Genetics, Molecular Biology and Evolution-Linkage and Crossing Over [IFS (Forest Services) Botany]: Questions 1 - 7 of 9

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Question 1

Appeared in Year: 2015

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What are the merits of pedigree methods? (Paper 2, Section A)

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Explanation

What is Pedigree Method?

  • Individual plants are selected from F2 and the subsequent generation and their progenies are tested.
  • Pedigree record is the record of the entire parent՚s offspring relationship in this process
  • Selection of individual plant is continued till the progenies show no segregation.
  • Selection is done among the progenies as there would …

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Question 2

Appeared in Year: 2015

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How will you distinguish cytologically between paracentric inversion and pericentric inversion? (Paper 2, Section A)

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Explanation

Paracentric Inversion

  • Paracentric inversions do not occur in the centromere.
  • Crossing over only occurs in the out the loop in one arm of the chromosome.
  • The result is a large loop in where recombination occurs in only part of the loop.
  • When crossover occurs within the loop, it causes the cells to die during meiosis.
  • This means that the only possible out…

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Question 3

Appeared in Year: 2018

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Describe the molecular mechanism of gene linkage and crossing-over. Explain how gene mapping is constructed using gene linkage with suitable diagrams.

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Explanation

Molecular Basis of Crossing Over

Gene Conversion

  • Gene conversion is the unequal recovery of alleles in the region of exchange during genetic recombination.
  • It results into 3: 1 ratios where normally the ratio is 2: 2 in the meiotic products.

Post Meiotic Segregation

  • In fungi, the four products of meiosis undergo one mitotic division to produce 8 spores.

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Question 4

Appeared in Year: 2021 (IAS)

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Explain coupling and repulsion hypothesis in linkage. Give a brief account of procedure used in preparing a chromosome map with the help of three-point test cross. (Paper-2)

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Explanation

Coupling and Repulsion Hypothesis in Linkage

  • In 1906, Bateson and Punnett described a sweat pea hybrid in which gene pairs failed to assort independently. Plants from one sweat pea variety with blue flowers (BB) and long pollen (LL) were crossed with plants from another type with red flowers (BB) and round pollen (LL) (II) . Individuals from the

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Question 5

Appeared in Year: 2020 (IAS)

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Briefly describe two theories of Chiasma formation. Discuss whether Chiasmata are the cause or consequence of crossing-over.

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Explanation

Chiasma refers to the exchange of segments between non-sister chromatids of homologous chromosomes during meiotic prophase (pleural chiasmata) . It is supposed to be the point at which people pass over. Janssens found chiasma for the first time in 1909. Chiasma is classified into two categories based on its position: terminal and interstitial. When…

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Question 6

Appeared in Year: 2022

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Write a note on: Homologous recombination (Paper 2)

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Explanation

The most significant characteristics of organisms are their ability to adapt to their surroundings and to keep their DNA sequence in cells from generation to generation with minimal changes. Long-term survival of organisms is dependent on genetic variants, a critical trait that allows the organism to adapt to a changing environment.

This variation a…

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Question 7

Appeared in Year: 2020

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How was gene linkage discovered? Describe gene mapping by three-point test cross. (Paper-2)

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Explanation

Describe Gene Mapping by Three-Point Test

The pioneering work of Thomas Hunt Morgan and his associates in the early 20th century is credited with the discovery of gene linkage. Morgan conducted extensive research on Drosophila melanogaster, a fruit fly with a relatively brief generation period, a large number of progeny, and distinct observable char…

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