Duplication of Chromosomal Aberration :ĭuplication represents additions of chromosome parts. Heterozygous deficiencies thus usually decrease the general viability.Ĥ. Recessive genes on the non-deficient chromosome in the region of deficiency may express themselves.

If the deficient cell is a gamete that is subsequently fertilized by a gamete carrying a non-deficient homologue, all cells of the resulting organism will carry the deficiency in the heterozygous condition. Phenotypic effects sometimes indicate which cells or portions of the body have descended from the originally deficient cell. Thus chromosome deficiencies have greatly facilitated the checking of linkage maps.Ī somatic cell that has lost a small chromosome segment may live and produce other cells heterozygous like itself, each with deleted section of a chromosome. This principle of pseudo dominance exhibited by deficiency heterozygotes has been utilized for location of genes on specific chromosomes in Drosophila. In presence of a deficiency, a recessive allele will behave like a dominant allele and this phenomenon is called pseudo dominance. 12.5).ĭeficiencies have an effect on inheritance also. Heterozygous deficiencies during meiosis form a loop in a bivalent and it can be observed in the pachytene stage (Fig. This evidence, presented by Bridges in 1971 in Drosophila melanogaster, showed a deletion of the X-chromosome that included the Bar locus. Deficiency of Chromosomal Aberration :ĭeficiency or deletion represents a loss in chromosomal material and was the first chromosomal aberration indicated by genetic evidence. In cases, where only one chromosome of the pair is structurally altered, the term structural hybrid or hetero- zygote is used (Fig. Structural homozygotes are those in which alterations such as translocation or duplication occur in both the homologous chromosomes and as such termed as translocation homozygote or duplication homozygote. In cases of deletions or deficiencies and duplications, quantitative alterations occur in the chromosome complement, with certain chromosome segments being lost or doubled. All segments are present in the original dosage, but distributed in a new way, i.e. Of the various chromosomal aberrations, inversions and translocations only represent changes in position of chromosome segments of different sizes, the total chromosome mass remaining unchanged. (iv) Translocation (parts of chromosome detached and joined to non-homologous chromosome). (iii) Inversion (sections of chromosome detached and reunited in reverse order), and (ii) Duplication (parts of chromosome added or duplicated), (i) Deficiency (parts of chromosome lost or deleted), Four different kinds of structural changes of chromosome have been demonstrated (Fig.

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