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KVPY Sample Paper KVPY Stream-SX Model Paper-3

  • question_answer
    \[Igf2\] Gene of mouse encodes for insulin like growth factor II. A mouse that carries two normal wild type alleles of this gene is normal in size, whereas a mouse that carries two mutant alleles is dwarf. One heterozygous male was crossed with a heterozygous female, both being normal sized. The ratio of normal to dwarf was \[1:1\] instead of the expected \[3:1\] when some of these \[{{\operatorname{F}}_{1}}\] male dwarfs were mated with homozygous mutant female dwarfs, normal mice appeared in the following progeny. This can happen if the normal \[Igf2\] gene got imprinted in parent during

    A) Egg production only.

    B) Sperm production only.

    C) Either egg or sperm production.

    D) Both egg and sperm production.

    Correct Answer: A

    Solution :

    [a]
    Let allele for insulin like growth factor II is represented as\[I\].
    Genotype\[II\] = Normal size
    Genotype \[ii\] = Dwarf
    Cross 2
    Parents:\[ii\,\,\,\,\left( \operatorname{XX} \right)\times Ii\,\,\,\left( \operatorname{XY} \right)\]
    Offspring:
    \[I\left( X \right)\] \[i\left( X \right)\]
    \[I\left( \operatorname{X} \right)\] \[II\left( XX \right)\]normal size \[Ii\left( XX \right)\]normal size
    \[i\left( Y \right)\] \[Ii\left( XY \right)\] Dwarf  \[ii\left( XY \right)\] Dwarf
    Cross 2
    Parents: \[ii\,\,\left( \operatorname{XX} \right)\times Ii\,\left( \operatorname{XY} \right)\]
    Offspring:
    \[i\,\left( \operatorname{X} \right)\] \[i\,\left( \operatorname{X} \right)\]
    \[I\,\left( \operatorname{X} \right)\] \[\mathbf{I}i\,\left( \operatorname{XX} \right)\]Normal size \[\mathbf{I}i\,\left( X\operatorname{X} \right)\]Normal size
    \[i\,\left( Y \right)\] \[i\,\mathbf{i}\left( \operatorname{XY} \right)\] Dwarf \[i\,\mathbf{i}\left( \operatorname{XY} \right)\] Dwarf
    From cross 2, normal mice appeared due to activation of allele\[I\]in the progeny received from male parent so normal \[Igf2\]gene did not get imprinted during sperm production. From cross 1, since some of the males were dwarfs heterozygous), so normal \[Igf2\]gene received from the female parent got imprinted during egg formation.


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