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Is this information enough to tell you which of the traits � blood group A or O � is dominant? Why or why not? Answer: This information is not enough. This is because each individual is carrying two alleles. The recessive trait can occur only when who alleles are similar. It blood group A is dominant and O is recessive, then daughter can have blood group O only when both recessive alleles occur together in mother, and father has one allele of O and other of A.
Question 4. How is the sex of the child determined in human beings? All the female gametes carry only X chromosomes. When a sperm fertilizes an egg, the following situations become possible.
Thus there are 50 � 50 chances of a male or female child and none of the parents may Sex determination in humans be considered responsible for it. The sex-determination mechanism is shown alongside. What are the different ways in which individuals with a particular trait may increase in a population?
Answer: Different ways in which individuals with a particular trait may increase in a population are as follow :. Why are traits acquired during the life-time of an individual not inherited? Answer: The traits acquired during the life-time are changes in the non-reproductive cells of the organisms and are not capable of being passed on to the next generation.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics? Answer: The small numbers of surviving tigers are a cause of worry from the point of view of genetics because in tigers there are negligible genetic variations. Due to this they are not well adapted.
The rapid environmental changes cannot be favouable for them. If these changes are not controlled, tigers would be wiped out. What factors would lead to the rise of a new species? Answer: The factors that would lead to the rise of a new species are the following :. Will geographical isolation be a major factor in the speciation of a self- pollinating plant species? Answer: The geographical isolation cannot be major factor in the speciation of a self-pollinating plant species because it does not have to look the plants for its process of reproduction to be carried out.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Answer: Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out reproduction.
Give an example of characteristics being used to determine how close two species are in evolutionary terms. Answer: If similar characteristics are shown in different organisms, then these are considered to be inherited from the common ancestry. It also shows the closeness of the species. For example, bats and birds have some similarity in their wings, so they are closely related, while lizard and squirrel do not have wings so these are not closely related to the birds and bats.
Can the wing of a butterfly and the wing of a bat be considered homologous organs? Answer: The wings of a butterfly and the wings of a bat cannot be considered to be homologous organs because they have different basic designs though they are used for the same purpose of flying.
They are analogous organs. What are fossils? What do they tell us about the process of evolution? Answer: Fossils : Fossils are the remains or traces of a dead organism. These are formed through the formation of sedimentary rocks. They provide following information on the process of evolution. 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: This is because although genetic make up of humans may be slightly different in different races of people, there is no reproductive isolation. Reproductive isolation differentiates one species from the other. Human beings different in size, colour and looks can marry among themselves and produce fertile offspring. Answer: Bacteria is a primitive organism as they came into being very early in evolution. But these organisms are still surviving in the present conditions after millions of years.
This is because they have adapted well to the changing environment over these years. Same is the case for all other organisms like spiders, fishes and chimpanzees which have adapted to their environment and have survived.
Therefore, all the organisms which exist have a body design which is better as it is suited to their environment. 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. In evolutionary terms, we have more in common with : a a Chinese school-boy b a chimpanzee c a spider d a bacterium Answer: a A Chinese school-boy. 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? Answer: This information is not complete. On the basis of this, it cannot be decided light colour trait is dominant or recessive. So it cannot be said until one does not know the nature of this trait in the parents. Question 5. How are the areas of study-evolution and classification interlinked? Justify this statement. Resemblances in organisms are because they have arisen from a common ancestor and differences in them are due to adaptations to different types of environment.
Since the organisms can be graded in order of increasing complexity it indicates at the concept of evolution. Question 6. Explain the terms analogous and homologous organs with examples. For example, The wings of an insect and a bird are analogous organs. Homologous organs : Those organs which have the same basic structure or same basic design but different functions are called homologous organs.
For example, The wing of a bat, flipper of a seal, front leg of a horse and arm of a man are homologous organs. Question 7.
Outline a project which aims to find the dominant coat colour in dogs. Answer: Suppose a black homozygous male is mated with a white homozygous female.
If the progeny has all black dogs then the dominant coat colour is black. Question 8. Explain the importance of fossils in deciding evolutionary relationships. Answer: Fossils play important role in providing evolutionary evidences because by knowning the age of fossils we can know about the evolution process of an organism. For example, a fossil bird called archaeopteryx that looked like a bird had many other features of reptiles. It had feathered wings like those of birds, but teeth and tail like those of reptiles.
Archaeopteryx is, therefore, a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles. Question 9. What evidence do we have for the origin of life from inanimate matter? Haldane at first in suggested that life is originated from inanimate matter. According to him life must have developed from the simple inorganic molecules which were present at that time.
Later, Miller and Urey in presented its evidences. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide, etc. At the end of one week, it was found that about 15 per cent of carbon from methane had been converted into simple compounds and amino acids which make up protein molecules formed in living organisms. This experiment provides the evidence that the life originated from inanimate matter or lifeless matter like inorganic molecules.
Question 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? These variations are inherited and increase the chances of survival of an organism. How is the equal genetic contribution of male and female parents ensured in the progeny? Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete.
When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Answer: Yes, variations that confer an advantage to an individual organism are inherited.
The organism can survive longer in an environment and maintain its existence in the population. Formulae Handbook for Class 10 Maths and Science. Answer: Natural selection selects the individuals having useful variations which ensure their survival in the prevailing conditions of environment. Variant individuals that can withstand or cope with prevailing environment will survive better and will increase in number through differential reproduction.
Answer: Mendel took pea plants with contrasting characteristics � tall plant and dwarf short plant. On cross pollination, he got all tall plants in F1 generation. Then by self pollination of F1 tall plants, he produced second generation F2 consisting of tall and short plants in the ratio of 3 : 1.
Answer: In a dihybrid cross made by Mendel, it was observed that when two pairs of traits or characters were considered; each trait expressed independent of the other.
Thus, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits. A man with blood group A marries a woman with blood 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? Answer: No. This is because we do not know about the blood group of all the progeny. Hence, the information is incomplete to draw any such conclusion.
Answer: The females carry two X-chromosomes. Males have one X and one Y- chromosome. Thus, female is homogametic and male is heterogametic. When a sperm carrying X- chromosome fertilises an egg, the zygote develops into female XX condition. When sperm carrying Y-chromosome fertilises an egg, the zygote develops into a male XY condition.
Thus, sex is determined at the time of fertilisation. Answer: Different ways are : variation, natural selection and genetic drift isolation. Why are traits acquired during the lifetime of an individual not inherited? Answer: Because acquired characters bring changes only in non-reproductive tissues and cannot change the genes of the germ cells.
Thus, acquired traits cannot be passed to next generation. Answer: i If any natural calamity occurs and kills these small number of surviving tigers, they can become extinct resulting in the loss of some genes forever. These both are very important for giving better survival chances to the species. What factors could lead to the rise of a new species? Answer: Genetic variations, natural selection and reproductive isolation could lead to the rise of a new species.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Answer: No, because pollination occurs on the same plant in self-pollinating plant species. Answer: No, because asexual reproduction involves single parent or organism. Give an example of characteristics being used to determine how close two species am in evolutionary terms?
Answer: Homologous organs, analogous organs and vestigial organs help to identify evolutionary relationships amongst the species. Can the wing of butterfly and the wing of a bat be considered homologous organs? Answer: No, wing of a bat and wing of a bird cannot be considered as homologous organs because they have different basic structure.
Answer: Fossils are the impression or remains of ancient life found preserved in the sedimentary rocks. Fossils are direct evidences of evolution. Fossils also help to identify evolutionary relationship between apparently different species. They also tell about the extent of evolution that has taken place.
Page Question 1. Answer: They look different because of interaction of genes with environment which results in change in their appearance. But they belong to the same species as they have same number of chromosomes and can breed among themselves. Answer: No, because different designs are the product of evolution and different species have different body design to suit or adapt to their environment.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing whfte flowers. The progeny all bore violet flowers, but almost half of them are short. An example of homologous organs is a our arm and a dogs fore-leg. Answer: d Both organs in all options have same basic structural design but have different functions and appearance. In evolutionary terms, we have more in common with a a Chinese school-boy.
Answer: a A Chinese school-bpy is also a human being. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. Answer: We can say that light eye colour trait is dominant because only dominant traits are expressed in the first generation. How are the areas of study � evolution and classification� inteilinked?
Answer: Evolution and classification are interlinked with each other in many ways. Genetic drift can lead to accumulation of changes in the generations. Natural selection: According to Darwin, natural selection also plays an important role in bringing about evolution of new species of plants and animals.
According to him variations existed between the individuals of a population and some natural phenomena eliminated those individuals which were less adapted. The surviving population would pass the hereditary advantageous features to their offsprings. With time this process would give rise to organisms different from the original population and new species are formed.
Isolation: When a population of a species splits into two, it cannot reproduce with each other and forms a new species, for example; when a population of beetles feed on bushes on a mountain range, some may start feeding on nearby bushes finding entry into a new subpopulation.
They reproduce with them so genes enter in a new population. Ultimately the two groups will be incapable of reproducing with each other and new species will be formed. Evolution and Classification: The organisms show certain features, like appearance and behaviour which are called characteristics for example; Plants can perform photosynthesis. The basic characteristics are shared by a large number of organisms. More characteristics which two species have in common more closely are related, if they are more closely related then they have common ancestors explain the example of brother sister and cousins.
Evolutionary relationships can be traced with the help of the following :. Homologous organs: Those organs which have the same basic structural design and developmental origin but perform different functions and appearance, for example; Forelimbs of frog, lizard, bird, bat and human beings.
They have same design of bones but they perform different functions. Analogous organs: Those organs which have different basic design and developmental origin but have similar appearance and perform a similar function, for example; wings of bat and bird. Wings of bat are folds of skin attached between fingers. But wing of birds are modified forelimbs. Study of Fossils: Fossils are preserved remains of living organisms that lived in the past.
When living organisms die their bodies decompose but some parts of their body may be in such an environment that they do not decompose for example; if a dead insect gets caught in hot mud it will not decompose quickly but the mud will harden and retain impressions of the body parts of the insects. These impressions are also called fossils: The age of fossil can be estimated in two ways : The fossils that occur closer to earth surface are more recent to those found in deeper layers.
The second method is isotope dating i. Significance of fossils: Fossils are formed layer by layer in the earths crust. The animals and plants which existed earlier are buried in the deeper layer which ones found in the upper layer. It is found that, deeper fossils have simpler structure than found than upper layer.
Complete fossil record of animals like horse, camel, man has helped us to study the stages of evolution. Evolution by stages: Evolution is a continuous and gradual process, complicated organs did not evolve by a single DNA change but were formed by bit by bit change over generations for example; complex organs like eyes were created by bit by bit changes, in between the rudimentary eye in some insects also provided a fitness advantage.
The structure of eye in all organisms is different enough to have evolutionary origins. Some organs even developed for one particular function but later become useful for quite a different function, e. Some dinosaurs had feathers although they could not fly, this shows that birds are closely related to reptiles, since dinosaurs were reptiles Some dissimilar looking structures also evolved from common ancestors.
The current example of such a process is wild cabbage plant from which different vegetables are generated by artificial selection rather than natural selection.
Evolution versus Progress: Evolution can not be called progress from lower forms to higher forms. It is basically forming more complex designs while the simpler once also keep growing. Evolution is generation of diversity with the help of environmental selection. Bacteria which were formed first have the capacity to live in diverse conditions and are still flourishing; on the other hand human beings which are highly evolved species can not be called the pinnacle of evolution but yet another species in the evolving life forms.
Human Evolution: Human evolution has been studied with the help of excavation; time dating and fossil study All human beings belong to single species i. Homo sapiens. Human species have come from Africa. Some of our ancestors left Africa while others stayed on. These migrants slowly spread across the planet i.
They had come into being as an accident of evolution. Although there is a great diversity of human forms all over the world get all humans are single species. Genetics: Branch of science that deals with heredity and variation.
Mendel and his work on Inheritance. Gregor Johann Mendel started his experiments on plant breeding and hybridisation. Mendel was known as Father of Genetics. The plant selected by Mendel was Pisutn sativum garden pea. Mendel used a number of contrasting characters for garden pea. Sex Determination: Phenomenon of decision or determination of sex of an offspring. Sex Chromosomes: In human beings, there are 23 pairs of chromosomes.
Out of these 22 chromosome pairs are called autosomes and the last pair of chromosomes that help in deciding the gender of that individual are called sex chromosome. XX � female; XY � male The cross done shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.
Microevolution: It is the evolution which takes place on a small scale. Example, change in body colour of beetles. Speciation: It is the process of formation of new species. A species is a group of similar individuals that belong to a population that can interbreed and produce fertile offspring.
Speciation takes place when the variation is combined with geographical isolation. Gene flow: It is the exchange of genetic material by interbreeding between populations of the same species or individuals.
Gene flow occurs between populations that are partly but not completely separated. Genetic Drift: It is the random change in the frequency of alleles gene pair in a population over successive generations. Genetic drift takes place due to:. Natural Selection: The process by which nature selects and consolidates those organisms which are more suitably adapted and possesses favourable variations. Artificial Selection: Humans have been a powerful agent in modifying wild species to suit their own requirement throughout ages by using artificial selection.
Example, wheat many varieties obtained due to artificial selection. Heredity : It refers to the transmission of characters or traits from the parents to their offspring. Heredity is the continuity of features from one generation to another which are present in fertilised egg or zygote. The zygote develops into an organism of a particular type only. Genetics : It is the branch of biology which deals with heredity and variation. Genetics is to help our understanding of heredity by knowing how offspring inherit characteristics from their parents.
Variation : It means the differences in the characters or traits among the individuals of a species. Variations occur during reproduction both because of error in DNA copying and as a result of sexual reproduction. Variations contribute to evolution. Causes of variations:. Variations are produced both in sexual and asexual reproduction but amount of variations produced in asexual reproduction are subtle so little that they are hardly noticeable as compared to variations caused due to sexual reproduction.
Genotype : The genetic constitution of an organism e. Phenotype : The appearance of the organism, i. Phenotype is the result of interaction of genes with the environment. Now if genotype is RR phenotype will be red only but if genotype is Rr then also phenotype will be red since R is a dominant gene. Gene : It is the basic unit of inheritance by which characters are transferred from parents to their offspring. Gene consists of a specific length of DNA on a chromosome.
A specific Segment of DNA that provides the information for one protein is called gene for that protein. According to Mendel, both parents must contribute equally to the DNA of the progeny during sexual reproduction.
As both parents determine the trait in the progeny, so both parents must be contributing a copy of the same gene. Chromosomes : These are the long threads present in the nucleus of every cell. Chromosomes are made- up of DNA and protein. Each chromosome contains very long molecule of DNA.
Each gene set is present as separate independent pieces each called a chromosome. Each cell have two copies of each chromosome, one each from male and female parents.
Every germ cell will take one chromosome from each pair and these may be of either maternal or paternal origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species. Such mechanism of inheritance is used by all sexually and asexually reproducing organisms. Allele: It is an alternative form of a gene occupying the same position on a chromosome and affecting the same characters but in two alternative ways, e.
Expressing allele of a gene :. Dominant allele: An allele that affects the phenotype of an organism both in heterozygous and homozygous condition. It is denoted by a capital letter, e. Recessive allele: An allele that affects the phenotype of the organism in absence of a dominant allele, i.
It is denoted by a small alphabet, e. Heterozygous : When both alleles of a particular gene are different, e. Diploid : Cells or organism containing two sets of genes, e. Diploid cells have genetic constitution of 2n. Haploid : Cells or organism containing one set of genes, e.
Haploid cells have genetic constitution of n. Monohybrid cross : A cross between two parents taking the alternative traits of one single character, e.
Monohybrid Ratio :. Dihybrid cross: A cross between two parents taking into consideration alternative traits of two different characters, e. Dihybrid Ratio :. The genes I A and I B show no dominance over each other they are codominant, i. But these both genes are dominant over the gene I O.
Therefore, blood group of a person depends on the type of genes present, e. Homologous chromosomes: A pair of corresponding chromosomes of the same shape and size, one from each parent. Autosomes and Sex chromosomes : The identical � chromosome pairs are called autosomes. The chromosome pair which is different are called sex chromosomes. Humans have 23 pairs of chromosomes. Molecular Phylogeny: It is the study of evolutionary relationships by comparing DNA of different species.
Natural selection : Natural selection is one of the basic mechanisms of evolution, along with mutation, migration and genetic drift. Natural selection means the environmental conditions prevailing around an organism against which organism adapts itself, grows � and reproduces further. This leads to a change in the composition of genes within a population further causing evolution.
Thus, it can be said that, Natural selection results in adaptation in population to fit their environment better. Thus, natural selection direct evolution in the population of a particular species. Fossils of the information which they provide regarding evolution: Fossils are the remains of ancient life forms, which got preserved somehow in the layers of earth, snow or oil.
Information given by fossils:. Genetic drift: The change in the frequency of some genes in a population which provides diversity without any survival advantage is called genetic drift. The various ways in which individuals with a particular trait may increase in a population : Differences in population are responsible for the diversity such as, colour of eyes, hair, shape of ear lobes.
Evidence of evolution: Errors in DNA copying mutation and sexual reproduction lead to variations which form the basis of evolution. Characteristics that are common in different kinds of living organisms provide evidence in favour of evolution. Evolution : Evolution can be defined as a naturally occurring slow, continuous and irreversible process of change.
The gradual change of living organisms from pre-existing organisms since the beginning of life is called organic evolution. Whereas, gradual change in elements from one form to another with time is termed as inorganic evolution, i. Inherited traits : are those traits which are passed from one generation to another through specific genes.
Any change in DNA of the germ cells will be passed. Acquired traits : are those traits which are acquired by the organism in its lifetime, e. Speciation : It means the origin of new species from the existing ones. It happens when different populations of the same species evolve along different lines. How speciation occurs? Complex organs like eye has evolved from rudimentary organs, e.
A change that is useful for one property to start with can become useful later for quite a different function e. But later, they might be useful for flight.
Some heavy birds and reptiles also have feathers but they do not fly. Some very dissimilar looking structures evolve from a common ancestral design, e.
It suggests that, if these selections were not done then there would have been only wild cabbage. Homologous organs are organs having same origin and basic structure but they appear different and perform different functions in various organisms, e.
Similarities in basic structure of homologous organs in different organisms, indifferent groups indicate common ancestry. Analogous organs are organs, which look similar because they perform same function, but they do not have same origin and basic structure. DNA is a chemical in the chromosome which carries the traits in a coded form. Gene is the part of a chromosome which controls a specific biological function. He concluded that traits are independently inherited Conclusion Round and yellow seeds Round and green seeds Wrinkled and yellow seeds Wrinkled and green seeds Different species use different strategies for this : In some animals the temperature at which fertilized eggs are kept determines whether the developing animals will be males or females.
Some animals like snails can change sex indicating that sex is not genetically determined.
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