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A homologous series is a group of compounds that differ by a constant unit, generally a methylene (−CH 2 −) group. The reactants undergo a homologation when the number of a repeated structural unit in the molecules is increased. The most common homologation reactions increase the number of methylene (−CH 2 −) units in saturated chain ...
The name "homologous series" is also often used for any collection of compounds that have similar structures or include the same functional group, such as the general alkanes (straight and branched), the alkenes (olefins), the carbohydrates, etc. However, if the members cannot be arranged in a linear order by a single parameter, the collection ...
Homology among DNA, RNA, or proteins is typically inferred from their nucleotide or amino acid sequence similarity. Significant similarity is strong evidence that two sequences are related by evolutionary changes from a common ancestral sequence. Alignments of multiple sequences are used to indicate which regions of each sequence are homologous.
The two pairs of wings of ancestral insects are represented by homologous structures in modern insects — elytra, wings, and halteres. The word homology, coined in about 1656, is derived from the Greek ὁμόλογος homologos from ὁμός homos 'same' and λόγος logos 'relation'.
The two pathways for homologous recombination in eukaryotes, showing the formation and resolution of Holliday junctions. The Holliday junction is a key intermediate in homologous recombination, a biological process that increases genetic diversity by shifting genes between two chromosomes, as well as site-specific recombination events involving integrases.
A tetrad is the association of a pair of homologous chromosomes (4 sister chromatids) physically held together by at least one DNA crossover. This physical attachment allows for alignment and segregation of the homologous chromosomes in the first meiotic division. In most organisms, each replicated chromosome (composed of two identical sisters ...
Acyclic alkenes, with only one double bond and no other functional groups (also known as mono-enes) form a homologous series of hydrocarbons with the general formula C n H 2n with n being a >1 natural number (which is two hydrogens less than the corresponding alkane).
At various steps of these recombination processes, heteroduplex DNA (double-stranded DNA consisting of single strands from each of the two homologous chromosomes which may or may not be perfectly complementary) is formed. During meiosis non-crossover recombinants occur frequently and these appear to arise mainly by the SDSA pathway.