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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 1998 it was determined that homologous pairing in Drosophila occurs through independent initiations (as opposed to a directed, 'processive zippering' motion). [4] [8]The first RNAi screen (based on DNA FISH [9]) was carried out to identify genes regulating D. melanogaster somatic pairing in 2012, [10] described at the time as providing "an extensive “parts list” of mostly novel factors".
Because chromosomal regions composed of transposons have large quantities of identical, repetitious code in a condensed space, it is thought that transposon regions undergoing a crossover event are more prone to erroneous complementary match-up; [33] that is to say, a section of a chromosome containing a lot of identical sequences, should it ...
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.
A pair of homologous chromosomes, or homologs, is a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci , where they provide points along each chromosome that enable a pair of chromosomes to align correctly with each other before ...
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.
Non-random segregation of chromosomes is a deviation from the usual distribution of chromosomes during meiosis, that is, during segregation of the genome among gametes.While usually according to the 2nd Mendelian rule (“Law of Segregation of genes“) homologous chromosomes are randomly distributed among daughter nuclei, there are various modes deviating from this in numerous organisms that ...
[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.