1. A. Describe the basic organization units of chromatin. About one third of the
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1. A. Describe the basic organization units of chromatin. About one third of the Drosophila genome is considered heterochromatic. What is constitutive heterochromatin?. B. There are numerous reasons that make Drosophila an excellent model for studying chromatin structure and function. 100 years of Drosophila research has resulted in a wealth of knowledge and has led to the development of highly elaborated experimental techniques rarelv available in other models. Position effect variegation (PEV) analysis is an example that illustrates the above statement. What does PEV analysis study?.Explanation / Answer
1A) Describe basic organization unit of chromatin
The basic organization unit of chromatin is the nucleosome. Chromatin fibers look like a beaded structure. Successive beads are spaced at intervals of approximately 200 base pairs. Chromatin is consisting of repeating 200-base-pair units, known as nucleosomes. Nucleosome core particles resemble like beads.
Recent study showed that Chromatin domains are thought as basic units of chromosome folding and considered as an important secondary structure in chromosome. Each chromosome is located in in a separate chromosome territory in the nucleus. Every chromosome consists of numerous distinct chromatin domains, referred to variably as topological domains. They are hundreds of kilobases to several million bases in length.
Constitutive heterochromatin ?
Constitutive heterochromatin domains are regions of DNA on chromosomes of eukaryotes. They are generally found at the pericentromeric regions of chromosomes, nevertheless some found at the telomeres and throughout the chromosomes. Constitutive heterochromatins are consisting of chiefly satellite repeats, minisatellite, microsatellite repeats, transposon repeats. In Drosophila, more than 450 genes are heterochromatic. Such areas are very condense as well as epigenetically modified so that transcription will not occur.
B) Position Effect Variegation (PEV) analysis study?
Position-effect variegation is a variegation produced by silencing of a gene in certain cells by its abnormal juxtaposition with heterochromatin via rearrangement or transposition.
Comparative analysis of PEV mutations in Drosophila delineates the targets of modifiers.
PEV analysis provides better understandings of properties of heterochromatin.
In Drosophila PEV analysis gave results regarding establishment and maintenance of heterochromatin with concomitant gene silencing.
c) Label Image
Image 1 is white +/+
Image 2 is In(1)white m4
Image 3 is white -/-
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