AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

DUPLICATION

• In a diploid organism, the presence of an additional chromosome segment per nucleus is known as duplication.   
• The extra piece either exists as a free fragment chromosome or is attached to one of the chromosomes in the complement.

 To view "Duplication Mutation Animation"

• The duplications are less deleterious for an individual than the deletions, although individuals carrying duplications show abnormalities in bodily characters.
• Duplication provides additional genetic material potentially capable of giving rise to new genes during the process of evolution.
• An altered phenotypic effect produced by change in position of a gene or a group of genes is called position effect.
• Position effect: When a chromosome rearrangement involves no change in the amount of genetic material but only in the order of genes, the term position effect is used to describe any associated phenotypic alterations that occur along with mutation. Position effect represents a source of genetic variation.
• Position effects on gene expression fall into two classes:
  1. Stable: Eg. Bar eye in Drosophila
  2. Variegated/unstable: Eg. Drosophila w[m4] translocation. (white-mottled-4)
• C.B. Bridges (1936) provided concrete evidence to prove that phenotypic expression of bar eye in Drosophila is due to the duplication of five-banded segment in the X chromosome.