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  Section: Biotechnology Methods » Cell Biology and Genetics
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Chromosomal Aberrations

Cell Biology and Genetics
  Cell Cycles
  Meiosis in Flower Buds of Allium Cepa-Acetocarmine Stain
  Meiosis in Grasshopper Testis (Poecilocerus Pictus)
  Mitosis in Onion Root Tip (Allium Cepa)
  Differential Staining of Blood
  Buccal Epithelial Smear and Barr Body
  Vital Staining of DNA and RNA in Paramecium
  Induction of Polyploidy
  Mounting of Genitalia in Drosophila Melanogaster
  Mounting of Genitalia in the Silk Moth Bombyx Mori
  Mounting of the Sex Comb in Drosophila Melanogaster
  Mounting of the Mouth Parts of the Mosquito
  Normal Human Karyotyping
  Black and White Film Development and Printing for Karyotype Analysis
  Study of Drumsticks in the Neutrophils of Females
  Study of the Malaria Parasite
  Vital Staining of DNA and RNA in Paramecium
  Sex-Linked Inheritance in Drosophila Melanogaster
  Preparation of Somatic Chromosomes from Rat Bone Marrow
  Chromosomal Aberrations
  Study of Phenocopy
  Study of Mendelian Traits
  Estimation of Number of Erythrocytes [RBC] in Human Blood
  Estimation of Number of Leucocytes (WBC) in Human Blood
  Culturing Techniques and Handling of Flies
  Life Cycle of the Mosquito (Culex Pipiens)
  Life Cycle of the Silkworm (Bombyx Mori)
  Vital Staining of Earthworm Ovary
  Culturing and Observation of Paramecium
  Culturing and Staining of E.coli (Gram’s Staining)
  Breeding Experiments in Drosophila Melanogaster
  Preparation of Salivary Gland Chromosomes
  Observation of Mutants in Drosophila Melanogaster
  ABO Blood Grouping and Rh Factor in Humans
  Determination of Blood Group and Rh Factor
  Demonstration of the Law of Independent Assortment
  Demonstration of Law of Segregation

The chromosome of each species has a characteristic morphology and number. But sometimes due to certain irregularities at the time of cell division, crossing over, or fertilization, some alterations in the morphology and number take place. The slightest variation in the organization of the chromosome is manifold, phenotypically, and is of great genetic interest.

The presence of a part of the chromosome in excess of the normal complement is known as duplication. During pairing, the chromosome bearing the duplicated segment forms a loop.

  1. Bar eye in Drosophila. This is characterized by a narrow, oblong bar-shaped eye with few facets.
    It is associated with a duplication of a segment of the X-chromosome called 16A. Each added section intensified the bar phenotype.
  2. A reverse repeat in the chromosome IV causes eyeless (Ey) morphology.
  3. A tandem duplication in chromosome III causes confluens (Co), resulting in thickened veins.
  4. Another duplication causes hairy wing (Hw).
Loss of a broken part of a chromosome is called deletion. Deletion may be terminal or intercalary. During the pairing between a normal chromosome and a deleted chromosome, a loop is formed in the normal chromosome. This is known as the deletion loop.

Notched wing mutation in Drosophila.

In the presence of deletion, a recessive allele of the normal homologous chromosome will behave like a dominant allele (pseudodominance).

Inversion involves a rotation of a part of a chromosome or a set of genes by 180° on its own axis. It essentially involves the occurrence of breakage and reunion. The net result of inversion is neither gain nor loss in the genetic material, but simply a rearrangement of the sequence.
During pairing, an inversion loop is formed, in which one chromosome is in the inverted order and its homologue is in the normal order.

Chromosomes with inversions have practical applications for maintaining Drosophila stock. Crossing over is suppressed in such chromosomes and it is possible to maintain a gene in the heterozygous state that would cause death when present in the homozygous condition.

The shifting of a part of a chromosome or a set of genes to a nonhomologous one is called translocation. During synapsis, a cross-shaped configuration is formed. H.J. Muller found one strain of Drosophila in which a group of genes, including scarlet, which normally is on the third chromosome, translocated to the second chromosome. Cytological examination showed that the third chromosome was much shorter than usual, while the second chromosome was longer than usual.

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