Class 12 AHSEC 2020 Biology Question Paper Solved English Medium

Class 12 AHSEC 2020 Biology Question Paper Solved English Medium, AHSEC Class 12 Biology Question Paper Solved PDF Download, to each Paper is Assam Board Exam in the list of AHSEC so that you can easily browse through different subjects and select needs one. AHSEC Class 12 Biology Previous Years Question Paper Solved in English can be of great value to excel in the examination.

Class 12 AHSEC 2020 Biology Question Paper Solved English Medium

Join Telegram channel

Follow us:

AHSEC Old Question Paper provided is as per the 2020 AHSEC Board Exam and covers all the questions from the AHSEC Class 12 Biology Solved Question Paper 2020 English Medium. Access the detailed Class 12 Biology 2020 Previous Years Question Paper Solved provided here and get a good grip on the subject. AHSEC 2020 Biology Question Paper Solved Access the AHSEC 2020 Biology Old Question Paper Solved, AHSEC Class 12 Biology Solved Question Paper 2020 of English in Page Format. Make use of them during your practice and score well in the exams.

BIOLOGY

2020

BIOLOGY OLD QUESTION PAPER SOLVED

Part – I (Botany)

1. What do you mean by Bt?

Ans: Bt means Bacillus Thuringiensis.

2. What is conidia?

Ans: Conidia is a spore produced asexually by various fungi at the tip of a specialized hypha.

3. Give an example of endomycorrhiza.

Ans: Glomas.

4. What is gene pool?

Ans: The total genetic information of an organism which is present in the protoplasm is known as germplasm. The total genetic information present in a group of interbreeding organism is known as gene pool. 

5. Write on adaptation of nerophytes.

Ans: Adaptation of xerophytes includes deep or widespread roots, and high salt content to increase osmosis. Xerophytes have thick cuticles, lost or finely divided leaves, reduced stomata, and CAM photosynthesis.

6. How plant tissue culture has helped in improvement of crops?

Ans: Tissue culture is a technique where whole plants could be regenerated from explants. Here any plant of a plant is taken out and grown in a test tube, under sterile conditions in special nutrient media. By application of these methods it is possible to achieve propagation of a large number of plants in very short duration. This method of producing a large number of plants is helpful for the production of many important food plants like tomato, banana, apple etc. commercially.

Moreover, this method can be used in the recovery of healthy plants from diseased plants.

Also by isolating protoplasts from two different varieties of plants having a desirable character in fused and can be grown to form a new plant known as somatic hybrids.

Thus it can be said that the tissue culture has helped us in crop improvement as well as its quality is also developed.

7. How is insulin produced through genetic engineering? 

Ans: Insulin is produced through following procedure-

(i) At first suitable vector (plasmid) is isolated from E.Coli and then it is cut open by restriction endonuclease enzyme.

(ii) The gene of interest (ie. insulin coding gene) is isolated from B-cell and inserted in open plasmid.

(ii) Plasmid and gene of interest are recombined together by DNA ligase enzyme.

(iv) The recombined plasmid is inserted into suitable host cell (i.e E.Coli) and now this recombined host cell starts producing insulin hormone.

Or

What is palindrome? Give an example of palindromic sequence.

Ans: Palindrome is a DNA or RNA sequence that reads the same in both directions. Example: 5 – GAATTC – 3 3 – CTTAAG – 5.

8. What is triple fusion? Write the significance of it.

Ans: Secondary nucleus contains two nuclei one from syner gids and the other from antipodal cells. Thus it is already diploid (2n). So when the second male gamete fuses with it during fertilization it become triploid nucleus (3n). This is called triple fusion. 

Triple fusion, i.e. formation of the endosperm is very important for the developing embryo. This is because it provides the embryo with all the nutrition that it needs during the early days of its growth.

Or

Write briefly on artificial vegetative reproduction in plants.

Ans: Artificial vegetative propagation is a type of plant reproduction that involves human intervention. The most common types of artificial vegetative reproductive techniques include cutting, layering, grafting, sucbering and tissue culturing.

9. What is cellular totipotency? What is the importance of it in plant science?

Ans: The capacity to generate a whole plant from any cell of an organism is called totipotency.

Totipotent cells from plants have been used in tissue culture techniques to produce improved plant materials that are pathogen-free and disease-resistant.

10. Explain briefly: (any two)

(i) Genetic therapy.

Ans: Each gene is specific for an enzyme. Therefore for synthesis of every enzyme one gene is required which must be specific for that enzyme. In the absence or defect of a particular gene certain enzyme required to change a metabolic product for the next step to start with not be synthesised. As a result the chain of metabolic reaction which normally ends with production of a substance essential for functioning of the life system stops without completing the chain of reaction. This give rise genetic disease which normally cannot be cured. Gene therapy aims to remove such defect at the embryonic state by injecting correct gene. Permanent cure is still not possible in adult. Bone marrow transplantation, enzyme replacement therapy, infusion of genetically engineered lymphocytes of blood do not bring permanent cure unless treated at embryonic stage. 

In the above scheme the substrate ‘C’ has not changed because the enzyme needed to change it to the next product is not available due to the defect of the gene responsible for its production. Therefore the substrate “C’ will accumulate in the body causing suffering which cannot be cured by any drug. Only gene therapy at the embryonic shape can cure it completely. 

(i) PCR.

Ans: PCR technique was developed by Kary Mullis 1985. If one knows the sequence of at least part of a DNA segment to be cloned, a number or copies of that DNA segment can be hugely amplified using polymerase chain reaction. It is able to generate microgram quantities of DNA copies (up to billion copies) of desired DNA segment, present even as a single copy with short time.

The technique is based on principle that when a DNA molecule is subjected to high temperature due to denaturation the two DNA strands separate. As a result two single stranded DNA molecules appear.

(ii) Endonuclease.

Ans: Endonuclease: These are those enzymes which act upon DNA and cleave them at any point except the ends but they always involve only one strond of DNA.

11. Write the scientific names with their utilities of the following plants: (any three)

(a) Teak.

Ans: Scientific Name – Tectona grandi.

Useful Part – As furniture, home decor -tor etc.

(b) Jute.

Ans: Scientific Name – Corchorus Olitorius. 

Useful Part – Leaf, Seed, Stem. 

(c) Cinchona.

Ans: Scientific Name – Cinchona officinalis.

Useful Part – As medicine of Malaria, painkiller etc.

(d) Tea.

Ans: Scientific Name – Camellia Sinensis.

Useful Part – New Leaf.

12. What is single cell protein (SCP)? Name two algne that are used to produce SCP.

Ans: Single cell protein is one of the alternate sources of proteins for animal and human nutrition.

Some common microbes as SCP produces are- spirulina, Methylophilus, Methylotrophus and Mushroom.

13. What are the advantages of cross-pollination?

Ans: Advantages of cross-pollination:

(i) Offspring may have inherited beneficial qualities from both parents.

(ii) Abundant and more viable seeds tend to be produced.

(iii) More varieties of offspring can be produced.

Or

What is parthenocarpic fruit? How can the formation of such fruits be induced?

Ans: When fruits develop without fertilization it is called parthenogenesis. It leads to production of seedless fruit. Production of seedless fruits is called parthenocarpy. 

Parthenocarpic fruit can be induced in non parthenocarpic varities and in naturally parthenocarpic varities out of season by a type of artificial pollination with dead or altered pollen or by pollen from a different type of plant.

14. Describe the facts on which Darwin’s theory is based.

Ans: Darwin’s theory of evolution is based on the fact that all the different types of species of plants and animals found today are the descendants of common ancestors. Gradual variation among them occured due to changes in organism-environment relationship in both time and space. The organism- environment relationship is different for different populations at different places and time. If a homogeneous population living in a particular environment migrates to a new habitat the organism- environment relationship may change. Depending upon the organism-environmental relationship the nature may select out those combination of genes which are better adapted under the given circumstances. In long course of time a few members of the population may show distinct adaptation which is marked by variation of characters. 

The environment selects out the better gene combination rom the existing gene pool of the population. The newly adapted individual if become reproductively isolated from its parent population, it establishes itself as a new species and breeds among the newly adapted individual. Such a population which is different, even marginally, from its parent population may migrate to new habitat. If the migrated species overcome competition and adapt to a new geographic area and evolve through further specification, the evolutionary line radiating from the initial population to new geographic area is said to have undergone adaptive radiation. 

The adaptive radiation from initial stock first gave rise to races or varieties which had attended the level of species through further adaptation and reproductive isolation. The following two examples will illustrate the concept. 

Darwin’s finches are examples of adaptive radiation from a common ancestor. Galapagos islands are situated on the equator some 900 km. west of Ecuador. These islands were originated form volcanic eruption which were later occupied by plants and animals. A few plants and birds originally entered into the islands and later being separated from the parent stock evolved through selection by nature. Darwin had noticed that there were 13 different species of finches Fish were similar to the species in the mainland. The original species migrated to the new lands which provided greatly relaxed selection pressure because of the absence of predators and competitors. 

The relative isolation of the islànds permitted the establishment of unique hind races or subspecies. From these had arisen the 13 different species. These species had given rise to more subspecies. But the fact that in the mainland there was only one species. So the 13 species had a common ancestor on the mainland. The marine species of giant iguana wizard similarly arose from terrestrial species to avoid competition on land. The finches also to avoid competition developed different food habit and therefore they occupied different ecological places. Their beaks had evolved to suit different kinds of food. 

The homology of forelimbs of mammals illustrates common ancestry. The forelimbs of bat, hale, monkey, pig, horse, mole, ant eater conform to the basic pentadactyl pattern. They were probably originated from common ancestor and evolved in different lines depending upon the need in different ecological niches. 

Or

What is Organic evolution? Write briefly about any one evidence of Organic evolution.

Ans: There are different forms of animals and plants in the nature. The development of new complex living organism both plants and animals on the surface of earth as a result of slow but continuous changes. This mechanism is called the organic evolution. The term evolution mean to hardly change from one form to another (Latin e = out + volvere = to roll).

(a) Evidences from Comparative Anatomy and Morphology: Comparative anatomy of animals provides the most extensive evidences of organic evolution. Though the structure and functions of different organs of animals are varied, the basic pattern of organisation are aim the same in a group or a class of animals or plants. 

A few examples anatomical similarities are as follows: 

(i) Homology: Homologous organs are structurally and ontogenetically similar due to common ancestry but may have varied functions. For example, there appears little similarity between flippers of whale, wings of bats, forelimbs of horse and the hands of human being. All the structures are dissimilar in look and the functions are also quite different. But all these structure possess almost same number of bones, muscles, nerves and blood vessels and their mode of development are also almost similar. All these structures have common origin and are built on the same basic pattern, but due to their adaptation for different functions they are superficially dissimilar. The existence of homologous organs suggests that all these vertebrate animals have inherited the basic structure from 4 common ancestral stock. 

Forelegs of Amphibia 

Flippers of Sea 

Wings of Birds

Wings of Bat 

Forelegs of Horse 

Hands of Human

(ii) Analogy: They have structural differences but have functional (1) similarities means they are coming from the same environment. 

Wings of Bat and wings of Butterfly are the common example of analogous organs. 

(iii) Vestigial Organs: The most convincing morphological evidence of evolution is provide by the vestigial organs. Sometimes an organ which is well developed in one group may be present in rudimentary and functionless condition in another group. Such reduced and functionally useless organs are called vestigial organs. Vestigial organs were once functional and fully developed in the ancestral form but have lost their significance and are reduced structurally in the present form. 

The presence of all these vestigial organs in different animals can only be explained by the fact that the ancestors of these animals had used these organs. Because of the change of environment or mode of life these organs became nonfunctional and so became reduced in size. 

The common vestigial organs of Man are: 

(a) Vermiform appendix.

(b) Coccyx.

(c) Nictitating membrane. 

(d) Wisdom teeth.

(e) Body hair.

(f) Ear muscle.

(g) Abdominal muscle.

(h) Nipples of Male (Man) 

(i) Clitoris of female. 

(b) Evidences from Comparative Embryology: The study of the development of an organism from egg to the adult is known as embryology. Amongst the evidences of organic evolution, the embryological evidences are found to be the most conclusive evidences of evolution. It has been observed that the embryos of different groups of animals have many similarities in their development than the adults. For example, the embryonic development of all groups of vertebrates have striking resemblance during their early stage of development. All multicellular animals start their development is a single zygote. The zygote divides mitotically to form the blastula. The cleavage, blastula and gastrula are almost similar in all the groups of vertebrates. 

Embryos of all groups of vertebrates possess gill pouches in their early development but; functional gills are found only in fishes and in tadpoles of amphibians. The avian and mammalian embryos possess simple tubular heart and same pattern of aortic arches that are found in fishes. The vertebrate embryos possess notochord which is present only in protochordates. 

Why all these structures found only in lower chordates, develop in the embryos of reptiles, birds and mammals? It is because these animals have evolved from a common ancestor. 

(c) Evidences from Palaeontological Records or Geological Evidences: Palaeontology means the study of fossils of ancient plants and animals. The direct evidence of organic evolution is provided by fossils. Fossils provide the missing links in the evolution of the present day flora and fauna. 

Fossil remains are found deep under the soil. They are therefore have to be excavated carefully. Different types of plant and animal fossils have been discovered in different geological strata. Whenever any kind of fossil is discovered in any strata it becomes necessary to ascertain the geological time at which the organism was in existence. It is also necessary to ascertain its evolutionary position by linking it up wich fossils of related forms found in its lower and upper strata in the same place or in other places. It is also necessary to know whether such fossils have been found in other places and in other geological strata. The period in which the animals or plants were existed can be determined by study of fossil records. 

15. Define biotechnology. Write the application of biotechnology in medical science.

Ans: The term “biotechnology” was brought into popular usage in mid 1970s as a result of increased potential for the application of the emerging techniques of molecular biology. Biotechnology is a fast growing applied science. According to definition adopted by European Federation of Biotechnology (1978) “Biotechnology makes it possible, through an integrated application of knowledge and techniques of biochemistry, microbiology, genetics and chemical engineering to draw benefit at the technological level from the properties and capacities of microorganisms and cell cultures.”

Application of biotechnology in medicine:

(i) Genetically Engineered Insulin.

(ii) Gene therapy.

(iii) Molecular Diagnosis-

(a) Polymerase Chain Reaction (PCR).

(b) Enzyme-Linked Immunosorbent Assay (ELISA).

(c) In Situ Hybridisation.

Or

What is plasmid? Write briefly on the main aims of biotechnology.

Ans: Plasmid: The self replicating circular DNA duplex molecules found freely floating in the bacterial cytoplasm are called plasmids. Main aims of biotechnology-

(i) To develop industrial processes for production of antibiotics, enzymes etc.

(ii) To develop gene surgery and gene therapy to cure genetic disease.

(iii) To create improved varities of plants and animals through genetic engineering and plant breeding.

PART – II (Zoology)

1. Fill in the blanks: (any two)

(a) The germinal epithelium of gonads is called ________.

Ans: Epithelial layer.

(b) The animals that are created with genes introduced from other organisms are called________.

Ans: Transgenic organisms.

(c) Gross Primary Productivity – Respiratory losses = ______

Ans: Gross primary productivity (GPP). 

(d) ______is a starting codon.

Ans: AUG.

2. Answer any two:

(a) What is genetic code?

Ans: The genetic code is the set of rules used by living cells to translate information encoded within genetic material into proteins.

(b) What is the function of the mitochondria in sperm?

Ans: The middle pices of sperm contains numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility essential for fertilization. 

(c) What are the coacervates?

Ans: Coacervates are the spherical aggregation of lipid molecules making up a colloidal inclusion which is held together by hydrophobic forces.

(d) In which year the Government of India Promulgated the Environment (Protection) Act?

Ans: 1986. 

3. Answer any four:

(a) What is sex-linked inheritance? Give one example.

Ans: The transmission to successive generations of traits that are due to alleles at gene loci on a sex chromosome is called as sex-linked inheritance.

Example: Colour blindness in human.

(b) Write briefly about ‘Central Dogma’ of molecular biology.

Ans: The process of protein synthesis involves one of the central dogma of molecular biology. According to this, genetic information flows from nucleic acid to protein, the flow of information takes place from DNA to RNA (m RNA) and from RNA to protein.

(c) What is genetic drift? Give one example.

Ans: Genetic drift is a change in the frequency of an allele within a population over time.

For example: A population of rabbits can have brown fur and white fur with brown fur being the dominant allele. By random chance, the offspring may all be brown and this could reduce or eliminate the allele for white fur.

(d) What is ecological niche? Give one example.

Ans: An ecological niche refers to animals place in the biotic environment and its relation to its food and enemies or its functional role in an, ecosystem. No two species can occupy the same ecological niche. If they do occur in the same in the geographical area, then they use different food items or are active at different times or are occupying somewhat different niches. In case, two different species found in the same ecological niche, then only one survives while other is excluded. 

(e) Write your primary signs of Cancer.

Ans: Four signs of cancer:

(i) Persistent cough or blood-tinged saliva.

(ii) Blood in the stool.

(iii) A change in urination.

(iv) Persistent lumps or swollen glands.

(f) What are the characteristics of Acquired Immunity?

Ans: (i) Acquired Immunity is pathogen specific.

(ii) It is characterised by memory acquired in the life time.

4. Write the differences between: (any two)

(a) B-lymphocytes and T-lymphocytes.

Ans: (i) It produces secondary immune responses.

(ii) T-lymphocytes do not produce antibody but it helps to produce antibodies.

(b) Food chain and food web.

Ans: 

(c) Linkage and crossing over.

Ans: Linkage: The tendency of genes to stay together in a chromosome is called genetic linkage. The genes linked together in a chromosome are called the linkage group.

Crossing over: The exchange of genetic material between the non-sister chromatids of a homologous chromosome is called crossing over.

(d) Blastula and Morula.

Ans: 

5. Draw a Labelled diagram of T.S. of ovary.

Ans: 

Draw a Labelled diagram of replicating fork in DNA helix.

Ans: 

6. What is drug? Write about Psychotropic and Psychedelic drugs. 

Ans: Drug is a chemical which people use to give them pleasant or exciting feelings.

A psychotropic describes any drug that affects behaviour, mood, thoughts or perception. Psychedelics are a subcategory of psychotropics, which includes all psychoactive substances.

Or

What is Pisciculture? Write the various types of ponds.

Ans: Farming of pisces is called pisciculture and farming of economical and aquatic organism far human consumption is called aquaculture. 

The various types of ponds are-

(a) Nursery tank.

(b) Hatchery. 

(c) Rearing tank. 

(d) Stocking tank.

7. What is Human Genome Project? Write about the goals of Human Genome Project.

Ans: Human Genome project was an international scientific research project with the goal of determining the sequence of nucleotide base pairs that make up human DNA.

The goals of Human genome projects are: 

(i) Genetic Map: 2 to 5 cm resolution map (600-1500 marker)

(ii) Physical Map: 30,000 sTss. 

(iii) DNA Sequence: 95% of gene containing part of Human sequence finished to 99.99% accuracy. 

(iv) Capacity and Cost of Finished: Sequence 500 Mb/year at <$ 0.25 per finished base. 

(v) Human Sequence Variation: 1,00,000 mapped human SNPs. 

(vi) Gene Identification: Full length human c DNAs (chromosomal DNA). 

(vii) Model Organisms: Complete. 

Or

Write the scientific name of Muga Silk worm. Mention two host plants of Muga Silkworm.

Ans: Muga Silk worm: 

(a) Sc. Name: Antheraea assama.

(b) Primary host plant: Som, Sualu.

8. Describe the structure of Ecosystem.

Ans: A natural unit comprising of living and non-living components, interacting and exchanging materials between them forms a self-dependent and adaptable system known as ecological system or ecosystem. 

The main components of an ecosystem can be classified as: 

(i) Biotic: Includes all the living organisms. 

(ii) Abiotic: Includes all the nonliving components of an ecosystem. 

(iii) Biotic component: These are as follows. 

(a) Producers: These are the green plants which trap solar and convert it to potential chemical energy. These are also known as autotrophs. 

(b) Consumers: All animals and non-green plants which directly or indirectly depend upon the producers for energy from the food. 

(c) Decomposers: These include all micro-organisms which cause decomposition of the dead remains of the plants and animals and utilise a part of the product of decomposition and release the rest of it for use by the producers. Here the decomposers decomposes organic substances to simpler inorganic form. 

(ii) Abiotic factors: The major abiotic factors of an ecosystem includes air, water, soil, light, temperature. 

(a) Air: Air is essential part of an ecosystem. Air means O₂ CO₂, N₂ and other essential components for life. Air should be pure. 

(b) Water: Water is the major constituent of supporter of protoplasm and in an ecosystem water may be present in liquid, vapour and in solid form.

(c) Light: Light is another limiting factor of an ecosystem. It is essential for the growth, development and for the distribution of some animals and plants. 

(d) Temperature: It is also most essential regulating factor for plants and animals in an ecosystem. 

Or

Describe the mechanism of transcription.

Ans: Mechanism of transcription:

(i) Synthesis of mRNA.

(ii) Maturation and movement of mRNA to cytoplasm through nuclear pore.

(iii) Activation of amino acids.

(iv) Transfer of activated amino acid to tRNA.

(v) Formylation of AA₁ – tRNA.

(vi) Attachment of mRNA (S end) with 305 ribosomal sub unit.

(vii) Attachment of f-AA- tRNA net with 305 – mRNA complex to form initiation complex. 

(ix) Association of 505 sub unit to form 705 ribosome.

(x) Binding of AA₁ – tRNA at “A” site of ribosome.

(xi) Elongation of polypeptide chain by addition of amino acids.

9. Describe various Assisted Reproductive Technologies used to solve the Infertility problems.

Ans: Assisted Reproductive Technologies (ART) which include the following techniques: 

(i) Test Tube Baby: The technique of in vitro fertilization and in vitro development followed by the embryo transfer in the uterus of the normal female to start the development and finally leading to normal birth, is called test tube baby. 

(ii) GIFT: Gamete intra fallopian transfer is the technique which is employed for females with prolonged sterility but having at least one patent fallopian tube. It involves the transfer of washed sperms and harvested ova to the ampulla of the fallopian tube with the help of a laparoscope. 

(iii) ICSI: Intra cytoplasmic sperm injection is the technique, where sperm is directly injected into the ovum in culture medium in the lab and then zygote or embryo is transferred in the fallopian tube or uterus of the female. 

(iv) AI: Artificial insemination is the technique where semens of the male partners are collected, concentrated and finally introduced into the vagaina artificially.

Or

Describe the various chromosomal disorder genetic diseases.

Ans: Various genetic diseases are known which are caused by abnormality of the autosomal chromosomes (not connected with determination of sex). Autosomal abnormality may be due to polyploidy (more than normal diploid set of chromosomes) or may be due to aneuploidy (one chromosomes may be more or less than the normal). Aneuploidy has several forms. Sometime 21st pair of 18th pair or 13th pair of chromosomes fail to separate during meiosis. Fertilization between one normal gamete and one abnormal gamete with nondisjunction chromosome gives rise to individual having one extra chromosome such as 3 sets of 21st or 18th or 13th chromosome. This phenomenon is called trisomy. 

Similarly one chromosome of 21st pair or. 18th pair may be deleted. In such condition the diploid cell will contain one chromosome less. This phenomenon is called monosomy. In trisomic condition the body cells contain 47 chromosomes (one chromosome more) but in monosomic condition the body cells contain 45 chromosomes (one chromosome less). Abnormality of sex chromosome also causes genetic diseases of many types. Three or more sets of sex-chromosome results form non-disjunction of sex chromosome during gamete formation. The normal pair of sex- chromosome in human is either XX or XY. But due to abnormality the sex-chromosomes set may be XXY or XYY or XXXY etc. 

Genetic disorder may also be caused by change in the sequence of gene in chromosome. Change in the sequence of gene may be caused by mutagenic agents or may be due to loss of genes by accidental breakage of chromosomal part or it may be due to addition of genes by attachment of broken chromosomal part with another chromosomes. 

Some inherited diseases have been briefly mentioned below: 

(i) Down’s Syndrome: This syndrome is also called mongolism. In the middle aged female the 21st pair of chromosome may not be able to separate during oogenesis. Thus a fertilized egg may contain 3 sets of 21st chromosome. Thereby total chromosomes in the diploid nucleus becomes 47 instead of normal 46. A child having 3 sets of chromosome number 21 (trisomy-21) may suffer from physical and mental defects. Mental retardation is severe in such case. They may have below average height, widely separated eyes, flattened nose, short but broad feet etc. 

(ii) Monosomy-21: If the fertilization egg is devoid of complete set of 21st chromosome the body cell will contain 45 chromosomes. Loss of one chromosome will produce a monosomic child with large ears and closely placed eyes. 

(iii) 18-Trisomy: A Child having 3 sets of 18th chromosome possesses laterally flas head and the helix of the car scarcely develops. The hands are short and show little development of the second phalanx. 

(iv) 13-Trisomy: A child having 3 sets of 13th chromosome shows severe body and organ malformation. Such children are also mentally retarded. Head is small and eyes are often very small or absent. 

Genetic Disorders: 

(i) Mendelian Disorders:

(a) These are mainly due to alternation or mutation in single gene. 

(b) The disorder may be dominant or recessive.

(c) These may be metabolic abnormalities. 

(i) autosomal (eg. sickle-cell anaemia, phenylketonuria) 

(ii) sex-linked (eg. haemophilia, colour blindness) 

(ii) Chromosomal Disorder: 

(a) These may be due to excess of certain chromosome or abnormal arrangement or structural defect of certain chromosome. 

(b) Some of the more serious disorders-Down’s syndrome, Klinefelter’s syndrome, Turner’s syndrome.