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In meiosis, non-sister homologous chromosomes pair with each other so that recombination characteristically occurs between non-sister homologues. In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair .
A typical replication origin covers about 100-200 base pairs of DNA. Prokaryotes have one origin of replication per chromosome or plasmid but there are usually multiple origins in eukaryotic chromosomes. The human genome contains about 100,000 origins of replication representing about 0.3% of the genome. [25] [26] [27]
Non-homologous end joining can also join two different chromosomes together that had broken ends. The reason non-reciprocal translocations are dangerous is the possibility of producing a dicentric chromosome – a chromosome with two centromeres. When dicentric chromosomes form, a series of events can occur called a breakage-fusion-bridge cycle ...
The chromid is smaller than the chromosome, and so takes a shorter amount of time to finish replication. For this reason, replication of the chromid is delayed to coordinate replication termination between the chromosome and chromid. [25] Earlier replication of the chromosome compared with the chromid has also been observed in Ensifer meliloti ...
Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of it happening is a function of the degree of sharing of repetitive elements between two chromosomes. The products of this recombination are a duplication at the site of the exchange and a reciprocal ...
This causes chromosomes to fail to properly segregate in a process called nondisjunction. In turn, nondisjunction can cause sperm and ova to have too few or too many chromosomes. Down's syndrome , which is caused by an extra copy of chromosome 21 , is one of many abnormalities that result from such a failure of homologous recombination in meiosis.
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction.Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart.
The 46/47 annotation indicates that the XY cells have the normal number of 46 total chromosomes, and the XXY cells have a total of 47 chromosomes. Also monosomies can present with some form of mosaicism. The only non-lethal full monosomy occurring in humans is the one causing Turner's syndrome. Around 30% of Turner's syndrome cases demonstrate ...