Past Entrance Papers

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 (b): Sickle cell anaemia is caused due to point mutation in which at the 6th position of beta globin chain, glutamic acid is replaced by valine. Thus, it is a qualitative defect in functioning of globin molecules.

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\(
\text { 2. (b): }
\)

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(d): Down’s syndrome is an autosomal aneuploidy, caused by the presence of an extrachromosome number 21. 

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(d)

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 (d): Mendel carried out hybridisation experiments on garden pea for 7 years from 1856-1863.

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 (c): Translocation is a chromosomal abnormality caused by rearrangement of parts between nonhomologous chromosomes. It may cause a gene to move from one linkage group to another.

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(a): Genotype of colour blind \(\operatorname{man}-X^c Y\) Genotype of women homozygous \(-\mathrm{XX}\)

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 (d): Polyploidy is the phenomenon of occurrence of more than two sets of chromosomes in the nucleus of a cell. Polyploidy is more common in plants. Polyploidy arises as a result of total non-disjunction of chromosomes during mitosis or meiosis.

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(b): Sickle-cell anaemia is an autosomal recessive genetic disorder. It can be transmitted from parents to the offspring when both the partners are carriers of the gene (or heterozygous).

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(c): When a tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant and the \(F_1\) plants were selfed the resulting genotypes were in the ratio of \(\)1: 2: 1\(\) i.e., Tall homozygous : Tall heterozygous : Dwarf

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(d)

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(a): If in a dihybrid test cross more parental combinations appear as compared to the recombinants in F2 generation, then it is indicative of involvement of linkage. 

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(d): Haemophilia is a sex-linked disease. It occurs due to the presence of a recessive sex linked gene h, which is carried by X-chromosome.

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(b): The phenomenon of expression of both the alleles in a heterozygote is called codominance. The alleles which do not show dominance-recessive relationship and are able to express themselves independently when present together are called codominant alleles. 

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(d)

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(b) : When a colour blind ma xY  a normal woman XX, all of their daughters are carriersn and all of their sons are normal, as marriesshown in following

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 (b) : The ability of a gene to have multiple phenotypic effects because it influences a number of characters simultaneously is known as pleiotropy. The gene having a multiple phenotypic effect because of its ability to control expression of two or more characters is called pleiotropic gene. In human beings pleiotropy is exhibited by syndromes called sickle cell anaemia and phenylketonuria.

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 (a) : Autosomal recessive traits are the traits which are caused by recessive autosomal genes when present in homozygous condition. 

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(c): Linkage is the phenomenon of certain genes staying together during inheritance through generations without any change or separation due to their being present on the same chromosome. 

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(a)

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 (a): Genes are the units of inheritance and contain the information that is required to express a particular trait in an organism. 

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(a)

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(a): The man has blood group A, thus its genotype can either be \(I^A I^A\) or \(I^A I^O\). Similarly, woman can either have \(I^B I^B\), or \(I^B I^O\) genotype. Thus, their

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(b)

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 (d): The abnormal baby has an extra X chromosome, thus it must have been produced by fusion of abnormal XX ovum with a normal X sperm.

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(b): A dominant epistatic allele suppresses the expression of a non-allelic gene whether the latter is dominant or recessive. 

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 (c): It is given that the man had colour blind father, i.e., man’s genotype would be XY.

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 (a): A human female with Turner’s syndrome has single sex chromosome i.e., 44+xo= (45). Such females are called sterile females with rudimentary ovaries. Other associated phenotypes of this condition are short stature, webbed-neck, broad chest, lack of secondary sexual characteristics and sterility. Thus, any imbalance in the copies of the sex chromosomes may disrupt the genetic information necessary for normal sexual development.

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(a): Haemophilia is sex-linked disease which is also known as bleeder’s disease as the patient will continue to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting due to absence of antihaemophiliac globulin or factor VIII (haemophilia – A) and plasma thromboplastin factor IX (haemophilia-B, Christmas disease) essential for it. 

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(b): Amniocentesis is a foetal sex determination test in which amniotic fluid containing foetal cells which surrounds the developing embryo is extracted and cells are tested for chromosomal pattern to identify genetic disorders, if any. Jaundice is not a chromosomal disorder thus cannot be tested by amniocentesis.

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(a): Thalassaemia is an autosomal recessive blood disorder. In the given case, both the partners are unaffected carriers for the gene i.e., have heterozygous genotype Tt. 

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(b): In codominance, both the alleles are able to express themselves independently when present together resulting in a phenotype that is intermediate between both the parental homozygous phenotypes, thereby resembling both of them. E.g., roan coat colour in cattle is a result of co-dominance of alleles for white and red coat colour.

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(b): In codominance, both the alleles are able to express themselves independently when present together resulting in a phenotype that is intermediate between both the parental homozygous phenotypes, thereby resembling both of them. E.g., roan coat colour in cattle is a result of co-dominance of alleles for white and red coat colour.

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 (a): Pedigree analysis is a system of analysis by following the movement and distribution of certain genetic traits in many generations of a family. Pedigree analysis cannot confirm that DNA is the carrier of genetic information because it is an analysis system. For DNA based experiments, molecular biology techniques are used.

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 (b): Down’s syndrome is the trisomy of 21st chromosome in man. Down’s syndrome is characterized by short stature, warty skin, protruding tongue, slanting eyes, with folded eyelids. The affected person’s face presents a typical mongoloid look. 

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 (b): In the given condition the chances of child to be colour-blind is zero percent. 

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(d): The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example which shows incomplete dominance. In a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr), the \(\mathrm{F}_1(\mathrm{Rr})\) was pink. When the \(F_1\) was self-pollinated the \(F_2\) resulted in the following ratio, \(1(\mathrm{RR}) \mathrm{Red}: 2(\mathrm{Rr})\) Pink: 1 (rr) White. Here the genotype ratios were \(1: 2\) \(: 1\) as in any Mendelian monohybrid cross, but the phenotype ratios had changed from the \(3: 1\) dominant recessive ratio to \(1: 2: 1\)

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(c)

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 (a): Test cross is performed to determine the genotype of \(\mathrm{F}_2\) plant. In a typical test cross an organism showing dominant phenotype and whose genotype is to be determined is crossed with one that is homozygous recessive for the allele being investigated, instead of self-crossing. The progenies of such a cross can easily be analysed to predict the genotype of the test organism.

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(a): The increased vigour displayed by the offspring from a cross between genetically different parents is called heterosis. Hybrids from crosses between different crop varieties F1 are often stronger and produce better yields than the original varieties.

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(b): XO type of sex chromosomes determine male sex in grasshoppers. This type of sexdetermination comes under XX-XO type. Its common examples are cockroaches, grasshoppers and bugs. The female has two homomorphic sex chromosomes XX and is homogametic. 

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(a) : In humans, the female has a pair of X chromosome (homogametic composition) and the male has XY chromosomes (heterogametic composition). Therefore, two normal X chromosomes in zygotic cell lead to the birth of a normal human female child.

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(c)

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(a): A record of inheritance of certain genetic traits for two or more generations presented in the form of a diagram or family tree is called pedigree.

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(c): The three alleles \(I^4, I^B\) and \(i\) of gene \(I\) in ABO blood group system can produce six different \(
\text { genotypes and four different phenotypes }
\)

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(d): Linkage is the phenomenon of certain genes staying together during inheritance through generations without any change or separation due to their being present on the same chromosome. Linked genes occur in the same chromosome. Strength of the linkage between two genes is inversely proportional to the distance between the two i.e., two linked genes show higher frequency of crossing over (recombination) if the distance between them is higher and lower frequency if the distance is small.

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(a)

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(c): According to Mendel’s law of dominance, in heterozygous individuals a character is represented by two contrasting factors called alleles or allelomorphs which occur in pairs. Out of the two contrasting alleles, only one is able to express its effect in the individual. It is called dominant factor or dominant allele. The other allele which does not show its effect in the heterozygous individual is called recessive factor or recessive allele. The option (c) in the given question cannot be explained on the basis of law of dominance. It can only be explained on the basis of Mendel’s law of independent assortment, according to which in a dihybrid cross, the two alleles of each character assort independently (do not show any blending) of the alleles of other character and separate at the time of gamete formation. Both the characters are recovered as such in \(\mathrm{F}_2\) generation producing both parental and new combinations of traits.

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(c)

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(a)

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(c)

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(c) : The given situation is an example of incomplete dominance where phenotype found in F1 generation do not resemble either of the two parents.

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(c) : Baldness is a sex influenced trait. The dominance of alleles may differ in heterozygotes of the two sexes. This phenomenon is called “sex influenced dominance”. Gene products of heterozygotes in the two sexes may be influenced differentially by sex hormones.

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(b) : Sickle-cell anaemia is an autosomal hereditary disorder in which erythrocytes become sickle shaped. It is caused by the formation of abnormal haemoglobin called haemoglobin-S. Haemoglobin-S is formed when 6 th amino acid of beta-chain, i.e., glutamic acid is replaced by valine due to substitution. It occurs due to a single nucleotide change A TO T in the beta-globin gene of coding strand. In the normal beta-globin gene the DNA sequence is CCTGAGGAG, while in sicklecell anaemia, the sequence is CCTGTGGAG

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 (b) : ADA deficiency can be permanently cured if the isolated gene from bone marrow cells producing ADA is introduced into cells at early embryonic stages.

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(c) : In \(\mathrm{ABO}\) blood group \(\mathrm{O}\) refers to \(\mathrm{O}\) blood group. It has no antigen ( \(\mathrm{A}\) and \(\mathrm{B})\) on \(\mathrm{RBCs}\).

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 (a): This chart shows inheritance of an autosomal recessive trait like phenylketonuria. An autosomal recessive trait may skip a generation. 

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 (c) : Klinefelter’s syndrome is a genetic disorder in which there are three sex chromosomes, XXY, rather than the normal XX or XY. 

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(d) : As sperms produced are with genotypes \(\mathrm{AB}\), \(\mathrm{Ab}, \mathrm{aB}, \mathrm{ab}\) (two diallelic character) the person must be heterozygous for both genes. So his genotype will be \(\mathrm{AaBb}\).

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(d): Yellow (Y) seeds are dominant to green (y). So a heterozygous yellow seeded plant will have the genotype of (Yy) and a green seeded plant will have genotype of (yy). When these two plants are crossed, the \(\mathrm{F}_1\) generation will have the ratio of yellow : green as \(50: 50\). It is shown as

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(b) : Polygenic (or Quantitative) inheritance is that type of inheritance in which the complete expression of a trait is controlled by two or more genes in which a dominant allele of each gene contributes only a unit fraction of the trait and total phenotypic expression is the sum total of a additive or cumulative effect of all the dominant alleles of genes/polygenes. Human skin colour is an example of such polygenic inheritance which is controlled by three pairs of polygenes \(\mathrm{A}, \mathrm{B}\) and \(\mathrm{C}\). Negro/black colour is due to presence of all the six dominant contributing alleles AABBCC. Very light colour or white colour is due to presence of all six recessive non-contributing alleles aabbcc.

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(c) : Hexaploid wheat is a result of allopolyploidy induced by doubling the chromosome number of the hybrid produced by crossing two different plants. In hexaploid wheat Triticale \(2 n=6 x=42\). So \(x\) stands for basic chromosome number and \(n\) for haploid chromosome number. So, \(n=21\) and \(x=7\) for hexaploid wheat.

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(c) : A common test to find the genotypes of a hybrid is by crossing of one F1 progeny with male parent.

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 (d)

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(c): A congenital disorder is a medical condition that is present at birth. Congenital disorders can be a result of genetic abnormalities, the intrauterine environment, or unknown factors. 

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\(
\text { (a) : Colour blindness is a recessivesex-linked trait. }
\)

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(c) : Cri-du-chat syndrome, also called deletion \(5 \mathrm{p}\) syndrome, (or \(5 \mathrm{p}\) minus), is a rare genetic disorder. Cri-du-chat syndrome is due to a partial deletion of the short arm of chromosome number 5 . The name of this syndrome is French for “cry of the cat,” referring to the distinctive cry of children with this disorder. The cry is caused by abnormal larynx development, which becomes normal within a few weeks of birth. Infants with cri-du-chat have low birth weight and may have respiratory problems. Some people with this disorder have a shortened lifespan, but most have a normal life expectancy.

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(d) : Sickle cell anaemia is an autosomal hereditary disorder in which the erythrocytes become sickle shaped. The disorder or disease is caused by the formation of an abnormal haemoglobin called haemoglobin-S. As found out by Ingram (1958), haemoglobin-S differs from normal haemoglobin-A in only one amino acid 6th amino acid of beta-chain, glutamic acid, is replaced by valine.

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 (a) : Since round seed shape is dominant over wrinkled seed shape and yellow cotyledon is dominant over green cotyledon so RRYY individuals is round yellow and rryy is wrinkled green.

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(a) : The plant having genotype \(\mathrm{AABbCC}\) is heterozygous for only one character B. Number of gametes \(=2^n\), where \(n\) is the heterozygosity.

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(a): The external manifestation, morphological or physiological expression of an individual with regard to one or more characters is called phenotype. For recessive genes, phenotype and genotype are similar. For dominant genes, the phenotype is same for both homozygous states. Phenotype is influenced by environment as well as age. A child definitely differs from adolescent, the latter from adult and an adult from aged one. Many phenotypes are determined by multiple genes. Thus, the identity of phenotype is determined by genotype and environment.

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(a)

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(c) : A test cross involving the crossing of \(F_1\) individual with the homozygous recessive parent. It is done to find out homozygous and heterozygous individuals. So \(\mathrm{AaBb}\), should be crossed with aabb.

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(d) : Glucose-6-phosphate dehydrogenase (G-6PD) deficiency is a group of hereditary abnormalities X linked disorder) in which the activity of the erythrocyte enzyme G-6-PD is markedly diminished leading to haemolysis.

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 (b) : Traits governed by sex-linked recessive genes are: (a) produce disorders in males more often than in females, (b) express themselves in males even when represented by a single allele because Ychromosome does not carry any corresponding alleles, (c) seldom appear in both father and son, (d) fail to appear in females unless their father also possesses the same and the mother is a carrier, (e) female heterozygous for the trait function as carrier and (f) female homozygous for the recessive trait transfer the trait to all the sons.

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 (d): Down’s syndrome is caused by the presence of an extra chromosome number 21 . Both the chromosomes of the pair 21 pass into a single egg.

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 (c)

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(d) : Cretinism occurs due to hyposecretion of thyroid hormones. Haemophilia is a sex linked recessive trait. Cystic fibrosis is also a recessive autosomal disorder resulting in mucus clogging in lungs. Thalassemia involves a gene mutation in the polypeptide chains of haemoglobin.

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(a) : Colour blindness is a recessive sex-linked trait. Since the woman’s father was colour blind. She should be carrier of the colour blind gene \(\left(\mathrm{X}^{\mathrm{C}} \mathrm{X}\right)\). 

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 (b) : Since red fruit colour is dominant over yellow fruit colour and tallness is dominant over shortness.

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(a) : The male human is heterozygous for autosomal gene \(\mathrm{A}\) and \(\mathrm{B}\) and also hemizygous for haemophilic gene \(h\), then his genotype will be \(\mathrm{AaBbX} \mathrm{X}^{\mathrm{b}} \mathrm{Y}\) because haemophilia is a sex linked trait that is present on X-chromosome. 

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(c) : Mendel’s law of independent assortment states that when the parent differs from each other in two or more pairs of contrasting characters, the inheritance of one pair of factor is independent of the other. For the character to assort independently they should be located on separate non-homologous chromosomes. Genes present on the same chromosome show linkage. It means that these characters remain together and thus low numbers of combinations are formed. This phenomenon is called linkage and such genes are called linked genes. So, A and B are linked genes.

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 (b) : Mutation is a sudden alteration of the chemical structure of a gene or the alteration of its position on the ch romosome by breaking and rejoining of the chromosome. It has occured in male parent. But organelles like mitochondria, chloroplast etc. are a part of cytoplasmic inheritance.
Cytoplasmic inheritance is the passage of traits from parents to offspring through structures present inside the cytoplasm of contributing gametes. Plasma genes occur in plastids, mitochondria, plasmids and some special particles like kappa particles, sigma particles, etc. In higher organisms cytoplasmic inheritance is called maternal inheritance because the zygote receives most of its cytoplasm from the ovum. Therefore, cytoplasmic inheritance is usually unparental.So none of the progeny will show mutation.

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(b): In question, where the genotype of the other parent is not mentioned then that should be considered normal. Colour blindness is a recessive sex-linked trait
(i) To find out the genotype of a woman.
Her father is colour-blind \(\backslash\) his genotype is \(\mathrm{X}^{\mathrm{e}} \mathrm{Y}\) and her mother is normal so her genotype is XX.

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(c) : The recessive genes located on \(\mathrm{X}\)-chromosome of humans are always expressed in males eg., colour blindness is a recessive sex-linked trait in which the eye fails to distinguish red and green colours. The gene for the normal vision is dominant. The normal gene and its recessive allele are carried by \(\mathrm{X}\)-chromosomes. In females colour blindness appears only when both the sex chromosomes carry the recessive gene \(\left(\mathrm{X}^c \mathrm{X}^{\mathrm{c}}\right)\). The females have normal vision but function as carrier if a single recessive gene for colour blindness is present \(\left(\mathrm{XX}^{\mathrm{c}}\right)\). However, in human males the defect appears in the presence of a single recessive gene \(\left(\mathrm{X}^c \mathrm{Y}\right)\) because \(\mathrm{Y}\) chromosome of male does not carry any gene for colour vision.

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(b)

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(d) : Mendel worked on seven characters. These characters showed complete independent assortment despite the seven characters chosen by him were present on four chromosomes 1,4,5 and 7 .

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(b) : A reciprocal cross means that the same two parent are used in two experiments in such a way that if in one experiment A is used as the female parent and B is used as the male parent then in the other experiment A will be used as the male parent and B as the female parent. Thus the sources of gametes are reversed. When the F1 individuals obtained in a cross is crossed with the recessive parent, it is called a test cross. When inheritance of two pairs of contrasting character is studied simultaeneously it is called dihybrid cross.

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(c): Sex influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive alleles for the female to show that same trait e.g. pattern baldness, moustaches and beard in males. Sex linked traits are those traits determining genes of which are found on the sex chromosomes. Sex limited traits are the traits which are expressed in a particular sex though their genes also occur in the other sex e.g., milk secretion in mammalian females.

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(b)

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 (c): Down’s syndrome is the example of autosomal aneuploidy. Here, an extra copy of chromosome 21 occurs. As it is an autosomal disease, the offsprings produced from affected mother and normal father should be 50 %

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(c) : According to genic balance theory of sex determination the ratio between the number of X-chromosomes and number of complete sets of autosomes will determine the sex. The X-chromosome is believed to carry female tendency genes, while autosomes carry male tendency genes. Both these sets of genes start functioning and there has to be a balance between them for an individual to become male or female. If the ratio between X and A is 1.0 it will be a female individual and when it is 0.5 , it would be male.

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(c) : Pleiotropic gene is such a gene which has a wider effect on phenotype i.e., it controls several phenotypic traits. Sickle cell anaemia is considered to be caused by one such pleiotropic gene. It is caused due to mutation in beta-globin gene of haemoglobin.

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(a): Linkage/ Cross over/ Chromosome maps is a graphic representation of relative positions/ order and relative distances of genes in a chromosome in the form of line like a linear road map depicting different places and their relative distances without giving exact mileage. It is based on Morgan’s hypothesis (1911) that frequency of crossing over/recombination between two linked genes is directly proportional to the physical distance between the two. 1 map unit or centrimorgan is equivalent to \(1 \%\) recombination between two genes. Percentage of crossing over between \(a\) and \(b\) is \(20 \%\) so they are 20 map distance apart and \(b\) and \(c\) are 28 map distance apart. So, that correct sequence of genes on

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(a) : Selfing is the process of fertilisation with polar or male gametes of the same individual. \(\mathrm{AABbCC}\) will produce two type of gametes \(\mathrm{ABC}\) and \(A b C\). Thus, in \(\mathrm{F}_2\) generation three genotypes will be obtained. These are \(\mathrm{AABBCC}, \mathrm{AABbCC}\) and \(A A b b C C\) in the ratio of \(1: 2: 1\). Phenotypically \(\mathrm{AABBCC}\) and \(\mathrm{AABbCC}\) are same. So the phenotypic ratio in \(\mathrm{F}_2\) generation will be \(3: 1\).

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 (c) : Dominant factor is an allele or Mendelian factor which expressess itself in the hybrid (heterozygous) as well as in homozygous state. It is denoted by capital letter.

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(a) : In the inheritance pattern of sex chromosomes X-chromosome of father always passes to daughter and X-chromosome of mother passes to son. As the father is diseased and all the girls inherit it, it is obvious the disease is sex-linked. The mother is not a carrier (as evident from the fact that no son is diseased). Thus, the gene is dominant and expresses even in heterozygous condition.

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(a) : Down’s syndrome (Mongolian Idiocy, Mongolism) is caused by the presence of an extra chromosome number 21. Sickle cell anaemia is not a sex linked (i.e., X linked) disease but an autosomally inherited recessive trait.

Haemophilia is X-linked but not holandric Y-linked. Parkinson’s disease is a degenerative disease. It is not at all hereditary.

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(a): Epistasis is the phenomenon of suppression of phenotypic expression of gene by a non-allelic gene which shows its own effect. The gene which masks the effect of another is called epistatic gene while the one which is suppressed is termed hypostatic gene. Epistasis is of three types – dominant, recessive and dominant-recessive.

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(b): The tendency of potential combinations to remain together, which is expressed in terms of low frequency of recombinations (new combinations) is called linkage. Genes present on same chromosomes show linkage. These genes are called linked genes. Since A and B genes are linked they will be passed on together in the progeny.

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 (a)

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(d) : If two genes present on different loci produce the same effect when present alone but interact to form a new trait when present together, they are called complementary genes. The F2 ratio is modified to 9: 7 instead of 9: 3: 3: 1.

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(b): According to law of independent assortment, the two factors of each trait assort at random and independent of the factors of other traits at the time of meiosis and get randomly as well as independently rearranged in the offspring. 

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(b)

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(c) : Barr body is a mass of condensed sex chromatin in the nuclei of normal female somatic cells due to inactive X chromosome. Whenever the number of X-chromosomes is two or more than two, the number of barr bodies is one less than the number of X-chromosomes. Therefore, the number of barr bodies in XXXX female is three.

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(b) : Male XX and female XY sometimes occur due to transfer of segments in X and Y chromosomes. Deletion is the loss of an intercalary segment of a chromosome which is produced by a double break in the chromosomes followed by the union of remaining parts. Aneuploidy is a condition of having fewer or extra chromosomes than the normal genome number of the species.

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(c)

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(d)

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(a)

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 (a): If fertilization takes place between gametes of Rh female and Rh male then the resulting foetus’ blood is Rh. The Rh+ blood of the foetus stimulates the formation of anti Rh factors in the mother’s blood. In second pregnancy (with Rh foetus), the anti Rh factors of the mother’s blood destroy the foetal red blood corpuscles. This is called erythroblastosis foetalis. New born may survive but it is often anaemic. The Rh- child does not suffer.

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 (a) : Y-chromosome does not play any role in determination of sex in Drosophila. In human being, XXY is phenotypically male with underdeveloped testes, gynecomastia and often mental retardation. It is caused by the union of a non-disjunct XX egg and sperm and a normal X egg and abnormal XY sperm. This indicates that in human being Y chromosome is active in sex determination.

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 (c) 

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(c) : Crossing of individuals having dominant phenotype with its homozygous recessive is a test cross.

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(d) : Colour blindness is produced by a recessive gene which lies on \(\mathrm{X}\) chromosome. A marriage between normal visioned man \((\mathrm{XY})\) and colour blind women \(\left(\mathrm{X}^c \mathrm{X}^{\mathrm{c}}\right)\), results in colour blind sons \(\left(\mathrm{X}^c \mathrm{Y}^{\mathrm{c}}\right)\) and carrier daughters \(\left(\mathrm{XX}^{\mathrm{c}}\right)\).

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(d): A protein named as rhesus antigen, is present on the surface of red blood corpuscles. Persons having this rhesus antigen (Rh factor) are called \(\mathrm{Rh}\) positive \(\left(\mathrm{Rh}^{+}\right)\). Others who do not have this factor are known as \(\mathrm{Rh}\) negative \(\left(\mathrm{Rh}^{-}\right)\). Both \(\mathrm{Rh}^{+}\)and \(\mathrm{Rh}^{-}\)individuals are phenotypically normal. The problem arises during blood transfusion and pregnancy.

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(d) : Haemophilia is caused by a recessive gene located in the X-chromosome. When a haemophilic man \(\left(\mathrm{X}^{\mathrm{h}} \mathrm{Y}\right)\) marries a normal woman (XX), produces carrier girls \(\left(\mathrm{XX}^{\mathrm{h}}\right)\) and normal boys \((\mathrm{XY})\), i.e. all their offsprings will be normal.

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(b)

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(b) : The ability of a gene to have multiple phenotypic effect because it influences a number of characters simultaneously is known as pleiotropy.

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(a) : According to principle of independent assortment, the two factors of each trait assort at random and independent of the factors of other traits at the time of meiosis and get randomly as well as independently rearranged in the offspring. Priniciple of independent assortment is applicable to only those factors or genes which are present on different chromosomes. 

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 (b) : Crossing over is the reciprocal exchange of segments between non-sister chromatids of a pair of homologous chromosomes. It results in recombination of genes.

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(d) : Number of gametes \(=2^n=2^2=4\). where \(n\) is the number of gene in heterozygous form. The four gametes formed will be \(\rightarrow \mathrm{ABc}, \mathrm{AbC}, \mathrm{Abc}\) and \(\mathrm{ABC}\).

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(b) : Both diseases are produced by a recessive gene which lies on the X-chromosomes. A woman having both gene for haemophilia on one Xchromosome and gene for colour blindness on another \(\mathrm{X}\)-chromosome will have genotype \(\mathrm{X}^{\mathrm{h}} \mathrm{X}^{\mathrm{c}}\).

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(d) : In humans, sex chromosomal abnormality is due to gene carried on X-chromosome. Increase in \(\mathrm{X}\)-complement leads to Klinefelter’s syndrome. Klinefelter’s syndrome, 47, XXY or XXY syndrome is a condition caused by a chromosome aneuploidy. Affected males have an extra \(\mathrm{X}\) sex chromosome. It is formed by the union of an XX egg and normal Y sperm or normal X egg and abnormal XY sperm. 

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(d) : Albinism is caused by the absence of the enzyme tyrosinase which is essential for the synthesis of the pigment from dihydroxy-phenyl-alanine. The gene for albinism (a) does not produce the enzyme tyrosinase but its normal allele (A) does. Thus, only homozygous individual (aa) is affected by this disease. Albinos (individuals with albinism) lack dark pigment melanin in the skin, hair and iris. Although albinos have poor vision yet they lead normal life. On the basis of principles of simple recessive inheritance, the probability of albinic child from a normally pigmented parents, will be 1 /4 or 25 %.

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 (c) : The female Drosophila possesses two homomorphic sex chromosomes (XX) and the male Drosophila contains two heteromorphic sex chromosomes (XY). The differential or nonhomologous region of Y-chromosome is mostly heterochromatic. 

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 (b) 

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(a): Sex chromosomes are those chromosomes whose presence, absence or particular form determines the sex of the individual in unisexual or dioecious organisms, e.g., XX – XY. XY method (XX – XY).

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(c)

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 (b) : Complementary genes are those non-allelic genes which independently show a similar effect but produce a new trait when present together in the dominant form. Supplementary genes are a pair of nonallelic genes, one of which produces its effect independently in the dominant state while the dominant allele of the second gene is without any independent effect but is able to modify the effect of the former to produce a new trait. Duplicate genes are independent genes producing the same or similar effect.

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(b)

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 (d): In question where the genotype of the other parent is not mentioned then that should be considered as normal.

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(c)

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(c) : E.B. Lewis in 1951 reported from a cross of apricot eyed and white eyed flies in Drosophila, he obtained \(\mathrm{F}_1\) having intermediate eye colour. In \(\mathrm{F}_2\), he had expected segregation only for apricot and white, but he recovered very low frequency of wild type. Since those alleles behaved as non-alleles, Lewis preferred to call them pseudoalleles and the phenomenon as pseudoallelism.

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 (a)

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(b) : Point mutation involves only the replacement of one nucleotide with another. One type of point mutation is missense mutation. These are base changes that alter the codon for an amino acid resulting in its substitution with a different amino acid. 

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(b)

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 (b) : Despite differences in morphology, the X Y chromosomes are homologous and synapse during zygotene. It is because they have two parts, homologous and differential. Homologous regions of

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(c) : O blood group of a child cannot be obtained from the parents having blood group \(\mathrm{O} \times \mathrm{AB}\). The parents blood groups may be \(\mathrm{A} \times \mathrm{O}, \mathrm{A} \times \mathrm{B}, \mathrm{B} \times \mathrm{O}, \mathrm{B}\) \(\times \mathrm{A}, \mathrm{O} \times \mathrm{A}\) and \(\mathrm{O} \times \mathrm{B}\).

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(a)

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(b)

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(d): The chance of a male child becoming colour blind are possible only when mother’s father was colour blind. It is an example of criss cross inheritance. If a cross is made between two sexes differing in certain characters, in such a way that character of one sex remains hidden in the opposite sex of \(\mathrm{F}_1\) generation,

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(c) : Genotype of Mr. Kapoor will be Bbd hence one fourth of the sperms will have Bd.

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(b) : \(\mathrm{AABB} \times\) aabb is suitable for experiment on linkage. Linkage is the tendency for certain genes tend to be inherited together, because they are on the same chromosome. Thus, parental combinations of characters are found more frequently in offspring than non-parental.

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(c): The gene is located on one X-chromosomes of mother. Cross between a haemophilic carrier female \(\mathrm{X}^{\mathrm{h}} \mathrm{X}\) and normal male would yield \(50 \%\) of the sons being haemophilic and \(50 \%\) of the daughter are carriers.

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(d) : Two dominant non-allelic genes are 50 map units apart. The linkage is absent/incomplete. Chromosome mapping is based on the fact that genes are linearly arranged in the chromosome and frequency of crossing over is directly proportional to the distance between two genes. Dominant genes show cis arrangement. At 50 map units cis is changed to trans and vice-versa hence no fixed linkage is present.

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 (a) 

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 (b) : Law of independent assortment states that when two individuals differ from each other in two or more pairs of factors, the inheritance of one pair is quite independent of the inheritance of other. Law of independent assortment is applicable to only those factors or genes which are located on different chromosomes.

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 (b) : Sex is determined in human beings at the time of fertilisation. Sex of the baby depends upon the sperm which fertilises the ovum.

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(d) : The genotype of the child would be \(\mathrm{I}^{\circ} \mathrm{I}^{\circ}\) (recessive). Hence, the genotype of the father can only be \(\mathrm{I}^{\mathrm{B}} \mathrm{I}^{\mathrm{O}}\).

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(a)

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 (c) : In a cross between \(\mathrm{AABB} \times\) aabb, the ratio of \(\mathrm{F}_2\) genotypes between AABB, AaBB, Aabb and aabb would be \(1: 2: 2: 1\)

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(a) : Segregation of Mendelian factors (no linkage, no crossing over) occurs during anaphase I.

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 (d) : An organism with two identical alleles is homozygous. Homozygous have identical genes at the same locus on each member of a pair of homologous/ chromosomes.