Question

Short / Long answer type questions
Write an essay on chromosomal aberrations giving their cytological and genetic effects

Answer 1

A chromosomal aberration is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. Chromosomal aberrations are of 4 major types: (a) Deletion (b) duplication (c) inversion and (d) translocation. Such chromosomal aberrations cause changes in chromosomal structure and qualitative alteration of genes. Some of the effects of such alterations are:

• Duplications ensure the perpetuation of genes which are present in a single dose.
  
• Pseudo dominance may be seen: A recessive allele behaves like a dominant allele due to a deficiency. E.g: when a cell has lost a chromosomal segment and a dominant allele present is also lost as a result. In such cases the recessive allele becomes functional.
• Crossover suppressors: Inversions in some cases may lead to suppression of crossing over as the inverted chromosomes. The chromatids formed as a result of such crossing over are non-functional.
• Translocation of chromosomal segments may result in new species and are helpful in plant breeding. E.g: Oenothera formed as a result of translocation of more than one non-homologous chromosome.
• They help in genetic analysis. E.g: translocation, duplications, and deficiencies can be used for gene mapping.