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1.	Explain the mechanism of sex-determination in humans. b) Differentiate between male heterogamety and female heterogamety with the help of an example of each.
Answer» (a) Human female has 44 autosomes + XX sex chromosomes while male has 44 autosomes + XY sex chromosomes. The males produce two types of sperms. 50% of the sperms carry X-chromosome and the other 50% carry Y chromosome. The females produce only one type of gametes (eggs or ovum). All the eggs bear only one, Le. X type of chromosome. When the sperm bearing X-chromosome fuses with egg (ovum during fertilisation to form zygote, such zygote develops into a female baby having XX sex-chromosomes sperm bearing Y-chromosome fuses with egg to form zygote, this zygote gives rise to a male baby having XY sex-chromosome. Thus, in humans, 50 percent chances of a baby boy and 50 percent chances of a baby girl to be bone. In human. it is the sperm which determines the sex of the child (b) In humans we see male heterogamety as human males produce two types of sperms X and Y types. Female heterogamety is seen in birds where female produces two types of egg Z and W while males are homogametic which produce only Z type of sperms

2.	Why are human females rarely haemophilic? Explain. How do haemophilic patients suffer?
Answer» A woman has two X chromosomes, If only one X-chromosome bears an allele for haemophilia, its dominant allele present on the other X-chromosome will not allow the expression of recessive haemophilia allele since haemophilia is a sex linked recessive disease, Such females will be normal but are called carriers for hemophilia gene. This disease occurs mostly in the males because they have one X-chromosome (XY) only Haemophilia is a disorder of the blood which prevents its clotting due to whence of anti-haemophilic globulin. The patient will continue to bleed even from a minor skin cut and as a result of continuous bleeding, he or she may die due to excessive blood loss.

3.	A child suffering from Thalassemia is born to a normal couple. But the mother is being blamed by the family for delivering a sick baby. (a) What is Thalassemia ? (b) How would you counsel the family not to blame the mother for delivering a child suffering from this disease ? Explain... (c) List the values your counselling can propagate in the families.
Answer» (a)Thalassemia is a genetic disease which can be transmitted to the child from any of the parents as its gene is located on a autosome and not on sex chromosome. Father and mother both are equally responsible for transmission of this trait. (ii) If only one parent is the carrier of thalassemia gene, then only some of the offspring may inherit this faulty gene. Since this gene is recessive in nature the child will have thalassemia minor. But in case both the parents are carrier of this defective gene and the child becomes homozygous for this gene, then he will suffer from thalassemia major (c) During the counselling programme, the values that can be propagated in the families are as follows Mothers are not solely responsible for autosomal disorders. In case they have a history of thalassemia in their family they need to go in for genetic counselling. After knowing the scientific principle of this disorder they should seek proper scientific advise for treatment

4.	The following is the flow chart highlighting the steps in DNA finger printing technique. Identify a, b, c, d, e and f.
Answer» a-restriction endonucleases b-electric field c-synthestic membranes, such as nitrocellulose or nylon d-radioactive e-hybridisation f-Autoradiography

5.	By what Latin name, the first Hominid was known?
Answer» Correct Answer - Homo habilis

6.	(a) What is this diagram representing? (b) Name the parts a, b and c. (c) In the eukaryotes the DNA molecules are organized within the nucleus. How is the DNA molecule organized in a bacterial cell in absence of a nucleus?
Answer» (a) A nucleosome (b) a-Core of histone protein, b - DNA. c - Hi Histone respectively (c) In Bacterial cell DNA is organized in large loops held by certain positively charged protein, in a region called nucleoid. DNA is single and circular in nature.

7.	In a maternity clinic, for some reasons the authorities are not able to hand over the two new-borns to their respective real parents. Name and describe the technique that you would suggest to sort out the matter.
Answer» To sort out the matter DNA finger printing of parents and new born are to be conducted to hand over the newborns to their real biological parents. DNA fingerprints can be carried out by taking DNA from extremely minute amounts of blood, semen, hair bulb or any other cells of the body. The major steps are as follows: (i) isolation of DNA from nuclei of cells (ii)If the content is limited, DNA can be amplified using Polymerase Chain Reaction (iii)Digestion of DNA by restriction endonucleases that cuts them into fragments electrophoresis. (iv)Separation of DNA fragments according to their size by gel (v) The separated fragments of DNA in the gel are copied on to a synthetic membranes such as nylon or nitrocellulose by southern blotting technique (vi) Special DNA-probes are made in the laboratory and are made radioactive by labelling with radioactive isotopes. The radioactive DNA probes bind to the repetitive sequences on the nylon membrane (vii) Detection of DNA fragments by autoradiography An X-ray film is exposed to the nylon membrane to mark the places where the radioactive DNA-probes have bound to the DNA fragments. These places are marked as dark bands when X-ray film ts developed. These dark bands on X-ray film represent the DNA fingerprints. Bands of new born will have resemblance with their respective parents

8.	With the advent of DNA technology tool is available to identify a criminal or to the real parents. (a) Name this technique. (b) Write the missing steps in the procedure given below. Three of these steps are mentioned in the flow chart. (i) Extraction of DNA from the cells (ii) .......(iii) DNA is cut into fragments by restriction enzyme (iv) ..... (v)...... (vi). ....(vii) Autoradiography
Answer» (a) DNA finger printing (b) (ii) Amplification by polymerase chain reaction (iv) Separation of DNA fragments by gel electrophoresis (v) Southern blotting (vi) Hybridization using probe-fragment

9.	Unambiguous, universal and degenerate are some of the terms used for the genetic code. Explain the salient features of each one of them.
Answer» (i)One codon of genetic code is for only one amino acid. hence it is unambiguous and specific (ii)Genetic code is universal, as a codon and its corresponding amino acid are the same in all organisms. For example, from bacteria to human UUU codes for phenylalanine (iii)Genetic code is said to be degenerate as more than one codon codes for an amino acid. Such codons differ in only the third base, for example CCU, CCC, CCA and CCG all code for pronine

10.	"A population has been exhibiting genetic equilibrium". Answer the following with regard to the above statement. (i) Explain the above statement. (ii) Name the underlying principle. (iii) List any two factors which would upset the genetic equilibrium of the population. (iv) Take up any one such factor and explain how the gene pool will change due to that factor
Answer» (i)Allele frequencies in the gene pool of a population remains unchanged for generations: (ii) Hardy-Weinberg equilibrium (iii) Any two factors - Mutation/Natural selection / gene flow/genetic drift/ migration. (iv) Mutation changes alleles/Natural selection: brings about greater reproduction of certain alleles

11.	Write the formula to calculate allele frequency in future generations according to Hardy-Weinberg genetic equilibrium.
Answer» `(p+q)^2=p^2+2pq+q^2=1`

12.	Gene flow occurs through generations. Gene flow can occur across language barriers in humans. If we have a technique of measuring specific allele frequencies in different population of the world, can we not predict human migratory patterns in pre-history and history ? Do you agree of disagree ? Provide explanation to your answer.
Answer» Yes, I agree. Gene flow occurs through generations. By studying specie allele frequencies, we can predict the human migratory patterns in prehistory and history. Studies have used specific genes/chromosomes/ mitochondrial DNA to trace the evolutionary history and migratory patterns of humans the project is known as the Human Genographic Project

13.	While creation and presence of variation is directionless, natural selection is directional as it is in the context of adaptation. Comment.
Answer» Creation and variation occur in a sexually reproducing population as a result of crossing over during meiosis and random fusion of gametes. It is however the organisms that are selected over a period of time which are determined by the environmental conditions. n other words, the environment provides the direction with respect to adaptations so that the organisms are more and more fit in terms of survival

14.	Identify the examples of homologous structures from the following- (i) Vertebrate hearts (ii) Thorns in Bougainvillea and tendrils of Cucurbita. (iii) Food storage-organs in sweet potato and potato.
Answer» (i) Vertebrate hearts and (ii) Thorns in Bougainvillea and tendrils of Cucurbita are the examples of homologous structures Homologous structures are the result of divergent evolution and represent those structures which have same structural plan and developmental origin but differ in function they perform

15.	Identify the examples of convergent evolution from the following : (i) Flippers of penguins and dolphins (ii) Eyes of octopus and mammals (iii) Vertebrate brains
Answer» (i)Flippers of penguins and dolphins and (ii) Eyes of octopus and mammals are analogous organs which are a result of convergent evolution, a process by which unrelated species become more similar in order to survive in similar environmental conditions

16.	Explain the increases in the numbers of melanic(dark winged) moths in the urban areas of post-industrialisation period in England.
Answer» In England, it was observed that Biston betularia (peppered moth) showed cryptic colouration with two phenotypes, white (light winged) moths which outnumbered dark black winged moths. After industrialisation the falling smoke particles darkened the background of tree trunk. Against a dark background, the light coloured moths became conspicuous and were picked up by the predator birds the dark coloured moths outnumbered the light coloured moths and they had a much better chance of survival under the new conditions created by industrial pollution. Before industrialisation sel in, thick growth of almost white-coloured the tree. In that background the white winged moth survived but coloured moth were picked up by predators. Thus. industrial melanism demonstrates the action of natural selection

17.	Enumerate three most characteristic criteria for designating a Mendelian population.
Answer» Population must be sufficiently large with potentialities for free flow of genetic material among individuals (through sexual reproduction). Migration should either be nil or negligible.