GENE: A unit of DNA or a segment of DNA which controls specific characteristic of an organism.

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1 In asexual reproduction, all the off springs are exactly identical to one another as well as to parents because of same genetic makeup. In sexual reproduction the various off springs are similar to their parents but are not identical to items or to one another because of genetic various except IDENTICAL TWINS. Identical Twins: grow from a single cell which splits after fertilization. Look alike Non Identical twins: Look less like they grow from 2 different fertilized cells & hence don t have exactly same genetic material. Heredity: The transmission of characters (traits) from the parents to their off springs is called Heredity. Variation: The differences in the characters among the individuals of a species are called variation is necessity for organic evolution. Both Heredity & variation are fundamental factors in the process of Evolution of an organism. Genetics: The branch of biology which studies heredity & variation is called genetic. Terms gene was coined by scientist Johanssen in Chromosomes: Chromosomes are thread like structures present in the nucleus of a cell which contain hereditary information of the cell. They are made up of DNA & proteins. Dipoid Cell: A cell which has the full no. of chromosomes with two of each pair, is called a diploid us. Hiploid Cell: A cell c half the no. of chromosomes with one of each pair e.g. gamete cell/sex cell. Autosomes: All the chromosomes in a cell (except sex chromosomes) are called autosomes. Karyotype: During metaphase stage of cell division, the chromosomes become shorter, thicker & can be seen very clearly. In order to study the no. shape, size and type of chromosomes of an individual, the chromosomes during metaphase, are arranged acc to their length & position of centromere. Such an arrangement of chromosomes for the purpose of studying is called Karyotype. Identifying a chromosome thru microscope, special staming technique called Banding Technique is used. Study of karyotype of an individual helps in the diagnosis of genetically disorders. Down s Syndrome: Any variation in the no. of chromosomes from the normal no or any change in the shape of chromosome during fertilization can lead to severe abnormality or disorder in the child after birth which are called Genetic / Heredity Disorder. e.g.down s syndrome which is caused by inheritance of an extra 21st chromosome. In this syndrome, full mental development does not take place. Symptoms: Mental retardation, Flattened, nose, Defective ears, widely separated eyes, short & broad neck, protruding tongue, small & sturdy hands widely. Gene: Gene is the unit of inheritance. Various genes are located in the chromosomes at fixed position genes are responsible for our characteristic features.chemically gene is a segment of a large polynucleotide molecule called de oxyribonucleic acid DNA: Dexyribo nucleic acid DNA was first isolated by Frederick meisher from the nucleus of the pus cells. It is acidic in nature so the name is nucleic acid. DNA is a macromolecule/polymer which is made up of a large no. of smaller units called Nucleotide. So DNA is a polynucleotide. Nucleotide is the basic structure unit of DNA. GENETICS: The study of heredity and variation. HEREDITY: The transmission of characters (or traits) from the parents to their offspring. VARIATION: The differences in the characters among the individuals of a species. CHROMOSOME: A thread like structure in the nucleus of cell formed of DNA and protein which carries the genes. GENE: A unit of DNA or a segment of DNA which controls specific characteristic of an organism.

2 ALLELES: They are various forms of a gene which occur at the same particular position or locus over the chromosomes. DOMINANT GENE: The gene which decide the expression of a character even in the presence of an alternative gene. RECESSIVE GENE: The gene which decides the expression of an organism in the presence of another identical gene. GENOTYPE: It is the description of genes present in an organism. PHENOTYPE: The characteristic which is visible in an organism. F1 GENERATION: First filial generation when two parents cross to produce progeny (offspring s), then their progeny is called F1 generation. HYBRID: A new form of plant resulting from a cross of different varieties of plants. AUTOSOMES: The chromosomes except those involved in the determination of sex. SEX-CHROMOSOME: The chromosomes which determine the sex of an individual. FOSSILS: The remnants or impressions of organisms that lived in the remote past. EVOLUTION: The sequence of gradual changes which take place in the primitive organisms over millions of years and result in formation of new species PHYLOGENY: Evolutionary history of organism. ONTOGENY: Developmental history of organism. HOMOLOGOUS ORGANS: Organs which have the same basic structure and developmental origin but have different function and appearance. E.g. fore limb of a frog, a bird and a man. ANALOGOUS ORGANS: Organs which have different basic structure and developmental origin but perform similar function. E.g. the wings of an insect and a bird. VESTIGEAL ORGAN: Organs which are functionless and rudimentary in organisms but functional were in the ancestor. E.g. vermiform appendix, nictitating membrane. BIOGENETIC LAW: It states that Ontogeny recapitulates phylogeny. Genetic Drift: Random change in the frequency of genes in a population over successive generations. Heredity:- The passing of traits from the parents to offspring is called heredity. This is heredity which is responsible for many commonly observable facts; like siblings looking similar in overall appearance. Genotype:- The complete set of genes in an organism s genome is called genotype. Phenotype:- The observable characters in an organism make the phenotype. Phenotype is a result of genotype s interaction with the environment. Due to this reason, many phenotypes are not inheritable. Acquired Traits:- Traits; which are acquired due to interaction with the environment; are called acquired traits. Acquired traits are not inheritable. For example; if a boxer develops bulging biceps, it does not mean that his son would be borne with bulging biceps. Inheritable Traits:- Traits; which can be expressed in subsequent generations; are called inheritable traits. Such traits bring a change in the genotype of the organism and hence become inheritable. Accumulation of Variations During Reproduction:- Asexual reproduction involves a single parent and is hence not ideal ideal for facilitating variations. Some minor variations do occur due to inaccuracies in DNA replication. But the quantum of variations would be too little and would take too many years to show effect. Sexual reproduction, on the other hand, is ideal for facilitating variations because two parents are involved in it. The offspring s genotype is contributed by two parents and hence chances of variations are very high. RULES OF INHERITANCE Gregor Johann Mendel conducted experiments on pea plants and proposed the rules of inheritance; based on his observations. Mendel observed that characters are often present in pairs. A pair of contrasting characters is called allele. POSSIBLE REASONS OF PEA PLANTS USED BY MENDEL:

3 Pea can be termed as biennial plant, i.e. two generations of a pea plant can grow in a given year. This means that Mendel could get enough time to observe a larger number of generations. Many easily identifiable and contrasting characters are present in pea plants. Cross pollination can be easily induced in pea plants. Monohybrid Cross: The cross in which just two contrasting characters are studied is called monohybrid cross. Mendel did monohybrid cross for his first experiment. He selected a pair of contrasting characters for that experiment. Let us take the example of cross between tall plants and short plants. The figure; given here shows the results of this experiment. TT represents the genotype of tall plant and tt represents the genotype of short plants. In the F2 generation, all plants were tall but their genotype was Tt; which means they were not pure tall plants. This could be established by the appearance of the character of shortness in the F2 generation; in which most of the plants were tall and some of the plants were short. This experiment showed that the character of shortness of recessive in F1 generation and hence could not be observed. The ratio of number of tall plants to that of short plants in F2 generation was 3 : 1. Mendel s First Law: The Law of Segregation: Every individual possesses a pair of alleles for a particular trait. During gamete formation, a gamete receives only one trait from the alleles. A particular trait can be dominant or recessive in a particular generation. Dihybrid Cross: The cross in which two pairs of characters are studied is called dihybrid cross. In his second experiment, Mendel used dihybrid cross. Let us take example between plants with round and green seeds and those with wrinkled and yellow seeds. The genotype of round and green seeds is shown by RRyy and that of wrinkled and yellow seeds is shown by rryy. In the F1 generation, all plants produced round and yellow seeds; which means that wrinkled texture was the recessive character and so was the green colour of seeds. When plants of F1 generation were allowed to self pollinate; it was observed that most of the plants in F2 generation produced round and yellow seeds. Some plants produces round green seeds, some produced wrinkled yellow seeds and some produced wrinkled green seeds. The ratio was 9 : 3 : 3 : 1; as shown in the figure. Mendel s Second Law: Law of Independent Assortment: Alleles of different characters separate independent from each other during gamete formation. In the above example; alleles of texture were assorted independently from those of seed colour. SEX DETERMINATION IN HUMANS:

4 Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23rd pair is composed of different types of chromosomes which are named as X and Y chromosomes. The 23rd pair contains one X and one Y chromosome in a male. On the other hand, the 23rd pair in a female contains X chromosomes. This means that all the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome as the 23rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote would develop into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child. EVOLUTION The change in inherited traits in biological population over subsequent generations is called evolution. Scientists have proven that life evolved in the form of simple unicellular organisms on this earth; and all the organisms which are present today have evolved from a common ancestor. The idea of evolution is based on the premise of a common ancestry. To understand how evolution takes place, let us take some imaginary examples. SITUATION 1:- A group of red ants is living in a bush. As hunting birds can easily spot red ants in the green background, they enjoy feasting on ants. Because of some error in DNA replication, some blue ants come into origin. Hunting birds cannot spot blue ants against a green background. As a result, blue ants survive and red ants become extinct over a period of time. The origin of blue ants happened by chance but it gave survival benefit to the ants. Finally, blue ants could survive and proliferated in the surrounding. SITUATION 2:- In the same group; some blue ants came into origin. Ants of both colours were almost equal in population. One day, an elephant cam and trampled the bushes. All the red ants perished in the accident; leaving only the blue ants. This resulted in extinction of red ants but blue ants could continue their race. The survival of blue ants was because of an accident and the accident was the cause of natural selection. SITUATION 3:- A group of red ants was living in a bush. Due to draught like conditions, availability of food became a problem for the ants. All the ants became weak and underweight. Subsequent generations comprised of smaller ants and the trend continued for a few generations. Situations changed and plenty of food became available. Ants once again developed to their normal size. In this case, the change in size was a change in

5 phenotype and hence was not inheritable. The change in size could not produce variation and evolution in the species. DARWIN S THEORY OF EVOLUTION: Charles Darwin wrote his famous book Origin of Species. He threw new insights on evolution of species. Some salient points of Darwin s theory are as follows: Organisms have unlimited capacity to reproduce:- Organisms can reproduce offspring at a fast pace. This is necessary for survival, because a higher number of offspring ensures that at least some of them could survive. Each organism has to struggle for its day to day survival. For example; a frog lays thousands of eggs at one go. The spawn is released in water and it is left to fend for itself. Most of the eggs are either washed away or are eaten by predators. However, some portion of eggs from the spawn develops into tadpoles. Once again, many tadpoles are eaten up by predators; leaving a few which develop into adults. It is evident, that a large number of eggs is needed to ensure that at least some of them develop into adults. NATURAL SELECTION:- Different individuals of a particular species have different traits. Those with more suitable traits are selected by the nature. Each organism needs a particular trait for finding food and finding a mate. Those with better traits are finally able to pass on their traits to the next generation. SURVIVAL OF THE FITTEST: Those organisms which are the fittest are able to survive, while others perish. That is how many species become extinct and some species continue to evolve over a period of time. MOLECULAR ORIGIN OF LIFE: Stanley L. Miller and Harold C. Urey, conducted the Miller-Urey experiment in 1953 to demonstrate how the life would have originated on the earth. They created an environment in laboratory which mimicked the environment of earth as it was during the time of origin of life. Water, methane, ammonia and hydrogen were used in that experiment. The liquid was heated to initiate evaporation and electrodes were used to create electric discharge. At the end of two weeks, some organic molecules were formed in the setup. Some amino acids and sugar were also formed. This proved the hypothesis of J. B. S. Haldane that life originated from inorganic raw materials. SPECIATION: The process of origin of a new species is called speciation. A species is a group of organisms in which most of the characters are similar and members of a species are able to breed among themselves. Speciation can happen if two groups of the same species are somehow prevented from interbreeding for several generations. This can happen because of geographical segregation or because of some genetic changes. Evolution of new species, because of geographical segregation is called genetic drift. EVOLUTION AND CLASSIFICATION The modern system of classification is based on evolutionary relationship. Due to this, this is also known as phylogenetic classification. The kingdom is the highest taxa, while the species is the lowest taxa. Members of a species have a higher number of common characters, than members of a kingdom. For example; all human beings belong to the species Homo sapiens. Human beings can interbreed; irrespective of their race or skin colour. All human beings come under the class mammalia; as do the monkeys, elephants and cows. Apparently, each species of the class mammalian is quite different yet they have certain common characters; like hairs on the body and mammary glands in females. Similarly, all animals are eukaryotes and cell wall is absent in their cells. The degree of similarity or dissimilarity shows that all animals have evolved from a common ancestor. Homologous Organs: Organs which have common design but serve different functions in different animals are called homologous organs. For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals. Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools. This shows that frogs, birds and humans have evolved from a common ancestor. Analogous Organs: Organs which have different design but serve a common function in different animals are called analogous organs. Wings of birds and wings of bat are good examples of a pair of analogous organs. Wings of birds are composed of all the bones of forelimb and are covered with feathers. Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure. Yet wings in both the organisms are used for flying. Fossils: The preserved remains of animals or plants or other organisms from the distant past are called fossils. The term distant is a key term in this definition. Scientists usually take 10,000 years as the minimum age for the

6 remains to be categorized as fossil. Many fossils have been discovered till date. These fossils tell us about many extinct animals and also give insights into how the evolution could have taken place. EVOLUTION BY STAGES: Evolution of complex organs and thus of complex organisms has happened in stages. Let us take the example of evolution of eyes. Planaria is the first animal which shows eye like structure. The dark spots on planaria are light sensitive spots but a planaria cannot distinguish between two different objects. Eyes of insects are compound eyes which are made up of thousands of optical surfaces. Eyes of higher animals are simple eyes which are composed of a single lens. Most of the animals cannot differentiate among colours. Depth perception is also weak in many animals. Human eyes are the most advanced; because humans can recognize colours and have very good depth perception. Most of the tetra pods have to use all the four limbs for locomotion. Some apes can walk up to smaller distances by using just the hind limbs. Humans have finally evolved the bipedal walking. EVOLUTION VS PROGRESS: 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 from any angle. Bacteria are known to survive some of the harshest climates; like craters of 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. Colourful feathers of a male peacock are very good when it comes to attract a female. But because of its conspicuous feathers, it can be easily spotted by a predator. Because of its bulky feather it cannot fly away to safety. HUMAN EVOLUTION: The modern humans are called Homo sapiens. Many scientific investigations have shown that the modern humans evolved in Africa. They migrated towards north; in due course of time and settled near what is known as the Mediterranean Sea. When the ice age ended, melting of ice resulted in the in water level. The humans migrated in different directions from that area. One branch went to the western Asia, then to the Indian Peninsula and finally to Australia. From the Indian Peninsula, branch migrated towards China and subsequently to the North America. From North America, the humans migrated to the South America. From the Mediterranean Sea, the second branch migrated towards Europe; where they are believed to replace the Neanderthals. COMPONENTS OF A NUCLEOTIDE: 1. a nitrogen contain base 2. a pentose sugar 3. a phosphate gp Any one of nitrogen base pairs up only c a specific nitrogenous base of the opposite side. Such specific pairing is called COMPLIMENTARY PAIRING. (Adenine) A pairs up c T (Thymine) (Cytosine) C pairs up c G (Guanine) DNA molecule is like that of a spiral staircase in which both the railing of the staircase are made of sugar & phosphate molecules alternative each other and held together by strong chemical bonds whereas the steps of the staircase are made of complimentary nitrogenous bases held together by weak bonds.dna structure established by Wastson & Crick in 1953.Each helical turn of the DNA molecule has a length of 3.4 nm in which 10 nucleotide units are present.

7 Genetic Engineering: The technique for altering an organisms genetic makeup inserting genes from other organism its chromosomes is called Genetic Engineering. Sex Determination: The process by which the sex of a person is determined is called sex determination. The Chromosomes which determine the sex of a person called sex chromosomes which are of 2 types X & Y. XX combination is always found in females XY combination is always found in males. So it is the sperm (carrying either X or Y) which determines the sex of a child ORGANIC EVOLUTION Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of yrs. In which non species are provided. Some import ants sources which provide evidence for organic evolution are Fossils Homologus organs Analogus organs Vestigial organ Embryology Homologus organ: Organs having similar basic structure & origin but different functions e.g. pore nubs of a frog, birds & man. Analogous organs: The organs with different basic structure but have similar appearance & perform similar functions. E.g. wings of an insect & a bird. Vestigial organs: Organs which are functionless useless but were functional in ancestors e.g. Vermiform appendix Nietuting membrane. Embrgology: The study of the development of the embryo of an animal is called Embryology. Biogenetic law: It states that Ontogeny recapitulates Phylogeny It means that during the development of the embryo of any organism, its complete evolutionary history is repeated. THEORIES OF EVOLUTION 1. Lamarckism 2. Darwinism 3. Synthetic Theory of Evolution LAMARCKISM: IT STATES (a) The use & disuse of an organ by an organism leads to acquiring of variation in the features of that organ. (b) These variations (acquired characters) are inherited by the offspring s. (c) This leads to evolution this theory was criticsed by August Weismann who rejected the idea of inheritance of acquired characteristics.

8 DARWINISM / THEORY OF NATURAL SELECTION (a) All the species produce a large no of offspring s but population remains fairly constant due to struggle bt the members of same species & different species for food, space & mate (b) This struggle eliminates the unfit individuals. (Survival of the fittest) (c) This gives origin to variations which pass into progeny & over a long period of time, leads to origin of new species. Limitations: It could not explain how the variations arise. SYNTHETIC THEORY OF EVOLUTION: The most accepted theory these a day s which says that origin of species is based on the interaction of genetic variation & natural selection.

9 POINT TO REMEMBER:- 1. Species maintain continuity by reproduction. 2. Variation in different degrees occurs. 3. Variants have unequal chances of survival. 4. In sexually reproducing individuals, for the same trait genes have two copies. Unidentical copies bear dominant and recessive nature. 5. Traits separately inherited, yields new combinations of traits in progeny. 6. The sex of human progeny is determined by the sex chromosomes inherited from father. 7. Variation in combination with geographical isolation might lead to speciation. 8. Evolutionary relationship among living organisms become visible in hierarchy of classification. 9. Study of living forms as well as dead remains of organisms emerges as evolutionary scene. 10. DNA changes accumulated over a time span has resulted in evolution of complex organs like eye as exhibited by structure of eye in different animals. 11. Features like feathers have evolved as a function of change in allocated task. 12. Evolution is not progress from lower to higher forms. VERY SHORT ANSWER QUESTIONS (1 mark) 1. Who proposed the theory of inheritance of acquired characters? Answer: J.B. Lamarck. 2. State one of the evolutionary forces leading to the origin of a new species according to the synthetic theory of evolution. Answer: Origin of new species is based on natural selection acting on genetic variations that appear among the members of a population. 3. Give an example of a vestigial organ present in human body. Answer: Vermiform appendix. 4. What is the evolutionary significance of the fossil Archaeopteryx? Answer: Archaeopteryx is the connecting link between reptiles and birds. It has both reptilian on features and

10 avian (bird-like) features. 5. Who proposed the double helical model of DNA? Answer: Watson and Crick. 6. Who proposed the theory of natural selection? Answer: Charles Darwin. 7. What is retro virus? Answer: A virus with RNA as the genetic material eg: HIV is a retro virus. 8. What is a genetically modified organism (GMO)? Answer: The organism that contains a segment of foreign DNA. 9. Name any two genetic diseases. Answer: Hemophilia and colour blindness. 10. One of the examples of two analogous organs can be the wing of parrot and a) Flippers of whale. c)foreleg of horse b) Front leg of frog d)wing of housefly Answer: Wing of housefly SHORT ANSWER QUESTIONS (2 marks) 1. What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering? Answer: The organisms that contain a segment of foreign DNA are known as transgenic organisms. The complimentary property of the nucleotides of DNA.is the most powerful tool in genetic engineering. 2. Explain how the sex of the child is determined at the time of conception in human beings. Answer: Male human beings have XY sex-chromosomes and female human beings have XX sexchromosomes. If a sperm carrying x-chromosome fertilizes with the ovum, then sex of the baby will be female. If a sperm carrying y-chromosome fuses with the ovum, the sex of the baby will be male. 3. By comparing the similarity of nucleotide sequences in DNA of different kinds of organisms, evolutionary relationships can be established. a) Arrange the following according to their evolutionary closeness (You may use your knowledge of classification also) Cockroach, mango tree, gorilla, fish. b) Whose DNA among the following do you think is most similar to that of humans. Answer: a) cockroach fish gorilla b) Gorilla 4. Mention the ways by which variant genotypes are produced in organism? Answer: a) gene mutation b) Crossing over c) Hybridization 5. In human beings blue eye colour is recessive to brown eye colour. If a brown eyed man has a blue eyed mother then find a) What are the possible genotypes of his father? b) What is the genotype of the man and his mother? Answer: BB, Bb B. Man: Bb, mother: bb 6. What are fossils? Of what interest are fossils to the evolutionary biologists? Answer: A fossil is the remnant or impression of an organism that lived in the Remote past. Use of Fossils a) Phylogeny, the evolutionary history can be reconstructed from the fossils. b) The fossil record has helped in building the broad historical sequence of biological evolution. SHORT ANSWER QUESTION (3 marks) 1. a) Who isolated DNA for the first time from pus cells? b) Why is DNA called polynucleotide? c) Name two purine nitrogenous bases found in a DNA molecule. Answer: a) F.Meishcer, named it nuclein. b)dna is called polynucleolide because it is a polymer or long chain of nucleolide. c)purine:- Adenine and Guanine. 2. a) Who put forward the double helical model of DNA?

11 b) What are the three chemically essential parts of nucleotides constituting a DNA? Answer: a) Watson and Crick. b)nucleotide constituting DNA Nitrogen bases (Purines and Pyrimidines), Pentose sugar(deoxyribose sugar) and a phosphate molecule. 3.Guinea pig having black colour when crossed with guinea pig having same colour produced 80 offspring, out of which 60 were black and 20 were white. Now,find out: a)what is the possible genotype of the guinea pigs? b)which trait is dominant and which trait is recessive? c)what is this cross called as and what is its phenotypic ratio? Answer: a) Bb x Bb b)black is dominant and white is recessive. c) Monohybrid cross, phenotypic ratio=3:1 4. Write a brief account on salient points of Lamarck s theory. Who disproved this theory? Answer: Lamarckism 1.The use and disuse of an organ leads to acquiring of change in the features of that organ. 2. These changes are inherited by the offspring. 3. Favourable variations result in evolution of new species. August Weisman disproved this theory. 5. Distinguish between acquired and inherited traits giving one example of each. Answer: Acquired traits 1) A trait (or characteristic) of a organism which is not inherited but develops in response to the environment is called an acquired trait. (2) The acquired traits of an organism cannot be passed on to its future generations. e.g. low weight of beetle, cut tail of a mouse. Inherited traits 1) A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait. 2) The inherited traits of an organism are passed on to its future generations. e.g. red colour of beetles, fur coat of guinea pigs. 6. Why did Mendel chosen pea plant for his experiments? Answer: Mendel chose pea plant for his experiments because it is: (a) Easy to grow (b) Short lifespan (c) Easily distinguishable characters (d) Larger size of flower (e) Selfpollinated. SHORT QUESTION/ANSWERS Q.1. What is heredity? Ans:- Heredity refers to the transmission of characters or traits from the parents to their offspring. Q.2. Name the plant on which Mendel performed his experiments? Ans:- Garden Pea (Pisum sativum.) Q.3. Define variation? Ans:-Variation refers to the differences in the characters or traits about the individuals of a species. Q.4. Define a gene? Ans:- Gene is a small segment of DNA on a chromosome occupying specific position in which is a hereditary determinant or unit of a biological function. Q.5.Write the expanded form of DNA? Ans:- DNA - Deoxyribonucleic Acid. Q.6. What are the components of chromosome? Ans:- Each chromosome is double or replicated and consists of two thread like structures called chromatids attached to each other at centromere. Each chromatid has a number of dense areas arranged linearly which are

12 known as chromomeres. They represent the areas of active genes. Internally each chromosome has two spirally coiled threads called chromonemata embedded in matrix. These are DNA molecules. Q.7. What is a retrovirus? Ans:- A virus having RNA (Ribonucleic acid) as genetic (heredity) material is called Retrovirus. For example, Human immunodeficiency virus (HIV) is a retrovirus. Q.8. What is sex chromosome? Ans:- A chromosome which is associated with sex determination is called sex chromosome. Q.9. How is sex determined in human beings? Ans:- Sex is determined at the time of fertilization and the two sexes are produced in approximately equal numbers. A human male has XY sex-chromosomes and produces two types of sperms (heterogametic). Either with X-chromosome or with Y-chromosome. A human female has XX sex-chromosomes and produce ova of one type (homogametic) all with X-chromosomes. Parents Male Female Gametes X Y X Progeny XX XY Female (50%) Male (50%) Q.10. What do you understand by evolution? Ans:-Evolution is the sequence of gradual changes which takes place in the primitive organisms over million of years in which new species are produced. Q.11. Define homologous organs? Homologous organs are those organs which have the same basic structure and developmental origin but have different functions and appearance. Ans:- e.g., The forelimb of a frog, a bird and a man seem to be built from the same basic design of bones, but they perform different functions. Q.12. Explain Darwin s theory of evolution? Ans:- According to Darwin s theory of evolution: (i) There is natural variation within any population and some individuals have more favourable variations than others.. (ii) Population remains fairly constant even though all species produce a large number of off springs. (iii) This is due to competition or struggle for existence between same and different species. (iv) The struggle for survival within population eliminates the unfit individuals and those with favourable variations survive and pass on these variations to their progeny to continue. This is called natural selection. (v) The favourable variations are accumulated over a long time period leading to the origin of a new species. Q13. Define genetics. What is the contribution of Mendel in this branch of biology? Ans:- genetics is the branch of biology which deals with the study of heredity and variation. Contribution of Mendel : Mendel done his experiments on garden pea(pisum sativum) and discovered the scientific principles which govern patterns of inheritance i.e. the principle of inheritance. He explained the contrasting characters are controlled by units which he called Factors. Today these factors are called genes. Q14. Where are the genes located? What is the chemical nature of gene? Ans:- Genes are located on chromosomes. Chemically, genes are made of DNA(deoxy ribonucleic acid).

13 Q15. During which stage of cell division can chromosome be seen? Write the features of prokaryotic and eukaryotic chromosome. Ans:- Chromosomes can be seen during the metaphase stage of the cell division. FEATURES OF PROKARYOTIC CHROMOSOME: Prokaryotes (bacteria) have a single chromosome. The chromosome is circular and made up of a DNA molecule associated with a few proteins. EUKARYOTIC CHROMOSOME: Eukaryotes contain many chromosomes. Each is made up of a DNA molecule and more number of basic proteins. The chromosomes are not circular but rod shaped. Q 16. Who provided the evidence of DNA as a genetic material? Write the names of components of DNA? Ans:- Griffith, Avery, McLeod and McCarty established that DNA is the genetic material. Components of DNA: A DNA molecule consists of two polynucleotide chains. Each nucleotide consists of (a) nitrogenous base (Adenine/guanine/Thymine or Cytosine),a pentose sugar(deoxyribose) and a phosphate group. Q17.What do you understand by the double helical structure of DNA? Who proposed this structure? Ans:-J.D.Watson & F.H.C.Crick proposed the double helical structure of DNA. The important features of the model are: i)dna molecule consists of two polynucleotide strands forming a double helix. Each helical turn has a length of 3.4nm in which ten nucleotides present. ii)each polynucleotide stand has a backbone of sugar and phosphate. The nitrogenous base is attached to the sugar. iii)the nitrogenous bases of the two stands of a double helix form a pair with the help of hydrogen bonds. Adenine pairs with Thymine,whereas the guanine pairs with Cytosine. Such a specific pairing of the bases is called complimentary pairing. A and T are complimentary to each other and G is complimentary to C. The hydrogen bonding between the nitrogenous bases holds the two strands together as a result of which the base pairs remains stacked between the two strands. This structure can be compared with the steps of a spiral staircase. Q18.Describe the different types of chromosomes. Ans:- depending on the position of the centromere,a chromosome may have either equal arms, or one long and one short arm. Accordingly, four types of chromosomes are known : Metacentric:It is a chromosome with the centromere near the middle and the two arms are almost equal in length. Sub-metacentric:In this type of chromosome the centromere is situated closer to one end. As a result, one arm of the chromosome is long and one is slightly short. Acrocentric:It is the type of the chromosome which has the centromere near the end. In this case one arm is very long and the other one is very short. Telocentric:In this type of the chromosome, the Centromere is situated at the tip of the chromosome. Q19.How many types of nitrogenous bases are present in DNA?Name them. Ans:-In DNA two types of nitrogenous bases are present. These are (i)purines which are adenine and guanine (ii)pyrimidines which are Thymine and cytosine. Q.20.How do embryological studies provide evidence for evolution? Ans:- The similarities in embryonic development reinforce the idea of evolution from common ancestors. The sequence of embryonic development in different vertebrates shows striking similarities. Notochord and gill clefts appear in the embryos of all vertebrates. Q.21. Define evolution. And Describe the contribution of Lamarck? Ans:- Evolution is the sequence of gradual changes which takes place in the primitive organisms over millions of years in which new species are produced. Contribution of Lamarck: (i) Lamarck proposed a theory called The Theory of inheritance of Acquired Characters to explain the origin and evolution of species.

14 (ii) The theory was explained in his book Philosophic Zoologique. Q.22. What are homologous organs? How do they provide evidence in support of evolution? Ans:- Homologous organs are those organs which have the same basic structure and developmental origin but have different functions and appearance. Homologous organs support evolution: (i) The similarities of structure and origin of organs indicate that all vertebrates had common ancestors. For example, the forelimbs of humans, whale and bat show structural similarities but functional dissimilarities. Forelimbs in humans used for grasping or holding the things, in whale for swimming and in bat for flying. (ii) All the organs and systems of the vertebrates show fundamental similarities i.e. homology, which indicate towards common ancestry. Thus, homologous point that organic evolution has taken place. Q.23. Define the following terms? Ans:- (i) Vestigial organs: Vestigial organs are those organs, which are rudimentary and functionless in the evolved forms but are well developed and functional in the ancestral forms. Eg: Vermiform appendix in human beings. (ii) Analogous organs : Are those organs which have different basic structure and developmental origin but have similar appearance and perform similar functions. Eg: The wings of and insect and a bird have different structures, but they perform the same function of flying. Q What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering? Ans:-The organisms that contain a segment of foreign DNA are known as transgenic organisms.the complimentary property of the nucleotides of DNA.is the most powerful tool in genetic engineering. Q.25. Explain how the sex of the child is determined at the time of conception in human beings. Ans:- Male human beings have XY sex-chromosomes and female human beings have XX sex-chromosomes. If a sperm carrying x-chromosome fertilizes with the ovum, then sex of the baby will be female. If a sperm carrying y-chromosome fuses with the ovum, the sex of the baby will be male. Q1)Define evolution. Ans-It a slow gradual process which occurs due to cumulative effects of adaptations and helps it to survive in a better way. Q2)How are fossils helpful in developing evolutionary relationships? Ans: Fossils forms a connecting link between groups of organisms. Q3)Cat s paw,human hand and horse s legs-are these organs homologous or analogous? Give reason Ans- They are homologous organs as they are of same origin performing different functions.origin is forearm modified. Q4)Wings of bird and wings of insect-are these organs homologous or analogous?give one suitable season to support your answer. Ans-They are analogous organs as both have developed from different origin and perform same function of flying. Q5)Give one difference between eyes and eye spot.which animal possesses eye spots? Ans-eyes are well developed organs helping to form an image, but eye spots just enable the animal to distinguish between day light and darkness.e.g. planaria and euglena possess eye spots Q6) Give one difference between artificial selection and natural selection. Ans-Artificial selection is that in which man selects the beneficial gene and modifies it according to his requirement whereas in natural selection nature selects the advantageous gene and helps it to multiply. Q7) What is true- humans have evolved from chimpanzees or humans and chimpanzees both have evolved from a common ancestor? Ans- Both have evolved from a common ancestor because both are existing today.man has not replaced chimpanzees. Q8) What is the mechanism behind the expression of a particular trait? Explain briefly. Ans - The mechanism behind the expression of trait is the presence of a functional gene. When gene is

15 functional it is capable of producing a hormone or enzyme which helps in expression of that trait. But sometimes genes get altered and become non-functional, then the enzyme is not produced and the trait does not get expressed. Q9) What will happen to the expression of a particular trait if a gene get altered? Ans - When gene gets altered the corresponding enzyme is not produced, hence the hormone related to it is not produced and the particular trait does not expressed. There are chances that instead a disease may be seen due to altered gene Q10) What are various ways by which genes can enter a population? Ans. The various way are a) GENE MIGRATION is gene flow which occurs when some members of main population migrate to other areas and may not come back.this is geographical isolation. b) GENETIC DRIFT -is change in gene frequency due to chance or accident and not by natural selection. c) NATURAL SELECTION-is a process in which better quality genes selected by nature are allowed to multiply. d) MUTATIONS arise suddenly- they are sudden changes in the gene inherited by offspring s for at least 4-6 generations. Q11) How will new species arise in case: a) Two sub-populations are separated due to a huge mountain in between them? b) A small population of individuals gets drifted away from the main land due to sea? Ans. New species will arise; a) The huge mountain acts as a geographical barrier and the members of the two sub-population will not be able to mate with one another due to this mountain.this will keep mating within the members of their own subpopulation and hence two new species will arise. b) when the small population gets drifted away from main land by sea, here also chances are that there may be some kind of gene flow between the partly separated populations, but if the two populations do not meet, chances are that two new species would arise. Q12) Only advantageous variations help in the evolution of an organism giving rise to a new species. Explain with the help of an example. Ans. This is because the advantageous variations are selected by nature and allowed to multiply or propagate fast to increase their members. Because such variations help an individual to survive in a better manner in changing environment the population increases. this can be explained as under A- EVOLUTION OF EYE which has occurred bit by bit and not in one step. Even the rudimentary eye was advantageous to Planaria or Octopus even though a clear image was not formed as in humans still it gave a fitness advantage. B-EVOLUTION OF WING-earlier feathers were formed to provide warmth to the body, later these feathers helped in flying. Type-II SHORT ANSWER QUESTIONS (2 marks) 1. What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering? Ans. The organisms that contain a segment of foreign DNA are known as transgenic organisms. The complimentary property of the nucleotides of DNA.is the most powerful tool in genetic engineering. 2. Explain how the sex of the child is determined at the time of conception in human beings. Ans. Male human beings have XY sex-chromosomes and female human beings have XX sex-chromosomes. If a sperm carrying x-chromosome fertilizes with the ovum, then sex of the baby will be female. If a sperm carrying y-chromosome fuses with the ovum, the sex of the baby will be male. 3. By comparing the similarity of nucleotide sequences in DNA of different kinds of organisms, evolutionary relationships can be established. a) Arrange the following according to their evolutionary closeness (You may use your knowledge of classification also) Cockroach, mango tree, gorilla, fish. b) Whose DNA among the following do you think is most similar to that of humans. Ans. a) cockroach fish gorilla b) Gorilla

16 4. Mention the ways by which variant genotypes are produced in organism? Ans. a) gene mutation b) Crossing over c) Hybridization 5. In human beings blue eye colour is recessive to brown eye colour. If a brown eyed man has a blue eyed mother then find a) What are the possible genotypes of his father? b) What is the genotype of the man and his mother? Ans. BB, Bb B. Man: Bb, mother: bb 6. What are fossils? Of what interest are fossils to the evolutionary biologists? Ans. A fossil is the remnant or impression of an organism that lived in the Remote past. Use of Fossils a)phylogeny, the evolutionary history can be reconstructed from the fossils. b) The fossil record has helped in building the broad historical sequence of biological evolution. SHORT ANSWER QUESTION (3 marks) 1. a) Who isolated DNA for the first time from pus cells? b) Why is DNA called polynucleotide? c) Name two purine nitrogenous bases found in a DNA molecule. Ans. a) F.Meishcer, named it nuclein. b) DNA is called polynucleolide because it is a polymer or long chain of nucleolide. c) Purine:- Adenine and Guanine. 2. a) Who put forward the double helical model of DNA? b) What are the three chemically essential parts of nucleotides constituting a DNA? Ans. a) Watson and Crick. b)nucleotide constituting DNA Nitrogen bases (Purines and Pyrimidines), Pentose sugar(deoxyribose sugar) and a phosphate molecule. 3. Guinea pig having black colour when crossed with guinea pig having same colour produced 80 offspring, out of which 60 were black and 20 were white. Now, find out: a)what is the possible genotype of the guinea pigs? b) Which trait is dominant and which trait is recessive? c) What is this cross called as and what is its phenotypic ratio? Ans.a) Bb x Bb b) Black is dominant and white is recessive. c) Monohybrid cross, phenotypic ratio=3:1 4.Write a brief account on salient points of Lamarck s theory. Who disproved this theory? A. Lamarckism 1.The use and disuse of an organ leads to acquiring of change in the features of that organ. 2. These changes are inherited by the offspring. 3. Favorable variations result in evolution of new species. August Weisman. 5. Distinguish between acquired and inherited traits giving one example of each. Ans. Acquired traits 1) A trait (or characteristic) of a organism which is not inherited but develops in response to the environment is called an acquired trait. (2) The acquired traits of an organism cannot be passed on to its future generations. e.g. low weight of beetle, cut tail of a mouse. Inherited traits 1) A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait. 2) The inherited traits of an organism are passed on to its future generations. e.g. red colour of beetles, fur coat of guinea pigs. LONG ANSWER QUESTIONS (5marks) 1. a. What is genetics?

17 b. Give the common name of plant on which Mendel performed his experiments. c. What for did Mendel use the term factors and what are these factors called now. d. What are genes? Where are the genes located? Ans. A. The branch of biology that deals with the study of heredity and variation. b. Garden pea Pisum sativum. c. The units of inheritance of characters. These factors are now called as genes. d.gene is a hereditary unit, a segment of DNA. It is located on a chromosome at a particular locus or position.