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Heredity and Evolution Class 10 Important Questions with Answers Science Chapter 9
Heredity and Evolution Class 10 Important Questions Short Answer Type
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? (CBSE 2008)
What is the effect of DNA copying which is not perfectly accurate on the reproduction process? (AI CBSE)
If DNA copying is not perfectly accurate then the variations occurs among the species of same organisms.
Describe briefly four ways in which individual with a particular trait may increase in population. (Foreign 2008)
Four ways in which individual with a particular trait may increase in population are:
- Variations that occur in species helps in the survival of individuals.
- Organisms when show genetic drift which cope them to survive in the given environment.
- Adaptation and natural selection.
- Sexual reproduction results in variation.
“Variations that confer an advantage to an individual organism only will survive in population”. Justify. (Foreign 2008)
Variation is the difference in the characters or traits among the individuals of a species. Sexual reproduction of organisms produces variation. The variations produced in organisms during successive generations gets accumulated in the organism. The significance of variations shows up only if it continues to be inherited by the offspring for several generation.
What are fossils? What do they tell about the process of evolution? (AI 2008)
Fossils are preserved traces or remains of living organism of geological past. Fossils help to trace the racial history of organisms. Fossils found closer to the surface are more recent than fossils found in the deepest layers.
What is meant by the term speciation? List four factors which could lead to speciation. (CBSE 2012)
Speciation is the evolution of reproductive isolation among once interbreeding population.
Factors which can lead to speciation are:
- Genetic drift: Over generations, genetic drift may accumulate which leads to speciation.
- Natural selection: Natural selection may work differently in different location which may give rise to speciation.
- Severe DNA change.
- A variation may occur which does not allow sexual act between two groups.
A blue colour flower plant denoted by BB is cross breed with that of white colour flower plant denoted by bb.
(a) State the colour of flower you would expect in their F1 generation plants.
(b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny. (CBSE 2012)
(a) The colour of all the flowers in Fa generation will be blue.
(b) Percentage of white flower plants in F2 generation will be 25.
(c) The ratio of genotype BB and Bb in F2 progeny will be 1 : 2.
Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason. (CBSE 2012)
- The organs have same structure but different function.
- Eg. Limbs of frog, bat and man are same in structure
- The organs have different structure but same function.
- Eg. The wings of mosquito, birds and bat is same in function but structure
Wings of a bird and wings of a bat are analogous organs as they have different basic structural design but have similar appearance and perform similar functions.
Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement. (CBSE 2012)
Evolution is sequence of gradual changes which takes place in living organisms over millions of years to give rise to new species. Evolution does not mean progress in every case. This can be proved by example of bacteria. Bacteria are the simplest and one of the oldest organisms on the earth. Their simple body design does not make them weak. Bacteria are known to survive some of the harshest climates like volcanoes and sulfur springs.
Many animals have certain features which hamper even their routine activities. For example the branch-like horns of antelope are a handicap for them. When an antelope runs for its life there are times when its horns get entangled in branches or bushes. This results in the death of the antelope.
If we cross pure-breed tall (dominant) pea plant with pure-breed dwarf (recessive) pea plant we will get pea plants of Fx generation. If we self-cross the pea plant of F2 generation, then we obtain pea plants of F2 generation.
(a) What do the plants of F2 generation look like?
(b) State the ratio of tall plants to dwarf plants in F2 generation.
(c) State the type of plants not found in F2 generation but appeared in F2 generation, mentioning the reason for the same. (CBSE 2012)
(a) All plants of F1 generation will be tall plants.
(b) 3 : 1
(c) Dwarf trait is recessive trait which was not expressed in the F1 generation, the recessive trait gets expressed in the F2 generation after self pollination.
How are fossils formed? Describe, in brief, two methods of determining the age of fossils. (CBSE 2012)
When organisms die, their bodies decompose due to action of micro organisms. However, sometime the body or at least some parts of the body may be in such an environment that does not let it decompose completely. All such preserved traces of living organisms are called fossils. The age of fossils can be’estimated by the following two methods.
- If we dig into the earth and start finding fossils, it can be assumed that the fossils closer to the surface are more recent to those found in deeper layers.
- By detecting the ratios of different isotopes of the same element in the fossil material.
State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help an example. (CBSE 2012)
Inherited traits are the characteristics transmitted from parents to their offspring. Acquired traits are characteristics which are developed during the lifetime of an individual. Acquired traits are not passed on to the next generation. For example, if we breed a group of mice, all their progeny will have tails.
Now, if the tails of these mice are removed by surgery and allowed to breed, the next generation mice will also have tails. If these tails are also removed and allowed to breed, the progeny of mice will again have tails. Removal of tail by surgery is an acquired trait and do not change the genes of germ cells and hence, are not passed on to the next generation.
“An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same. (CBSE 2012)
Experience achieved during the lifetime of an individual does not make any change in the gene of the individual.
For example, if a person reads a book on birds, the knowledge he earns by reading the book does not make any change in the gene, hence, this knowledge will not get automatically transmitted to his next generation. Such a trait is called acquired trait.
“We cannot pass on to our progeny the expences and qualifications earned during our life time”. Justify the statement giving reason and examples. (Delhi 2015)
Acquiring knowledge/skill in one’s lifetime such as dance, music, physical fitness or any other suitable example.
- Such characters/experiences acquired during one’s lifetime do not bring any change in the DNA of the reproducing cell/germ cell.
- Only germ cells are responsible for passing on the characters from the parents to the progeny.
“It is possible that a trait is inherited but may not be expressed.” Give a suitable example to justify this statement. (Foreign 2015)
Yes, it is possible.
Example: When pure tall pea plants are crossed with pure dwarf pea plants, only tall pea plants are obtained in F1 generation.
On selfing tall plants of F1, both tall and dwarf plants are obtained in F2 generation in the ratio 3:1.
Reappearance of the dwarf character, a recessive trait in F2 generation shows that the dwarf trait/character was present in individuals of F2 but it did not express due to the present of tallness, a dominant trait/character.
Explain with an example for each, how the following provides evidences in favour of evolution in organisms : (AI 2015)
(a) Homologous organs
(b) Analogous organs
Homologous organs: Study of homologous organs suggests that the organs having . same structure but performing different functions have evolved from a common ancestor.
Example: forelimbs of a frog, lizard, bird and man.
Analogous organs: These organs show adoption of organs for common use.
Example: wings of butterfly and wings of bat.
Fossils: Fossils provide the missing links between two specises.
Example: Archeopteryx/fossils of some dinosaurs with feathers.
Explain the following: (AI 2015)
(b) Natural Selection
Speciation: It is the process of evolution of a new species from pre-existing species. Occurring due to accumulation of variations. The processes like genetic drift/geographical barriers like mountains, rivers etc., lead to incapability to reproduce amongst themselves in the population.
Natural selection: Change in frequency of some genes in a population gives survival advantage to a species from elimination.
Example: In a population of beetles, a new variation (green colour) gets survival benefit / advantage to green beetles whereas other (red) perishes.
In one of his experiments with pea plants Mendel observed that when a pure tall pea plant is crossed with a pure dwarf pea plant, in the first generation, F1 only tall plants appear. (Delhi 2016)
(a) What happens to the traits of the dwarf plants in this case?
(b) When the F1 generation plants were self-fertilised, he observed that in the plants of second generation, F2 both tall plants and dwarf plants were present. Why did it happen? Explain briefly.
(a) The dwarf traits of the plants is not expressed in the presence of the dominant tall trait.
(b) In the F2 generation, both the tall and dwarf traits are present in the ratio of 3 : 1. This showed that the traits for tallness and dwarfness are present in the F1 generation, but the dwarfness, being the recessive trait does not express itself in the presence of tallness, the dominant trait.
List three distinguishing features, in tabular form, between acquired traits and the inherited traits. (Delhi 2016)
- Do not bring changes in the DNA of germ cells.
- Cannot direct evolution.
- Cannot be passed on to the progeny.
- Bring changes in the DNA of germ cells.
- Can direct evolution
- Can be passed on to the progeny.
Why evolution should not be equated with progress?
Evolution cannot be equated with progress because it seems to have just given rise to more complex body designs. For example bacteria still flourish in spite of a very simple body design while dinosaurs did not survive in spite of complex design. Thus evolution is simply the generation of diversity and shaping of diversity by environmental selection.
List two differences in tabular form between dominant trait and recessive traits. What percentage/proportion of the plants in the F2 generation/progeny were round, in Mendel’s cross between round and wrinkled pea plants? (Foreign 2016)
- The trait which appears in the F1 progeny, is dominant.
- It appears in more numbers.
- The trait which remains hidden or which does not appear in the F1 progeny is the recessive trait.
- It appears in less number.
75% of the plants were with round seeds.
List three factors that provide evidences in favour of evolution in organisms and state the role of each in brief. (Foreign 2016)
Three factors / evidences and their roles:
- Analogous organs: Organisms with similar looking organs may have different origin.
- Homologous organs: Organisms with apparently different looking organs may have similar origin.
- Fossils: Fossils allow us to make estimates of how far back evolutionary relationships go. Fossils when chronologically arranged help in tracing the evolutionary history of an organism.
How do Mendel’s experiment show that traits are inherited independently? (AI 2016)
When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F1 progeny plants are all tall with round seeds: this indicates that tallness and round seeds are the dominant traits. When the F1 plants are self pollinated the F2 progeny consisted of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits.
There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds. Thus it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently.
“Two areas of study namely ‘evolution’ and ‘classification’ are interlinked.” Justify this statement. (AI 2016)
Different forms of organisms/life have evolved during the course of evolution, and classification deals with grouping of these organisms into groups and subgroups based on their similarities and differences.
The more characteristics any two species have in common, the more closely they are related and will have a more recent ancestor (and vice versa).
Thus classification helps tracing the evolutionary relationships between the two organisms hence classification and evolution are interlinked.
Heredity and Evolution Class 10 Important Questions Long Answer Type
Explain the analogous organs and homologous organs. Identify the analogous and homologous organ amongst the following:
Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of human. (CBSE 2007)
Analogous organs are those organs that have same function but have different structural design and origin. E.g., wings of birds and insects.
Homologous organs are those organs in different plants or animals which have the same basic structural design and organ but have different appearance and functions.
Analogous – Wings of an insect, wings of a bat
Homologous – Forelimbs of frog, forelimbs of human and wings of bat.
What is speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species? Explain. (Foreign 2015)
Speciation: Formation of new species from pre-existing ones.
- Natural selection
- Genetic drift
- Geographical Isolation
Geographical isolation cannot be a major factor in the speciation of a self pollinating plant species.
Reason: Physical barrier cannot be created in self pollinating plants.
How do Mendel’s experiments show that the
(a) traits may be dominant or recessive,
(b) traits are inherited independently. (AI 2015)
(a) When Mendel crossed pollinated pure tall pea plants with pure dwarf pea plants, only tall plants were obtained in F1 generation. On self pollinating the F1 progeny, both tall and dwarf plants appeared in F2 generation in the ratio 3:1. Appearance of tall character in both the F1 and F2 shows that it is a dominant character. The absence of dwarf character in F1 generation and its reappearance in F2 shows dwarfness is the recessive character.
(b) When Mendel conducted a dihybrid cross having two sets of characters, he obtained only one set of parental characters in F1 generation whereas in F2 generation he obtained both the set of parental characters now recombined in the ratio of 9:3:3:1. The appearance of new recombinants in the F2 generation along with parental type shows that traits are inherited independently.
What is meant by speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Give reason to justify your answer. (Delhi 2016)
Speciation: The process of formation of a new species from a pre-existing one.
- Genetic drift.
- Mutation / Drastic change in the genes or DNA.
- Natural selection.
- Geographical isolation. (Geographical isolation cannot be a major factor in the speciation of a self-pollinating plant species.)
Reason: Physical barrier cannot be created in self-pollinating plants.
Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution. (AI 2016)
Evolution: The gradual unfolding of organisms occurs from pre-existing organisms through change since the origin of life. It occurs because there is an inbuilt tendency to variation during reproduction due to errors in DNA copying and as a result of sexual reproduction.
It is observed that although fossils appear different from the existing species, they may show certain features similar to the existing species thus providing linkages between pre-existing and existing forms and provide information about the extinct species which were different from the existing species.