Principles of Inheritance and Variation

Linkage and crossing over,mutations


  • Bateson and punnett discovered linkage in Lathyrus odoratus (sweet pea) and stated that certain genes stay together due to their location of same chromosome
  • Sex linkage is discovered by Morgan in drosophila
  • Linked genes do not show independent assortment
  • Males don’t show much crossing over [male drosophila, crossing over is absent]
  • Strength of the linkage ∝ 1/distance between the genes  ∝ 1/crossing over.
  • Temperature and X rays induce crossing over
  • % combination of genes = % crossing over.
  • Complete and Incomplete linkage are the two types of linkages wherein complete linkage, there is no crossing over, whereas in incomplete linkage, non parental combinations occur in meiotic products because of crossing over.
  • If all the dominant genes are located in a single chromatid and all recessive genes located in other pair of chromatid, then the condition is called coupling state (or) cis arrangement
  • If a single chromatid contains both dominant and recessive alleles, then the arrangement is called repulsion (or) trans type.

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