Linkage and Recombination – Class 12 | Chapter – 5 | Biology Short Notes Series PDF

Linkage and Recombination: Linkage and recombination are phenomena that describe the inheritance of genes. A linkage is a phenomenon where two or more linked genes are always inherited together in the same combination for more than two generations. The recombination frequency of the test cross progeny is always lower than 50%. Therefore, if any two genes are completely linked, their recombination frequency is almost 0%. The phenomenon of linkage was studied by the scientist T.H. Morgan using the common fruit fly or Drosophila melanogaster.

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He chose fruit flies or Drosophila melanogaster due to the reasons mentioned below.

  • One can easily differentiate both the male and female drosophila
  • One single mating is capable of producing many offspring
  • It can easily cultivate in the synthetic medium in the laboratory
  • It has a shorter lifespan of about 2 weeks.
  • Different types of hereditary variations are available.

Linkage and Recombination

Genetic linkage is the tendency of genes located close together on a chromosome to be inherited together. This is because the genes are usually passed on to the next generation as a unit. This is due to the physical proximity of the genes on the chromosome.

Recombination is the process of genes swapping places on a chromosome. Recombination can occur as a result of crossing over, which is when the two strands of a chromosome briefly cross over each other.

Types of Linkage and Recombination

Types Of Linkages

Linkages can be classified into two types established on the absence or presence of non-parental combinations or new combinations, namely:

  • Complete Linkage: A linkage is said to be complete when two or multiple characteristics are inherited and normally surface in two or further generations in their parental or original combinations, they are known as complete linkage. These particular genes do not generate combinations that are non-parental. The genes that exhibit these linkages are located nearby in the same chromosome. Examples – genes for long wings and grey body in male Drosophila
  • Incomplete Linkage: It is displayed by genes that generate some portion of non-parental combinations. These genes are situated at a distance on the chromosomes which can be attributed to the occasional or accidental deconstruction of chromosomal segments while crossing over.

Types Of Recombination

There are three types of Recombination:

  • Homologous Recombination: This type arises between DNA molecules with comparable sequences, as the name implies. During meiosis, the cells undergo widespread recombination.

  • Nonhomologous Recombination: This form of interaction happens between DNA molecules that aren’t necessarily related. There will often be some degree of sequence similarity, but it will not be as clear as it would be in homologous recombinations.

  • Site-specific Recombination: This can be seen between specific, extremely short sequences that are frequently similar.

  • Mitotic Recombination: Mitotic recombination occurs during interphase. However, this type of recombination is usually harmful and can result in tumors. It increases when the cells are exposed to radiation. There are three types of recombination in prokaryotic cells. They are:
    • conjugation
    • transformation
    • transduction

Difference between Linkage and Recombination

Linkage

Recombination

  • Linkage happens when two genes are very close to one another.
  • Recombination occurs when two genes are relatively far apart.
  • The linkage between two genes weakens as the distance between them grows, and recombination through crossing over becomes more common.
  • When the distance between two points diminishes, the likelihood of recombination lowers as well.
  • The inheritance of the same parental features for more than two generations is known as linkage.
  • Recombination is the variation of parental qualities in the next generation to exhibit non-parental traits.
  • It does not support the law of independent assortment.
  • It supports the law of independent assortment.

 


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By Team Learning Mantras