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Half Yearly Examination

Date : _________ Biology (Set-1)

CLASS Duration: 3 Hr. Max. Marks : 70 XII

Section – A 1. Name two stop codons of codon table which are same in all types of species. [½+½]

OR If adenine is 15% in double stranded human DNA then what would be the % of cytosine? 2. How many megaspores are formed by meiosis II during megasporogenesis? [1] 3. Name one virulent strain of Griffith’s experiment. [1] 4. Which stage of mammalian embryo is known for implantation in uterus? [1] 5. Name the scientist who disproved spontaneous generation theory. [1]

OR Who experimentally confirmed Oparin-Haldane theory?

Section – B 6. What will happen if lactose sugar is absent in a bacterial cell? [2]

OR If the sequence of one strand of DNA is written as follows: [1+1] 5'-ATGCATGCATGCATGCATGCATGCATAA-3' (a) Considering this 5’ 3’ sequence of ds-DNA write down the sequence of m-RNA chain

synthesized during transcription. (b) Is there any initiating codon present in this synthesized m-RNA chain? 7. What are the main differences between Turner’s syndrome and Klinefelter’s syndome. [2] 8. (a) How gametes are formed if parent is haploid? [1+1] (b) Identify a and b in the following figures:

9. What does GIFT represent? Define in brief. [1+1]

OR Amniocentesis for sex determination is banned in our country. Is this ban necessary? Comment.

General instruction: 1. This question paper consists of four sections. 2. Sections A, B, C & D consists of 1, 2, 3 and 5 marks each. 3. All questions are compulsory.

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10. Do you think the microspores and pollen grains are the same structures? If they are not same in their structures then what are the differences between them? [1+1]

11. Given below is a sequence of steps of transcription in a eukaryotic cell. Fill up the blanks (1, 2, 3, 4) left in the sequence. [2]

12. State in what ways Stanley Miller simulated the conditions of: [1+1] (a) Primitive atmosphere on earth. (b) Formation of organic molecules of life to prove the theory of chemical evolution.

Section – C 13. Is it possible that child has blood group O but father has blood group A and mother blood

group is B? If answer is yes then work out the genotypes of the parents and the possible genotypes of the other offsprings. [1+2]

14. A. Draw schematic structure of a transcription unit with the polarity of coding and Template strand. [2+½+½]

B. Define the following terms: (i) Promoter site (ii) Anticodon

OR Describe all steps of Griffith’s transformation experiment performed in Mice and conclude the

results. [3] 15. Father is with normal vision but mother is a carrier of colour blindness, calculate the % chance

of colour blindness in son of F1 generation by using Punnett square method. [3] 16. Describe Hardy Weinberg Principle in brief on the basis of population genetics. [3]

OR Explain Miller’s experiment through diagrammatic representation. 17. Draw sectional view of a human seminiferous tubule with six labelings. [3] 18. Explain the process of microsporogenesis (Pollen synthesis) in detail including the diagram of 2

celled pollen. [2+1] 19. Name the genes that constitute an operon. How does lac operon get switched on in the presence

of lactose? [1+2] OR

Show diagrammatically the stages of embryonic development from zygote upto implantation in humans.

20. Identify this diagram and label the following: [3]

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21. Identify the causative agents of the following STD’s: Disease Causative Agent i. Syphilis …………………… [½] ii. Gonorrhoea …………………… [½] iii. Chlamydiases …………………… [½] iv. Trichomoniasis …………………… [½] v. AIDS …………………… [½] vi. Genital Herpes …………………… [½] 22. A. Identify the homology or analogy in the given figure: [1+2]

B. Describe adaptive radiation in brief on the basis of Darwin’s finches. 23. Explain menstruation phase and follicular phase during female menstrual cycle in brief with the

levels of ovarian hormones. [3] OR

Describe male hormonal feedback mechanism through the secretions of Hypothalamus & Pituitary gland.

24. Given is the cross A performed by Morgan in Drosophila. Answer the following questions on the basis of linkage theory: [1+1+1]

(a) What’s the difference in between y w and y+ w+ genes in cross A? (b) If parental type genes are 98.7% in cross A then what would be the % of recombinant type

genes? (c) Why Morgan selected Drosophila for his research?

Section – D 25. Describe Hershey & Chase experiment in detail with requirements through diagrammatic

representation. [5] OR

Explain DNA replication mechanism through replication fork diagram with all necessary enzymes, their activity and steps.

26. Write a detailed note on Darwinism. Give role of Natural Selection in evolution. [2+3] OR

What is vegetative propagation? Give two suitable examples. Distinguish between asexual and sexual reproduction. [1+1+3]

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27. What is spermatogenesis? Briefly describe the process of spermatogenesis through a schematic representation with the ploidy of all respective cells from mother cells to sperms. [1+3+1]

OR Describe Oogenesis from embryonic period till the formation of second polar body.

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Hints/Solutions to Half Yearly Examination

Date : _________ Biology (Set-1)

CLASS Duration: 3 Hr. Max. Marks : 70 XII

1. UAA & UAG OR

If A=15% that means T=15% A+T= 30%, remaining is 70% So, cytosine is 35% . 2. 4 megaspores 3. S strain 4. Blastocyst 5. Louis Pasteur

OR Stanley L. Miller and Harold C. Urey 6. In the absence of lactose active repressor is formed and this active repressor will bind with

operator and hence RNA polymerase will not bind with promoter site thus there will be no transcription and regulation of laz z, lac y & lac a genes.

OR (a) Transcribed m-RNA sequence: 5'-AUGCAUGCAUGCAUGCAUGCAUGCAUAA-3' (b) Yes, initiating codon is present in this sequence in the form of 1st codon. 7. Turner’s Syndrome: The individual is female and it has 45 chromosomes. It’s XO condition. Klinefelter’s Syndome: The individual is male and has 47 chromosomes, It’s XXY condition. 8. (a) Gametes are formed through mitosis. (b) Isogametes of Cladophora (Algae) & Heterogametes of Fucus (Algae) 9. GIFT- Gamete Intra Fallopian Transfer. GIFT is an assisted reproduction technology which helps

in the transfer of an ovum collected from a donor into the fallopian tube of another female who cannot produce ova but can provide suitable environment for fertilization and further development of embryo in the oviducts.

OR Sex determination is banned in our country. Most people in obstetrics and medical genetics do

not support prenatal testing for gender while some other cultures do not agree with that. Certainly in our culture, most of us in the field consider prenatal diagnosis for gender determination to be a misuse of the technology. It is like denying women the right to equality and the right to life on the grounds of gender. It is like telling them that they are not wanted.

10. Microspores and pollen grains are not the same structures. Initially the diploid microspore mother cell divides by meiosis to form 4 haploid microspores which are arranged in tetrads. Each microspore has single haploid nucleus then the nucleus of microspore divides mitotically so that the two haploid. Nuclei are formed inside the spore. The entire cell becomes bicellular by developing a separating wall.

Now the spore is 2 celled (large vegetative cell and small generative cell. This structure is called male gametophyte (Pollen grain).

11. (a) DNA dependent-RNA-Polymerase II. (b) hnRNA (c) mRNA (d) Poly adenylate tail. 12. (i) By circulating four gases – methane, ammonia, hydrogen and water vapour in air tight

apparatus.

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(ii) Used electrical discharges as the source of energy. (iii) He found organic compounds including amino acids such as alanine, glycine and aspartic

acid were formed. 13. Yes it will be possible if both father and mother have heterozygous genes of blood group A and

B.

Ratio is AB : B : A : O (1 : 1 : 1 : 1) 14. (a)

(b) (i) Promoter is a region of DNA that leads to initiation of transcription of a particular

gene. Promoters are located near the transcription start sites of genes, upstream on the DNA.

(ii) Anticodon (The anticodon region of a transfer RNA is a sequence of three bases that are complementary to a codon in the messenger RNA). During translation, the bases of the anticodon form complementary base pairs with the bases of the codon by forming the appropriate hydrogen bonds.

OR In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium

responsible for pneumonia), witnessed a miraculous transformation in the bacteria. During the course of his experiment, a living organism (bacteria) had changed in physical form. When Streptococcus pneumoniae (pneumococcus) bacteria are grown on a culture plate, some produce smooth shiny colonies (S) while others produce rough colonies (R). This is because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not. Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia.

Griffith’s steps are given below:

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15. 25% chance of colour blindness in son. 16. Genetic Equilibrium (Hardy Weinberg Law) Hardy and Weinberg were population geneticists who gave the law that forms foundation of

modern evolutionary theory. Law states that ‘both gene frequency and genotype frequency’ will remain constant from generation to generation in an infinitely large interbreeding population in which mating is random and no selection, migration or mutation occurs.

Hardy Weinberg formula or binomial expression is as follow: (p+q)2 p2 + 2pq + q2 = 1 for 2 alleles A and a p = gene frequency of allele A q = gene frequency of allele a p2 = genotype frequency of genotype AA (Homozygous dominant) q2 = genotype frequency of genotype aa (Homozygous recessive) 2pq = genotype frequency of genotype Aa (Heterozgous)

OR Miller’s experiment:

17.

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18. Microsporogenesis – This is the process of formation of microspores or pollen grains from pollen mother cell

through meiosis. – Each cell of sporogenous tissue serves as microspore mother cell (MMC). – These MMCs undergo meiosis I & II and forms microspores tetrad and become haploid – As anthers mature, microspores of the tetrad separate from each other and develop into

pollen grains. – Each microsporangium contains numerous pollen grains which are released at anther

dehiscence after maturity.

Development of 2 celled pollen. 19. Components of Lac operon (i) Structural genes - There are three structural genes (z, y, a) which transcribe a polycistronic mRNA. - Gene z codes for Beta-galactosidase, that catalyses the hydrolysis of lactose into galactose

and glucose. - Gene y codes for permease, which increases the permeability of the cell to p-galactosides

(lactose). - Gene a codes for transacetylase, that catalyses the transacetylation of lactose into its

active form. When lactose binds to the repressor, there is a change in the configuration of the repressor, i.e.,

it is inactivated. It does not bind to the operator and hence the switch is said to be on; transcription of the structural genes takes place.

OR

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20.

21.

6. Genital herpes - Herpes simplex virus 22. A. Homology B. The evolutionary process which produces new species diverged from a single ancestral

form and adapted to new invaded habitats and to modes of life necessary there, is known as adaptive radiation or divergent evolution.

Divergent evolution is shown by Darwin's finches in Galapagos islands. These finches, to avoid competition, diverged along different lines from a common ancestral stock. They adapted to new invaded habitats and to modes of life necessary in such habitats in showing variations in beak shape, feather colour, etc.

23. The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called

menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.

The cycle starts with the menstrual phase, when menstrual flow occurs and it lasts for 3-5 days. The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina. Menstruation only occurs if the released ouvm is not fertilised. The menstrual phase is followed by the follicular phase. During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. Gonadotropins (LH and FSH) increases gradually during the follicular phase, and stimulates follicular development as well as secretion of estrogens by the growing follicles. Level of progesterone decreases during menstrual and follicular phases.

OR

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24. a. Dominant wild type alleles are represented with (+) sign in superscript e.g y+ w+ and non

dominant are y w. b. 1.3 % (Recombinant type) c. Reason for selecting Drosophila: (i) It is easily available hovering over ripe Mango/Banana fruits where it feeds over

yeast cells present over the fruit surface, (ii) The flies can be reared inside bottles having yeast culture over medium containing

cream of wheat, molasses and agar, (iii) A new generation can be raised within 2 weeks with single mating producing

hundreds of individuals, (iv) The animals can be temporarily inactivated with ether and examined by hand

lens/dissection microscope. (v) Female is distinguishable from male by its larger size and ovipositor at the rear end. (vi) The animals possess four pairs of chromosomes of different sizes. The male fly

possesses XY sex chromosomes while the female has XX chromosomes.

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25.

The unequivocal proof that DNA is the genetic material came from the experiments of Alfred

Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages.

The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell. The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles. Hershey and Chase worked to discover whether it was protein or DNA from the viruses that entered the bacteria. They grew some viruses on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur. Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. Similarly, viruses grown on radioactive sulfur contained radioactive protein but not radioactive DNA because DNA does not contain sulfur. Radioactive phages were allowed to attach to E. coli bacteria. Then, as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender. The virus particles were separated from the bacteria by spinning them in a centrifuge. Bacteria which was infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria. Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses. DNA is therefore the genetic material that is passed from virus to bacteria.

OR In addition to DNA-dependent DNA polymerases, many additional enzymes are required to

complete the process of replication with high degree of accuracy. For long DNA molecules, since the two strands of DNA cannot be separated in its entire length (due to very high energy requirement), the replication occur within a small opening of the DNA helix, referred to as replication fork. The DNA-dependent DNA polymerases catalyse polymerisation only in one direction, that is 5'3' . This creates some additional complications at the replicating fork. Consequently, on one strand (the template with polarity 3'5' ), the replication is continuous, while on the other (the template with polarity 5'3' ), it is discontinuous. The discontinuously synthesized fragments are later joined by the enzyme DNA ligase.

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The DNA polymerases on their own cannot initiate the process of replication. Also the replication does not initiate randomly at any place in DNA. There is a definite region in E. coli DNA where the replication originates. Such regions are termed as origin of replication. It is because of the requirement of the origin of replication that a piece of DNA if needed to be propagated during recombinant DNA procedures, requires a vector. The vectors provide the origin of replication. Further, not every detail of replication is understood well. In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. The replication of DNA and cell division cycle should be highly coordinated. A failure in cell division after DNA replication results into polyploidy(a chromosomal anomaly).

26. Charles Robert Darwin gave the theory of evolution which is popularly called Darwinism. He

went on a sea voyage for five years on his ship called H.M.S. Beagle around the world. After returning back he concluded that existing living forms show similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. Many such life forms do not exist as new life forms arose at different periods of history of earth. There has been gradual evolution of life forms. Every population has developed variation in characteristics which enable them to survive better in natural conditions. Darwin used the word fitness which according to him refers to only reproductive fitness. Those who better fit in an environment leave more progeny than others. Therefore they will survive more and are selected by nature. He called it natural selection and called it a mechanism of evolution.

Some important aspects of Darwinism are – struggle for existence, variations, Natural Selection or survival of the fittest, inheritance of useful variations, formation of new species.

The concept of natural selection is an important feature of Darwin's theory of evolution. We treat evolution as a consequence of natural selection. Natural selection is based on certain observations which are factual. All species have potential to reproduce and their population size would increase if all individuals reproduce successfully. Natural resources are limited. Individuals of a population vary in their characteristics and much of these variations are heritable. Nature selects organisms which fit most to their surroundings while unfit are destroyed. Originally. Herbert Spencer used the phrase 'survival of the fittest' for the first time which Darwin called Natural Selection. According to Darwin variations which are heritable and which make resource utilisation better for few will enable only those to reproduce and leave more progeny. Hence for a period of time over many generations, survivor will have more progeny and there would be a change in population characteristic and new forms will appear.

OR Vegetative propagation (or vegetative reproduction) is the most common form of asexual

reproduction in plants. It is a type of asexual reproduction in which a bud grows and develops into new plant. Bulb, corms, rhizomes, stolons, tubers are some of the organs of vegetative propogation.

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27. The process of sperm synthesis through meiosis is spermatogenesis. Sperm production begins

at puberty and continues throughout life with several hundred million sperms being produced each day. Once sperms are formed, they move into the epididymis, where they mature and are stored.

OR

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The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth. These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle. A large number of these follicles degenerate during the phase from birth to puberty. Therefore, at puberty only 60,000-80,000 primary follicles are left in each ovary. The primary follicles get surrounded by more layers of granulosa cells and a new theca and called secondary follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. It is important to draw your attention that it is at this stage that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.