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As the cell divides, the telomeres on the ends of chromosomes shorten. The Hayflick limit is the limit on cell replication imposed by the shortening of telomeres with each division. This end stage is known as cellular senescence. The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes.
The main features of replication origins are sequences where specific initiation proteins are bound. 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 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 : Spindle fibers attach onto both centromeres in different locations on the chromosome, thereby ...
Usually, all cells in an individual in a given species (plant or animal) show a constant number of chromosomes, which constitute what is known as the karyotype defining this species (see also List of number of chromosomes of various organisms), although some species present a very high karyotypic variability. In humans, mutations that would ...
Replication timing is correlated with the expression of genes such that the genetic information being utilized in a cell is generally replicated earlier than the information that is not being used. We also know that the replication-timing program changes during development, along with changes in the expression of genes.
Eukaryotic DNA replication. Eukaryotic DNA replication is a conserved mechanism that restricts DNA replication to once per cell cycle. Eukaryotic DNA replication of chromosomal DNA is central for the duplication of a cell and is necessary for the maintenance of the eukaryotic genome.
Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be aneuploid (from the Greek words meaning "not", "good", and "fold"). Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes. [44]
Junk DNA (non-functional DNA) is a DNA sequence that has no known biological function. [1] [2] Most organisms have some junk DNA in their genomes—mostly, pseudogenes and fragments of transposons and viruses—but it is possible that some organisms have substantial amounts of junk DNA.