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History of genetics
Learn introductory genetics with Braimy- B.Sc agriculture
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a) Deletion or deficiency:

  • Deletion or deficiency as the name suggests there is a loss of segment of chromosome.
  • After break the part without centromere is lost. On the other hand, the part attached to the centromere acts as deficient chromosome.
  • It causes following effects:

i) Recessive lethality

ii) Pseudodominance

iii) lack of revertability

b) Duplication:

  • Here a segment of chromosome is repeated twice, i.e., duplicated.
  • Duplication was discovered in Drosophila ‘X’ chromosome for the first time carrying wild type allele for vermilion (v+) and has been transposed to an ‘X’ chromosome carrying the mutant vermilion allele (v), Bridges found that due to the fact that ‘X’ chromosome was carrying allele v and v+ both it was wild type instead of vermilion.
  • It is of following types:

i) Tandem duplication: When the duplicating segment is near the centromeres.

ii) Reverse tandem: When the segment is reversed in duplication.

iii) Displaced tandem: The segment is repeated somewhere away from its original location but on the same arm (homobrachial displacement) or on the other arm (heterobrachial displacement).

iv) Transposition: When the segment is duplicated on the non-homologous chromosome it is called transposition.

v) Extra chromosomal: Duplication involves centromere it is called extra chromosomal. In salivary gland chromosome duplications are common either as buckling in the duplication heterozygote or as cross pairing between sections of different chromosomes.

Chapter 14 Human Inheritance - ppt video online download

c) Translocation:

  • Transfer of a section of one chromosome to non-homologous chromosome is known as translocation.
  • When there is exchange of segments on two non-homologous chromosomes it is called reciprocal translocation.


  • It is of following types:

i) Simple translocation: A single break in the chromosome and it is transferred onto the end of the other.

ii) Shift or intercalary translocation: Common type of translocation involving 3 breaks so that a two-break section of one chromosome (e.g., Pale) is inserted within the break produced in a non-homologous chromosome.

iii) Reciprocal translocation or Interchange: Frequently observed translocation where single break in two homologous chromosomes produces an exchange of chromosome segment between them.

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