1. What is gene linkage? Demonstrate it with examples.
  2. Write note on linkage groups.
  3. Describe crossing over.
  4. What is linkage map? How are they constructed? Explain.
  5. Give different methods for detection of linkage map.



Define crossing over. Give its significance.

Ans: The exchange of segments between non-sister chromatids of homologous chromosomes during meiosis is called crossing over. It produces variations.

  1. What are linked genes? How can linked gene be separated?

Ans: The genes present on the same chromosomes are called linked genes. Linked genes can be separated by crossing over.

  1. Two genes A and B are linked. The other homologous chromosome contains their a and b allele. Give combination of alleles in gametes with and without crossing over.

Ans: Without crossing over the gametes will be: AB and ab. Without crossing over the gametes can be: Ab, aB.

  1. Differentiate between parental and non-parental combinations. Ans: The gametes formed without crossing show parental

combinations. The gametes formed by crossing over show non-parental combinations.

  1. Define recombination frequency.

Ans: The proportion of recombinant types between two gene pairs as compared to the sum of all combinations is called cross over or recombination frequency.

  1. What is gene map? How is it formed?

Ans: The recombination frequency is directly proportional to the distance between the linked gene loci. Genes can be mapped on a chromosome on the basis of their recombination frequencies. I% of recombination frequency is equal to I unit map distance.



  1. What is the importance of crossing over?

Ans: Crossing over produces genetic variations among offspring. These variations help them to adapt successfully in the changing environment. Thus variations provide raw material for evolution.

  1. Define linkage map.

Ans: A linkage map is a chromosome map of a species that shows the position of its known genes or markers relative to each other, rather than as specific physical points on each chromosome.

  1. What is genetic map unit (m.u.), or a centimorgan?
    It is defined as the distance between genes for which one product of meiosis in 100 is recombinant.
  2. What is Robust method of detection of linkage?

Ans: The robust method for detecting linkage was developed by Haseman and Elston. Mathematical integration and regression principles are used in this method. It is used to detect linkage of uantitative enes with other locus.

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