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Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speciation event (orthologs), or a duplication event (paralogs), or else a horizontal (or lateral) gene ...
Alignments of multiple sequences are used to indicate which regions of each sequence are homologous. [40] Homologous sequences are orthologous if they are descended from the same ancestral sequence separated by a speciation event: when a species diverges into two separate species, the copies of a single gene in the two resulting species are ...
In genetics, a locus (pl.: loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. [1] Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at ...
The pseudoautosomal regions or PARs are homologous sequences of nucleotides found within the sex chromosomes of species with an XY [1] or ZW [2] mechanism of sex determination. The pseudoautosomal regions get their name because any genes within them (so far at least 29 have been found for humans) [3] are inherited just like any autosomal genes.
Crossovers typically occur between homologous regions of matching chromosomes, but similarities in sequence and other factors can result in mismatched alignments. Most DNA is composed of base pair sequences repeated very large numbers of times. [29] These repetitious segments, often referred to as satellites, are fairly homogeneous among a ...
The filament searches for the homologous chromosome, strand invasion occurs where the new chromosome forms a D-loop over the bottom sister chromatid, then the ends are annealed. This process can yield double Holliday junctions that when cut in a transversal pattern by endonucleases form 2 heteroduplex strand products.
The two domains differ in sequence content and extent of homology to other chromosome ends, and they are often separated by a stretch of degenerate telomere repeats (TTAGGG) and an element called 'core X', which is found at all chromosome ends and contains an autonomously replicating sequence (ARS) and an ABF1 binding site.
In humans these regions account for about 200Mb or 6.5% of the total human genome, but their repeat composition makes them difficult to sequence, so only small regions have been sequenced. Visualization of constitutive heterochromatin is possible by using the C-banding technique .