methane, ammonia, and hydrogen sulphide; frequent lightning and enough water was present.
- Simple amino acids which are building blocks of proteins might have given rise to complex molecules that are building blocks of cells.
The origin of life from inanimate matter is not at all possible today because:
- The atmosphere contains free oxygen (oxidising) which causes breakdown of molecules necessary for the origin of life.
- The conditions which existed on early Earth cannot be regenerated.
Question 24. 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?
Answer:
Sexual reproduction causes more viable variations due to the following reasons:
- Error in copying of DNA, which is not highly significant.
- Random segregation of paternal and maternal chromosomes at the time of gamete formation.
- Exchange of genetic material between homologous chromosomes during formation of gametes.
- Accumulation of variations occurred due to sexual reproduction over generation after generation and selection by nature created wide diversity.
In the case of asexual reproduction, only very small changes due to inaccuracies in DNA copying pass on to progeny. Thus, offspring of asexual reproduction are more or less genetically similar to their parents.
So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.
Question 25. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
When round and green seeded crossed with wrinkled and yellow seeded pea plants, F1 generation has obtained round and yellow seeds. F1 generation when self-fertilised shows four types of plants:
- Round and yellow
- Wrinkled and yellow
- Round and green
- Wrinkled and green.
If we interpret this result that indicates both parents must be contributing equally to the DNA of the progeny during sexual reproduction.
If both parents can help determine the trait in the progeny, both parents must be contributing a copy of the same gene. It means a member of progeny must have two sets of all genes, one inherited from each parent.
Question 26. 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?
Answer:
No, it depends on the nature of variations, different individuals have different kinds of advantages. When drastic changes occur in the environment only those organisms of the population will survive which have favourable variations.
Question 27. Variations are important for the survival of species over time. Justify this statement with reasons.
Answer:
- It causes adaptations.
- It promotes natural selection.
Question 28.
- Which type of organs are shown in the figure below?
- Which type of origin and structure do these organs have?
Answer:
- These are organs which help in flying (wings of insects and wings of birds).
- The structure and components of these wings are different. They look similar because they have a common use for flying, but their origins are not common, i.e., they are analogous.
Question 29. Define F1 and F2 generations.
Answer:
F1 or first filial generation is the generation of hybrids derived from a cross between two genetically different homozygous individuals.
F2 or second filial generation is the generation produced as a result of interbreeding between individuals of the F1 generation.
Question 30. “It is a matter of chance whether a couple will give birth to a male child or a female child.” Justify this statement with the help of a flow chart showing the fusion of sex chromosomes.
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Since the sperms carry an ing ‘X’ chromosome and sperms carry an ing Y chromosome have an ave equal/50-50 chance of fertilizing an egg, thus it is a matter of chance whether a couple will give birth to a male or a female child.
Question 31. What function is performed by human arms, the forelimbs of dogs and the forelimbs of whales?
- Which type of organs are these?
- Why do we call them so?
Answer:
- Human arm: holding things Forelimbs of dog: running Forelimbs of whales: paddles
- Homologous
- Same origin, and different functions.
Question 32.
- How many gene sets should a germ cell have?
- Mention two factors causing evolution.
Answer:
- One gene set
-
- Reproduction isolation
- Natural selection
Question 33.
- “Recent fossils are found closer to the earth’s surface.” Comment on the statement state the ing reason.
- List two factors which could lead to the rise of new species.
Answer:
- This statement is correct as the fossils found closer to the surface of the earth are more recent and those found in deeper layers are older ones.
- Natural selection and genetic drift.
Question 34. “Experiences of an individual during its lifetime cannot be passed on to its cannot direct evolution”. Justify this statement ent giving an example.
Answer:
Since acquired characteristics are not inherited over generations, changes in non-reproductive tissues cannot be passed on to the DNA of the germ cells.
Question 35. In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Sehaj Anant obtained only tall plants denoted by Tt in the F1 generation. However, in the F2 generation, she obtained both tall and short plants. Using the above information explain the law of dominance.
Answer:
According to the law of dominance, the dominant trait gets expressed in the F, generation.
Although both the dominant and the recessive traits get inherited in the F generation, it is only the dominant trait which gets expressed, i.e., a single copy of the dominant trait is enough for the expression of the tall traits traitrait like “T’ is thus cala-led dominant trait.
Question 36. If YYRR is Round yellow, what do the following represeyouryyyyyRR
Answer
- your – Wrinkled, green eye – Round, green seeds
Question 37. What is the importance of DNA copying in reproduction? Why is variation beneficial to the species but not necessary for the individual? Explain.
Answer:
DNA copying is an essential part of reproduction because it ensures that the same blueprint of the body design is maintained. Variation for the species is beneficial for adaptation and better survival. It may result in new species formation.
Question 38. If a population of red beetles, living on green bushes, is being eaten by crows. During sexual reproduction, a green beetle is found in progeny:
- What is the future of new traits?
- Will it survive in the new habitat?
Answer:
- Among progeny, when a green beetle is found, it escapes the attack of crows as it merges with a green colour. Green beetles increased, red decreased.
- traitsrait will survive.
Question 39. An angiosperm plant having red coloured flowers when crossed with the other having the same colour produced 40 progenies, out of which 30 plants were with red coloured flowers, and 10 plants were with white coloured flowers. Find out:
- What is the possible genotype of parent plants?
- Which trait is dominant and which is recessive?
- What is this cross called and what is its phenotypic ratio?
Answer:
- Rr and Rr.
- The red colour of the flower is the dominant trait while the white colour is the recessive trait.
- Monohybrid cross, phenotypic ratio is 3: 1.
Question 40. The modern human beings have originated in Africa.
- What evidence suggests this fact?
- If an animal is similar to its ancestors, what does it imply?
Answer:
- Discovery of fossils in AfriOrganismsnism is recently evolved fancestorsstAnimalsimal has not accumulated variations.
Question 41.
- What is the genetic constitution of human sperm?
- Mention chromosomeomes pair present in zygote determining the sex of a male child.
Answer:
- 22+ Y or 22+ X
- (22 + Y + 22+ X)
Question 42.
- Wrthe ite full form of DNA.
- Why are variations essential for the species?
Answer:
- Deoxyribonucleic Acid
- For survival.
Question 43. Where are the genes located? What is the chemical nature of genes?
Answer:
Genes are located on chromosomes in linear sequence and at fixed positions. Chemically, genes are accurate since they are nucleic acids which constitute DNA.
Question 44.
- In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Preeti obtained only tall plants denoted by Tt in the F1 generation. However, in the 2 generations, she obtained both tall and short plants. Using the above information explain the law of dominance.
- What is genetic drift?
Answer:
- According to the law of dominance trait that is dominant gets expressed in the F1 generation. Although both the dominant and the recessive traits get inherited in the F1 generation, it is only the dominant trait which gets expressed, i.e., a single copy of the dominant trait is enough for the expression of the tall trait. Traits like “T” are thus called dominant traits.
- Accidents in a small population can change the frequency of some genes in a population although they give no survival advantage. This is called genetic drift.
Question 45. Differentiate between:
- Homologous organs and Analogous organs
- Pollination and Fertilisation
- What do fossils tell us about the process of evolution?
Answer:
- Organs in different organisms have the same origin with different functions/differoriginsigin, same function.
- Transfer of pollen from the stamen to the pistil of the flower/Fusion of male and female gametes.
- Help in establishing links and act as evidence of evolution.
Question 46.
- Place the following in the correct sequence: Natural selection / Migration/New species/ Gene flow.
- Evolutions of cauliflower, broccoli, cabbage ge, and red cabbage are all forms of wild cabbage. Is this an example of natural selection or artificial selection?
Answer:
- Migration/Gene flow/Natural selection/New species.
- Artificial selection.
Question 47.
- State any two factors that could lead to the rise of a new species.
- How do analogous organs provide evidence in favour of evolution?
Answer:
- Natural Selection, Genetic drift, Mutations, Variations.
- The organs which are similar in function but are structurally different suggest that although these two organs may look alike superficially giving an idea of common ancestry the difference in structure and origin suggests that organisms having these organs have a distant ancestor but such organs have developed during evolution as an adaptation to a similar mode of life.
Question 48. In plants round seed is dominant over the wrinkled. If a cross is carried between these two plans answer the following questions:
- Mention the genes for the traits of parents.
- State the trait of F1 hybrids.
- Write the ratio of F2 progeny obtained from this cross. What is the name of the cross?
Answer:
- R/rr
- Rr/hybrid Round
3:1
1:2:1
Monohybrid cross.
Question 49.
- State the term given to the structure shown in figures given b.low.
- State the evolutionary evidence obtained from such structures.
- Why are traits acquired during the lifetime of an individual, not inherited
Answer:
- Homologous orgaThe basic structures of limbs same, but function differently.
- The similarities indicate that all these vertebrates had common ancestors.
- Change in non-reproductive tissues cannot be passed to germ cells.
Question 50.
- Name the scientist who worked out the rules of inheritance.
- Mention any two strategies that are used by different species for determine ing sex of their newborns.
Answer:
- Mendel
- Some rely on environmental cues. In some ani, mals the temperature at which a fertilized egg is kept determines its sex. In snails, individuals can change sex, indicating that sex is not genetically determined.
Question 51. Give appropriate terms for the following:
- The trait which can express itself in the next generation.
- The trait an organism has due to inheritance.
- Origin of a new species from a pre-existing one.
Answer:
- Dominant trait
- Inherited trait
- Speciation
Question 52.
- What are fossils?
- Explain the importance of fossils in evolutionary relationship
Answer:
- Impressions of the body parts of the organisms and preserved traces of the living organisms are called fossils.
- The presence of fossilized remains of the organisms is the evidence of existence of organisms millions of years ago which have now become extinct. Fossils also help in determining the connecting links between various groups and their origin from their primitive ones.
Question 53.
- Name the scientist who gave the idea of the evolution of species by natural selection.
- What conclusion did Mendel draw from his experiments about traits?
- Arrange the following according to evolution.
Cockroach, Mango tree, Gorilla, Fish
Answer:
- Darwin.
- Traits are inherited independently.
- Mango tree-Cockroach-Fish-Gorilla.
Question 54.
- Explain why the wing of a bat and the wing of a bird are considered to be analogous organs
- List two factors that lead to the formation of a new species.
Answer:
- Design, structure and components are different. Origins are not common.
- Genetic drift and natural selection.
Question 55. How do different races of human beings belong to the same species?
Answer:
- By using various tools such as excavation, time-dating and studying fossils as well as determining DNA sequences to study human evolution, it is evident that there is no biological basis to the notion of the human race. All humans are a single species.
- It is established by scientific studies that all human races belong to a human species called Homo sapiens. That een evolved in Africa and spread across the world in stages.
Question 56. How is the sex of a newborn determined in humans?
Answer:
The sex of the individual is genetically determined i.e., genes inherited from parents decide whether the newborn will be a boy or a girl. A newborn who inherits an ‘X’ chromosome fa from a father will be a girl and one who inherits a Y chromosome from a father will be a boy.
Question 57. Does the genetic combination of mothers play a significant role in determining the sex of a newborn?
Answer:
No, because mothers have a pair of X chromosomes. All children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls.
Question 58. Mention three important features of fossils which help in the study of evolution.
Answer:
- Fossils represent modes of preservation of ancient species.
- Fossils help in establishing evolutionary traits among organisms and their ancestors.
- Fossils help in establishing the period in which organisms lived.
Question 59. Why do all the gametes formed in human females have an X chromosome?
Answer:
Human females have two X chromosomes called sex chromosomes. During meiosis at the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes possess an X chromosome.
Question 60. In human beings, the statistical probability of getting either a male or a female child is 50:50. Give a suitable explanation.
Answer:
The sex of an infant is determined by the type of sex chromosome contributed by the male gamete. Since the ratio of male gametes containing the X chromosome and those containing the Y chromosome is 50: 50, the static probability of male or female infant is 50: 50.
Question 61. A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Answer:
Fewer individuals in a species impose extensive inbreeding among them. This limits the appearance of variations and puts the species at a disadvantage if there are changes in the environment. Since the individuals fail to cope with the environmental changes, they may become extinct.
Question 62. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Answer:
Structures which have a common basic structure but perform different functions are called homologous structures, e.g. fore-limbs of reptiles, amphibians and mammals. Yes, they have a common ancestor but they are variously modified to carry out different activities.
Question 63. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Answer:
- Though animals have a vast diversity in structures they probably do not have a common ancestry, because common ancestry may greatly limit the extent of diversity.
- As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animals is not the likely theory.
Question 64. Give the pair of contrasting traits of the following characters in the pea plant and mention which is dominant and recessive
- Yellow seed
- Round seed
Answer:
Question 65. Why did Mendel choose the pea plant for his experiments?
Answer:
- Easy to grow
- Short life span
- Easily distinguishable character larger gear size of flower
- Self-pollinated
Question 66. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Answer:
- The woman produces ova with ‘X’ chromosome.
- The man produces sperm with X and Y chromosomes which determines the sex of the baby.
Question 67. What are the three ways which can produce variant genotypes in the environment?
Answer:
- Gene mutations
- Crossing over
- Hybridisation
Question 68. Give reasons for the appearance of new combinations of characters in the F2 progeny.
Answer: The tall/short and round/wrinkled seed traits are independently inherited.
Question 69. The genotype of green stemmed tomato plant is denoted as GG and that of purple stemmed tomato plant as gg. When are these two crossed?
- What colour of stem would you expect in their F1 progeny?
- Give the percentage of purple-stemmed plants if F1 plants are self-pollinated.
- In what ratio would you find the genotypes GG and Gg in the F2 progeny?
Answer:
- Green (as G denotes the dominant gene and is expressed in all plants of F1 generation.)
- 25% of F2 generates ions raised by self-pollinated F plants.
- GG-25%
Gg-50%
Thus, the ratio is 1:2 in F2 progeny.
Question 70. Guinea pigs having black colour when crossed with guinea pigs having the same colour produced 80 offspring, out of which 60 were black and 20 were white. Now, find out:
- What is the possible genotype of the guinea pig?
- Which trait is dominant and which trait is recessive?
- What is this cross called and what is its phenotypic ratio?
Answer:
- Bb x Bb
- Black is dominant while white is recessive.
- Monohybrid cross Phenotypic ratio = 3:1
Question 71. In a quarry of sandstone, a digger found some bones below the rocks. He took them out and was about to throw them away when his fellow digger told him that this could be a fossil and they should hand it over to the museum.
Answer the following questions based on the above situation:
- Which values are promoted by the fellow digger?
- What contributions are the diggers making to the scientific world?
- Imagine yourself to be the person in the museum whom the diggers approach. What would be your response to the diggers’ discovery?
Answer:
- Rational thinking, awareness, preservation of heritage.
- They provided a link which can help scientists to study the process of evolution and know more about the world, in which humans did not exist.
- I would take the bone samples and send them for carbon dating to find which period they belong to.
Question 72. A group of class X students prepared a street play to educate ate masses on gender disparity to the top sex determination of a girl child and abort it.
- In human beings, what is the chance of giving birth to a girl child?
- Who is responsible for the birth of a female child and why?
- What value is depicted among the group members of class X?
Answer:
- The chance of giving birth to a girl child is 5The male-male is responsible because only the male individual is a carrier of X and X chromosomes.
- The group members show teamwork, collaborative leadership and participating citizenship.
Heredity And Evolution Multiple Choice Questions
Question 1. The exchange of genetic material takes place in
- Vegetative reproduction
- Asexual reproduction
- Sexual reproduction
- Budding
Answer: 3. Sexual reproduction
Question 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
- Double fertilisation
- Self-pollination
- Cross fertilisation
- No fertilisation
Answer: 2. Self-pollination
Question 3. A cross between a tall plant (TT) and a short pea plant (tt) resulted in progeny that were all tall plants because
- Tallness is the dominant trait
- Shortness is the dominant trait
- Tallness is the recessive trait
- The height the of pea plant is not governed by gene ‘T’ or ‘t’
Answer: 1. Tallness is the dominant trait
Question 4. Which of the following statements is incorrect?
- For every hour, mone there is a gene.
- For every pro, then there is a gene.
- For the production of every enzyme, there is a gene.
- For every molecule of, fat there is a gene.
Answer: 4. For every molecule of fat there is a gene.
Question 5. If a round, green-seeded pea plant (RRyy) is crossed with a wrinkled, yellow-seeded pea plant (rrYY), the seeds produced in the F1 generation are
- Round and yellow
- Round and green
- Wrinkled and green
- Wrinkled and yellow
Answer: 1. Round and yellow
Question 6. In human males, all the chromosomes are paired perfectly except one. This / these unpaired chromosome is/are
- large chromosome
- small chromosome
- Y-chromosome
- X-chromosome
- 1 and 2
- 3 only
- 3 and 4
- 2 and 4
Answer: 3. 3 and 4
Question 7. The maleness of a child is determined by
- The X chromosome in the zygote
- The Y chromosome in zygote
- The cytoplasm of germ cell determines the sex
- Sex is determined by chance
Answer: 2. The Y chromosome in a zygote
Question 8. A zygote which has an X-chromosome inherited from the father will develop into a
- Boy
- Girl
- X-chromosome does not determine the sex of a child
- Either boy or girl
Answer: 2. Girl
Question 9. Select the incorrect statement
- The frequency of certain genes in a population changes over several generations resulting in the evolution
- Reduction in weight of the organism due to starvation is genetically controlled
- Low-weight parents can have heavy-weight progeny
- Traits which are not inherited over generations do not cause evolution
Answer: 2. Reduction in weight of the organism due to starvation is genetically controlled
Question 10. New species may be formed if
- DNA undergoes significant changes in germ cells
- Chromosome number changes in the gamete
- There is no change in the genetic material
- Mating does not take place
- 1 and 2
- 2, 3 and 4
- 1 and 3
- 1, 2 and 3
Answer: 1. 1 and 2
Question 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 a new combination of characters. Choose the new combination from the following
- Round, yellow
- Round, green
- Wrinkled, yellow
- Wrinkled, green
- 1 and 2
- 1 and 4
- 2 and 3
- 1 and 3
Answer: 2. 1 and 4
Question 12. A basket of vegetables contains carrots, potatoes, radishes and tomatoes. Which of them represent the correct homologous structures?
- Carrot and potato
- Carrot and tomato
- Radish and carrot
- Radish and potato
Answer: 3. Radish and carrot
Question 13. Select the correct statement
- Tendril of a pea plant and phylloclade of Opuntia are homologous
- The Tendril of a pea plant and the phylloclade of Opuntia are analogous
- Wings of birds and limbs of lizards are analogous
- Wings of birds and wings of bats are homologous
Answer: 1. Tendril of a pea plant and phylloclade of Opuntia are homologous
Question 14. If the fossil of an organism is found in the deeper layers of the earth, then we can predict that
- The extinction of organisms has occurred recently
- The extinction of organisms occurred thousands of years ago
- The fossil position in the layers of the earth is not related to its time of extinction
- The time of extinction cannot be determined
Answer: 2. The extinction of organism has occurred thousands of years ago
Question 15. Which of the following statements is not true concerning variation?
- All variations in a species have an equal chance of survival
- Change in genetic composition results in variation
- Selection of variants by environmental factors forms the basis of evolutionary processes
- Variation is minimal in asexual reproduction
Answer: 1. All variations in a species have an equal chance of survival
Question 16. A trait in an organism is influenced by
- Paternal DNA only
- Both maternal and paternal DNA
- Maternal DNA only
- Neither by paternal nor by maternal DNA
Answer: 3. Maternal DNA only
Question 17. Select the group which shares the maximum number of common characters
- Two individuals of a species
- Two genera of a family
- Two species of a genus
- Two genera of two families
Answer: 1. Two individuals of a species
Question 18. According to the evolutionary theory, the formation of a new species is generally due to
- Sudden creation by nature
- Accumulation of variations over several generations
- Clones formed during asexual reproduction
- Movement of individuals from one habitat to another
Answer: 2. Accumulation of variations over several generations
Question 19. From the list given below, select the character which can be acquired but not inherited
- Colour of eye
- Colour of skin
- Size of body
- Nature of hair
Answer: 3. Size of body
Question 20. The two versions of a trait (character) which are brought in by the male and female gametes are situated on
- Copies of the same chromosome
- Two different chromosomes
- Sex chromosomes
- Any chromosome
Answer: 1. Copies of the same chromosome
Question 21. Select the statements that describe the characteristics of genes
- Genes are specific sequences of bases in a DNA molecule
- A gene does not code for proteins
- In individuals of a given species, a specific gene is located on a particular chromosome
- Each chromosome has only one gene
- 1 and 2
- 1 and 3
- 1 and 4
- 2 and 4
Answer: 2. 1 and 3
Question 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
- 1:3
- 3:1
- 1:1
- 2:1
Answer: 3. 1:1
Question 23. The number of pair(s) of sex chromosomes in the zygote of humans is
- One
- Two
- Three
- Four
Answer: 1. One
Question 24. The theory of the evolution of species by natural selection was given by
- Mendel
- Darwin
- Morgan
- Lamarck
Answer: 2. Darwin
Question 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
- Reptiles have evolved from birds
- There is no evolutionary connection between reptiles and birds
- Feathers are homologous structures in both organisms
- Birds have evolved from reptiles
Answer: 4. Birds have evolved from reptiles
Question 26. 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 makeup of the tall parent can be depicted as
- TTWW
- TTww
- TtWW
- TtWw
Answer: 3. TtWW
Question 27. An example of homologous organs is
- Our arm and a dog’s foreleg.
- Our teeth and an elephant’s tusks.
- Potato and runners of grass.
- All of the above.
Answer: All of the above.
Question 28. In evolutionary terms, we have more in common with
- A Chinese schoolboy.
- A chimpanzee.
- A spider.
- A bacterium.
Answer: A Chinese schoolboy.
Hint: A Chinese schoolboy is a Homo sapien like us.