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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 ...
In organic chemistry, a homologation reaction, also known as homologization, is any chemical reaction that converts the reactant into the next member of the homologous series. A homologous series is a group of compounds that differ by a constant unit, generally a methylene ( −CH 2 − ) group.
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. [1] Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.
Although the basic chemical reaction is the same for both tyrosine and serine recombinases, there are some differences between them. [13] Tyrosine recombinases, such as Cre or FLP, cleave one DNA strand at a time at points that are staggered by 6–8bp, linking the 3' end of the strand to the hydroxyl group of the tyrosine nucleophile (Fig. 1 ...
[citation needed] While in this formation, homologous sites on two chromatids can closely pair with one another, and may exchange genetic information. [ 6 ] Because there is a small probability of recombination at any location along a chromosome, the frequency of recombination between two locations depends on the distance separating them.
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.
Sequences are either homologous or not. [3] This involves that the term "percent homology" is a misnomer. [4] As with morphological and anatomical structures, sequence similarity might occur because of convergent evolution, or, as with shorter sequences, by chance, meaning
The 5’ strand is then cleaved, either by XPF-ERCC1 or another endonuclease, forming a double-strand break (DSB), which can then be repaired by the homologous recombination pathway. [17] The repair of interstrand crosslinks requires both nucleotide excision repair and homologous recombinational repair. [18].