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DNA sequences are both necessary and sufficient to specify centromere identity and function in organisms with point centromeres. In budding yeasts, the centromere region is relatively small (about 125 bp DNA) and contains two highly conserved DNA sequences that serve as binding sites for essential kinetochore proteins.
Centromeres are the highly compact regions of chromosomes which join sister chromatids together and also allow the mitotic spindle to attach and separate sister chromatids during cell division. [17] Centromeres are composed of a 177 base pair tandem repeat named the α-satellite repeat. [ 16 ]
The telomere has repetitive junk DNA and hence any enzymatic damage will not affect the coded regions. The areas of the p and q regions close to the telomeres are the subtelomeres, or subtelomeric regions. The areas closer to the centromere are the pericentronomic regions. Finally, the interstitial regions are the parts of the p and q regions ...
However, due to a lack of full centromere assemblies, base-level understanding of satellite array variation and evolution has remained weak. [5] For example, minisatellite DNA is a short region (1-5 kb) of repeating elements with length >9 nucleotides. Whereas microsatellites in DNA sequences are considered to have a length of 1-8 nucleotides. [8]
Other functional regions of the non-coding DNA fraction include regulatory sequences that control gene expression; scaffold attachment regions; origins of DNA replication; centromeres; and telomeres. Some non-coding regions appear to be mostly nonfunctional, such as introns, pseudogenes, intergenic DNA, and fragments of transposons and viruses.
In prophase of mitosis, specialized regions on centromeres called kinetochores attach chromosomes to spindle fibers. The monocentric chromosome is a chromosome that has only one centromere in a chromosome and forms a narrow constriction. Monocentric centromeres are the most common structure on highly repetitive DNA in plants and animals. [1]
R-banding is the reverse of G-banding (the R stands for "reverse"). The dark regions are euchromatic (guanine-cytosine rich regions) and the bright regions are heterochromatic (thymine-adenine rich regions). C-banding: Giemsa binds to constitutive heterochromatin, so it stains centromeres. The name is derived from centromeric or constitutive ...
In contrast, less condensed chromatin (Euchromatin)—which tends to be rich with guanine and cytosine and more transcriptionally active—incorporates less Giemsa stain, and these regions appear as light bands in G-banding. [3] The pattern of bands are numbered on each arm of the chromosome from the centromere to the telomere.