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Hindi Question English Question Answers Marks Category Manage
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If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
In asexual reproduction, the resulting offspring are identical to the parents (have a near exact copy of their parents DNA). However, sometimes this copying of DNA is not accurate, so the newly formed DNA has some variations giving rise to a new trait. This trait is then inherited by future generations and successive generations keep accumulating variations. Therefore, if a trait A exists in 10% of the population and a trait B exists in 60% of the same population, we can conclude that traint B has arisen earlier because the trait has been replicating and existing in a higher percentage of the population.
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How does the creation of variations in a species promote survival?
Species are adapted to survive in a particular habitat. Drastic changes in the environment can disturb the habitat and prove fatal for certain species. For example, there are many microorganisms that inhabit freshwater ponds. If there is a sudden increase in the temperature of water, it will kill the bacteria living in it. However, some species of bacteria that are resistant to heat shall survive in the heat. These species will survive and reproduce in the changed environment. If there were no heat-resistant variants, the entire species of bacteria would be extinct. Thus, creation of variations in a species promotes its survival.
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How do Mendel’s experiments show that traits may be dominant or recessive?
Mendel conducted experiments on pea plants with a single character ((with two alternative traits) called monohybrid cross. He crossed true breeding tall plants (TT) with true breeding dwarf plants. In the first filial generation he received only tall plants. The dwarf trait did not appear in the F1 generation. Self-pollination of the F1 progeny resulted in both tall and dwarf plants. On the basis of the monohybrid crosses, Mendel conc luded that out of the two traits of a character, one is dominant and the other is recessive. The dominant trait always expresses itself while the expression of the recessive trait is masked in the presence of the dominant trait. recessive trait. The recessive trait is expressed only in homozygous condition. Also, the tall plants in F1 were not true breeding. They were heterozygous (Tt) tall plants. The dominant allele (T) suppressed the expression of the recessive allele (t). Self-pollination in F1 generation resulted in F2 generation that showed a variety of seeds. F2 progeny was found to have yellow round seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1. The F2 generation had two new variants of seeds - round green and yellow wrinkled (different from the parental types). From this, we can conclude that the genes for the two characters are assorted independently.
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What are the different ways in which individuals with a particular trait may increase in a population?
The different ways in which individuals with a particular trait may increase in a population are: • Natural selection - Certain variations give survival advantage to individuals in a population in a changed environment resulting in an increase in their population. • Genetic drift: Accidents in small populations, even if they give no survival advantage also leads to an increase of certain individuals in a population. • Some traits are not inherited but acquired by an individual during its lifetime. The acquired characters help the individual to survive better and increase its population.
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Why are traits acquired during the life-time of an individual not inherited?
In reproduction, parents pass on the germ cells to the progeny. So, any changes in the germ cells (leading to variation or new traits) are inherited by the progeny. Some traits are acquired by an individual during its lifetime due to environmental influences or other external factors. An acquired trait involves change in non- reproductive tissues (somatic cells). Since acquired traits do not involve any change in the germ cells, therefore, these traits cannot be inherited.
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Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
A small population of any species will accumulate very less variations. When such a species reproduces, there are less chances of having progeny with some useful variations (that will give better survival advantage). So, in the case of a disease they will not be able to survive. They will become extinct and the genes will be lost forever.
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What factors could lead to the rise of a new species?
Speciation is the evolutionary process by which reproductively isolated biological populations evolve to become distinct species. Factors which could lead to the formation of new species are: (i) Genetic drift (ii) Natural selection (iii) Severe DNA change. (iv) A variation may occur which does not allow sexual act between two groups (Reproductive isolation).
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Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not
Geographical isolation prevents transfer of genes between two species. In self-pollinating plant, pollen is transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant. It does not require any external agent for pollination, neither is it dependant on another plant for pollination. So, geographical isolation cannot affect the speciation of a self-pollinating plant.
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Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Geographical isolation prevents transfer of genes (gene flow) between populations of a species. In asexual reproduction a single oragnism is capable of giving rise to a new individual. In these reproducing organisms, variations can occur only when there is an error during the copying of DNA. Therefore, geographical isolation cannot affect the formation of new species in an asexually reproducing organism.
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Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Similarities in characteristics help us to trace evolutionary relationships between organisms. Some characteristics in different organisms are similar because they are inherited from a common ancestor. And these provide a link between different stages of evolution of species. Feathers that we see on birds today were also present on dinosaurs. However, dinosaurs did not use these feathers to fly but as an insulation. Birds seem to have later adapted the feathers for flight. This, indicates that birds are very closely related to reptiles, since dinosaurs were reptiles. This also proves that reptiles and birds are closely related and that the evolution of wings started in reptiles
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Can the wing of a butterfly and the wing of a bat be considered as homologous organs?
The organs which have the same fundamental structure but are different in function are called homologous organs. The wings of a butterfly and the wings of a bat are not homologous organs as they do not have the same origin or the same basic structure. The wings of a butterfly and wings of a bat are analogous organs as they perform the same function of flight even though their origin and structure is different.
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What are fossils? What do they tell us about the process of evolution?
Fossils are remains or imprints of hard parts of the animals such as skeletal structures that once inhabited earth. Fossils provide one of the most acceptable evidence in support of evolution, because we can study evolutionary past of organisms in the form of their fossils. By studying the fossils we can identify the changes that have occurred in these organisms to give rise to the present-day forms. They act as a connecting link between the organisms of the past and the organisms of the present.
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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?
A species is a group of interbreeding individuals. Skin colour, looks, and size are all the observable features of human beings which are generally environmentally controlled. Various human races are formed based on these features. However, all human beings irrespective of skin colour, height, language, race etc are capable of reproducing with each other and producing offspring. Therefore, all human beings belong to a single species Homo sapiens.
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In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
In evolutionary terms, we cannot say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design. Evolutionary process takes into account the development of most efficient and suitable features in a body design for survival and adaptation favoring a particular niche. For example, organisms with a complex body design may not survive in particular situation whereas, bacteria with the simplest body design is able to survive in extreme habitats. Evolution only leads to development of complex body designs and cannot be equated with progress.
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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 make-up of the tall parent can be depicted as (a) TTWW (b) TTww (c) TtWW (d) TtWw
(c) There are two flower colours violet and white but F1 showed only violet flowers. This means violet flower colour (V) is the dominant trait that masks the recessive trait (v) (white flower colour). The F1 had half tall and half short plants. This indicates both dominant and recessive traits expressed in the F1 progeny. So, we can infer that the tall plants were not true breeding and must be genetically heterozygous for the character height (Tt). So, the genetic make-up of the tall parent can be depicted as TtVV. Therefore, the cross involved in the given question. Therefore, half the progeny is tall, but all of them have violet flowers.
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An example of homologous organs is (a) our arm and a dog’s fore-leg. (b) our teeth and an elephant’s tusks. (c) potato and runners of grass. (d) all of the above.
(d) All of the Above. As in all cases the basic internal structure and origin of the organs are the same though they differ functionally. For example, elephant's tusk is a modified incisor. So, origin is the same but the function is different. Tubers of potato and grass runners are both stem modifications but functions are different, hence these are homologous organs.
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In evolutionary terms, we have more in common with (a) a Chinese school-boy. (b) a chimpanzee. (c) a spider. (d) A bacterium
(a) In evolutionary terms, we have more in common with a Chinese school boy. Because both belong to the same species Homo sapiens. Chimpanzees and humans both have a common ancestor but are two different species.
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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?
Children with light-coloured eyes can either have LL or Ll or ll genotypes. Let us assume that the children have LL (both dominant alleles) genotype. This is possible only when both parents are also of the LL genotype. If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype. Therefore, it cannot be concluded whether light eye colour is dominant or recessive.
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How are the areas of study − evolution and classification − interlinked?
Classification is the process by which scientists group living organisms based on their similarities. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor. For example, in a family, a brother and sister are closely related than their cousins. A brother and sister have a recent common ancestor i.e., their parents. A brother sister and their cousin are also related but less than the sister and her brother. The grandparents are the common ancestor for a brother and sister and their cousin. Due to sexual reproduction, there is an accumulation of variation over generations which leads to creation of different phenotypes and genotypes as we move down a family (evolution) tree.
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Explain the terms analogous and homologous organs with examples.
Homologous organs are similar in origin (or are embryologically similar) but perform different functions. Forelimbs of frog, lizard, pigeon, bats, whales, horses and humans have the same basic structural plan but different functions. For example, the wings help in flight whereas human forearm helps in various activities. Homologous organs The organs which have similar functions but are different in their structural details and origin are called analogous organs. For example, the wings of a bird and a bat are similar in function, but this similarity does not mean that these animals are more closely related. The basic structure of the wings of insects is different from that of a bird and a bat but similar in function. Also, on careful observation we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Similarly, fins of fishes and flippers of whales are also examples of analogous organs. Therefore, these organs are analogous organs.
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Outline a project which aims to find the dominant coat colour in dogs.
Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog. A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, if a dog inherits The “B” gene, it can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb) Since black (B) is dominant, all the offspring are black i.e. phenotype is black. However, genotypically they are heterozygous for the B allele (Bb). That is all offspring are heterozygous black. If the F1 heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) off springs.
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Explain the importance of fossils in deciding evolutionary relationships.
Fossils are the remains of the organism that once existed on earth. They represent the ancestors of the plants and animals that are alive today. Fossils are buried under layers of earth, mud and silt and are preserved for millions of years. Fossils are formed when an animal dies and is buried under the earth. Soft tissues quickly decompose leaving the hard bones or shells behind. Over time sediment builds over the top and hardens into rock. Deeper within the earth, older is the fossil. If we dig into the earth and start finding fossils, the fossils we find closer to the surface are more recent than the fossils we find in deeper layers. Let us start 100 million years ago. Some invertebrates on the sea-bed die, and are buried in the sand. More sand accumulates, and sandstone forms under pressure. Millions of years later, dinosaurs living in the area die, and their bodies, too, are buried in mud. This mud is also compressed into rock, above the rock containing the earlier invertebrate fossils. Then, millions of years later, some horse-like creatures died in that area and got fossilized in rocks above the dinosaur fossils. Again, millions of years later, the bodies of horse-like creatures dying in the area are fossilized in rocks above these earlier rocks. If that area is excavated deeper, then the dinosaur and invertebrates’ fossils can also be found. Thus, by digging that area, scientists can easily predict that horse-like animals evolved later than the dinosaurs and the invertebrates. Thus, the above example suggests that the fossils found closer to the surface of the earth are more recent ones than the fossils present in deeper layers. Layers of fossils
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What evidence do we have for the origin of life from inanimate matter?
Stanley L. Miller and Harold C. Urey conducted an experiment in 1953 to understand the origin of life on the earth. A British scientist, J.B.S. Haldane, suggested that life originated from simple inorganic molecules. He believed that when the earth was formed, it was a hot gaseous mass containing elements such as nitrogen, oxygen, carbon, hydrogen, etc. These elements combined to form molecules like water (H2O), carbon dioxide (CO2), methane (CH4), ammonia (NH3), etc. After the formation of water, slowly the earth surface cooled and the inorganic molecules interacted with one another in water to form simple organic molecules such as sugars, fatty acids, amino acids, etc. The energy for these reactions was provided by solar radiation, lightning, volcanic eruptions, etc. Miller and Urey assembled an atmosphere similar to that thought to exist on early earth (this had molecules like ammonia, methane and hydrogen supplied, but no oxygen) over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases 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.
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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?
In sexual reproduction, two parents are involved. Both parents contribute their genes to the offspring. The child obtains half number of chromosomes from the father and half from the mother i.e. he inherits one copy of genes from father and another copy from the mother. So, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction leads to variations. In asexual reproduction, chance variations can only occur when the copying of DNA is not accurate. Also, during asexual reproduction, the offspring inherits the entire cellular apparatus from the parent. If there are major variations then the resultant DNA will not be able to survive inside the inherited cellular apparatus. However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable. Sexual reproduction helps the organism to adapt better to the environment. Variations help the species to survive in all the conditions. Environmental conditions such as a disease, pests, and food availability can change suddenly affect a place. In this situation, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms. However, in case of a sudden change in the environment of asexually reproducing species can cause their extinction.
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How is the equal genetic contribution of male and female parents ensured in the progeny?
In human beings, each somatic cell of the body contains 23 pairs of chromosomes. Out of the 23 pairs of chromosomes, 22 pairs are known as autosomes and the remaining one pair is called sex chromosomes represented as X and Y. Females have two X chromosomes and males have one X and one Y chromosome. During gametogenesis (gamete formation), meiosis occurs and the gametes receive half the number of chromosomes. Therefore, the male gametes have 22 autosomes and either X or Y chromosome. The female gamete, on the other hand, has 22 autosomes and X chromosome. During sexual reproduction, the male and female gametes fuse and the number of chromosomes is again restored in the zygote. The progeny receives 22 autosomes and one X or Y chromosome from male parent and 22 autosomes and one X chromosome from the female parent.
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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?
Natural selection is one of the basic mechanisms of evolution. Natural selection favours variations that offer a survival advantage. Individuals with survival davantage reproduce within the population and pass on the favourable variation to the progeny. Evolution of organisms occurs as a result of this natural selection. However, there can be some other variations that occur by chance (arise only accidentally) and do not offer any survival advantage. If such variations occur in small populations, they can change the frequency of some genes in the population even if they are not important for survival. This accidental change in the frequency of genes in small populations is referred to as genetic drift. So, both types of variations can survive in a population.
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