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Principles of Inheritance & Variation Test - 4

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Principles of Inheritance & Variation Test - 4
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  • Question 1
    4 / -1

    In Antirrhinum (dog flower), phenotypic ratio in F2 generation for the inheritance of flower colour would be

    Solution

    The inheritance of flower colour in the Antirrhinum majus (snapdragon or dog flower) is an example of incomplete or partial dominance. Incomplete dominance is the phenomenon in which neither of the two alleles of a gene is completely dominant over the other. In a cross between true-breeding redflowered (RR) and true-breeding white-flowered plants (rr), the F1 plants obtained were pink (Rr) coloured. When the F1 plants were self-pollinated, the F2 generation resulted in the ratio, 1(RR) Red : 2(Rr) Pink : 1(rr) White. The phenotypic ratios had changed from the normal 3:1 dominant : recessive ratio to 1:2:1. R was not completely dominant over r and this made it possible to distinguish Rr (pink) from RR (red) and rr (white).

  • Question 2
    4 / -1

    To determie the genotype of a tall plant of F(2) generation, Mendel crossed this plant with a dwarf plant. This cross represents a

    Solution

    To determine the genotype of a tall plant of F2 generation, Mendel crossed the tall plant from F2 gneration with a dwarf plant. He called this a test cross. In a typical test cross an organism (pea plants) showing a dominant phenotype whose genotype is to be determined is crossed with the recessive parent instead of self-crossing. The progenies of such a cross can easily be analysed to predict the genotype of the test organism. Normal test cross ratio for a monohybrid cross is 1:1 and for a dihybrid cross is 1:1:1:1.

  • Question 3
    4 / -1

    Genes which code for a pair of contrasting traits are known as

    Solution

    Genes are the units of inheritance and contain the information that is required to express a particular trait in an organism. Alternating form if a single gene which code for pair of contrasting traits are known as alleles, i.e, tall and drawf are alleles determining the height of pea plant.

  • Question 4
    4 / -1

    If four o'clock plants, the gene for red flower colour (R) is incompletely dominant over the gene for white flower colour (r), hence the plants heterozygous for flower colour (Rr) have pink flower. What will be the ratio of offsprings in a cross between the red flowers and pink flowers?

    Solution

    Incomplete dominance is reported in flowers of Merabilis jalapa (four o' clock)When red flower are crossed with pink flowers 50 % red flowers and 50 % pink flowers are obtained

  • Question 5
    4 / -1

    What will be the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus?

    Solution

    F1 or first filial or progeny is the generation of hybrids produced from a cross between the genetically different individuals called parents. A cross between homozygous and heterozygous parents for a single locus will produce 1:1 ratio of phenotypic features in F1 generation.

  • Question 6
    4 / -1

    A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents

    Solution

    If father has blood group 'A', mother has blood group 'B', and the child with blood group 'O' appears in progeny, this means that the parents are heterozygous.

  • Question 7
    4 / -1

    Complete the given table showing different possililities of genotypes and their corresponding blood group, by selecting the correct option

    Solution

    • This case where three alleles are present in one gene is called co-dominance, The gene I has three forms and when either A or B is expressed in the gene then either A or B blood group is expressed respectively.
    • When both A and B are present then it results in the AB blood group. The i allele represents the recessive form and codes for O blood group and will be expressed only in the dominant recessive genotype expression.

  • Question 8
    4 / -1

    What is the probability of production of dwarf offsprings in a cross between two heterozygous tall pea plants?

    Solution

    Cross between two heterozygous tall pea plants can be shown as follows:

  • Question 9
    4 / -1

    Inheritance of roan coat in cattle is an example of

    Solution

    Coat colour in short-horned cattle is an exampl of co-dominance. If a cattle with black coat is crossed with a cattle with white coat, the F1 hybrids possess neither black nor white coat colour, but have roan coat colour, where black and white patches appear separately. The effect is produced due to juxtaposition of small patches of red and white colour. Hence the alleles which are able to express themselves independently when present together are called codominant alleles and the inheritance pattern is called co-dominance. On inbreeding, the roan hybrids produce three types of cattle — red, roan and white in the ratio of 1:2:1.

  • Question 10
    4 / -1

    If both parents are carriers for thalassaemia, which is an autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child?

    Solution

    Thalassemia-autosomal-linked recessive
    AA-Normal
    Aa-Carrier
    aa-Disease
    Affected = 1/4 ​= 25%
    An autosomal recessive disorder like thalassemia is caused by abnormalities in both members of a pair of genes. Both parents may carry a single dose of the gene on one chromosome but have a normal gene on the other chromosome, which prevents the appearance of the disease in the carrier parent. A child must get one abnormal gene from each parent in order to be affected by the disease. Parents who are both carriers of an autosomal recessive disorder have a 25% risk of producing an offspring affected by the disease and a 50% risk of producing normal-appearing carriers.

  • Question 11
    4 / -1

    An allele is said to be recessive, when it is expressed in

    Solution

    The factor of an allelic or allelomorphic pair which is unable to express its effect in the presence of its contrasting factor in a heterozygote is called recessive factor or allele, e.g., the allele ′t′ in hybrid tall pea plant Tt. The effect of recessive factor becomes known only when it is present in the pure or homozygous state, e.g., tt in dwarf pea plant.

  • Question 12
    4 / -1

    The characters which appear in the first filial generation are called

    Solution

    In heterozygous individuals or hybrids, out of the two factors or alleles representing the alternate traits of a character, one is dominant and expresses itself in the hybrid or F1 generation. The other factor or allele is recessive and does not show its effect in the heterozygous individual (Principle of dominance).

  • Question 13
    4 / -1

    A tobacco plant heterozygous for a recessive character is self-pollinated and 1200 seeds are subsequently germinated. Flow many seedlings would have the parental genotype?

    Solution

    When heterozygous plants are self-pollinated, 50% of progeny would be parental type. Hence, 600 seeds would have parental genotype.

  • Question 14
    4 / -1

    Which of the following cross will give tall and dwarf pea plants in same proportions?

    Solution

    This is an example of a test cross in which a cross is made between heterozygous tall and homozygous dwarf individuals, tall and dwarf plants are obtained in the same proportions.

  • Question 15
    4 / -1

    In mice, Y is the dominant allele for yellow fur and y is the recessive allele for grey fur. Since Y is lethal when homozygous, the result of cross Yy x Yy will be

    Solution

    Given, that Y is dominant for yellow fur and y is recessive for grey fur, the cross between Yy and Yy will produce ratio of 1YY:2Yy:1yy. But as Y is lethal in homozygous condition, hence phenotypic ratio would be 2 yellow (Yy):1 grey (yy).

  • Question 16
    4 / -1

    Andalusian fowls have two pure forms — black and white. If black forms (BB) and white forms (WW) are crossed, F1 individuals appear blue coloured (BW), due to incomplete dominance. Which of the following would be an outcome of a cross between black form and blue form?

    Solution

    The cross between blue (BW) and black (BB) forms can be shown as :


    Thus, black and blue individuals are produced in the ratio of 1:1

  • Question 17
    4 / -1

    In mice, black coat colour (allele B) is dominant to brown coat colour (allele b). The offspring of a cross between a black mouse (BB) and a brown mouse (bb) were allowed to interbreed. What percentage of the progeny would have black coats?

    Solution

    The cross between black mouse (BB) and a brown mouse (bb) and the inbreeding of their hybrid progeny is shown below

    Hence, phenotypic raio is 3 black : 1 brown i.e, 75 % of the progeny would have black coat.

  • Question 18
    4 / -1

    Read the given statements and select the correct option
    Statement 1: The law of segregation is one of the most important contributions to the biology
    Statement 2: It introduced the concept of heredity factors as discrete physical entities which do not become blended.

    Solution

    The principlem of segregation is the most fundamental principle of heredity that has universal application with no exception. Some workers like Bateson call the principal of segregation as the principle of purity of gametes because segregation of the two Mendelian factors of a trait result result in ametes receiving only one factor out of a pair. As a result gametes are always pure for a character. It is also known as law of non-mixing of alleles and can be demostrated through a monohybrid cross.

  • Question 19
    4 / -1

    In fruit flies, the long wing is dominant to the vestigial wing. When heterozygous long-winged flies were crossed with vestigial-winged flies, 192 offsprings were produced. Of these, 101 had long wings and 91 had vestigial wings. If an exact Mendelian ratio had been obtained, then the number of each phenotype would have been

    Solution

    A cross between heterozygous long-winged flies and (homozygous) vestigial winged flies represents an example of test cross, in which the exact Mendelian ratio of 1:1 is obtained, i.e. 96 long-winged flies and 96 vestigial winged flies.

  • Question 20
    4 / -1

     What can be the blood group of offspring when both parents have AB blood group? 

    Solution

    When both parents have blood group AB(IAIB) then offsprings can have blood groups A(IAIA),B(IBIB) or AB(IAIB) but not O as allele i is not present in any of the parents.

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