on activity, ie. constitutive heterochromatin that is Repetitive-sequence DNA includes the moderately and highly repeated sequences. They may be tightly condensed in virtually all cell types and dispersed throughout the genome or clustered in facultative heterochromatin which varies between cell tandem repeats. Heterochromatin is rich in moderate types and/or developmental stages. and highly repetitive DNA. Other methods of characterizing types of DNA Human DNA contains about 65% unique sequences suggest that there are sequences of DNA that can occur while unque sequence DNA makes up a much lower in may copies in the genome. These types of sequences percentage of the genome of organisms that have can be repeated only once in the genome or they can unexpectedly large genomes (C-values) that were occur 10’s of thousans of times or more in genomes. discussed earlier in this section. Sequences can be categorized into: Unique-sequence DNA, present in one or a few copies per genome. Moderately repetitive DNA, present in a few to 105 copies per genome Highly repetitive DNA, present in 105–107 copies As Watson and Crick were solving the structure of per genome DNA, they realized the general mechanism by which the Observations repetitive DNA sequences as molecule could be copied and maintain fidelity in described above have been known for decades, and copying the DNA molecule. From that beginning, initially it was shown that Prokaryotic DNA was mostly interest in understanding the duplication of the DNA unique-sequence DNA, and Prokaryotes had little or no molecules of a cell became a subject of investigation, repetitive sequences. However, Eukaryotes have a mix and led to a number of Nobel Prize awards. However, of unique and repetitive sequence types of DNA. understanding DNA replication was critical to the Unique-sequence DNA includes most of the genes development of the technologies needed for molecular that encode proteins, and Euchromatin is rich in genetics and ultimately genomic biology research. unique-sequence DNA.
on activity, ie. constitutive heterochromatin that is tightly condensed in virtually all cell types and facultative heterochromatin which varies between cell types and/or developmental stages. Other methods of characterizing types of DNA suggest that there are sequences of DNA that can occur in may copies in the genome. These types of sequences can be repeated only once in the genome or they can occur 10’s of thousans of times or more in genomes. Sequences can be categorized into: Unique-sequence DNA, present in one or a few copies per genome. Moderately repetitive DNA, present in a few to 105 copies per genome Highly repetitive DNA, present in 105–107 copies per genome Observations repetitive DNA sequences as described above have been known for decades, and initially it was shown that Prokaryotic DNA was mostly unique-sequence DNA, and Prokaryotes had little or no repetitive sequences. However, Eukaryotes have a mix of unique and repetitive sequence types of DNA. Unique-sequence DNA includes most of the genes that encode proteins, and Euchromatin is rich in unique-sequence DNA. Repetitive-sequence DNA includes the moderately and highly repeated sequences. They may be dispersed throughout the genome or clustered in tandem repeats. Heterochromatin is rich in moderate and highly repetitive DNA. Human DNA contains about 65% unique sequences while unque sequence DNA makes up a much lower percentage of the genome of organisms that have unexpectedly large genomes (C-values) that were discussed earlier in this section. As Watson and Crick were solving the structure of DNA, they realized the general mechanism by which the molecule could be copied and maintain fidelity in copying the DNA molecule. From that beginning, interest in understanding the duplication of the DNA molecules of a cell became a subject of investigation, and led to a number of Nobel Prize awards. However, understanding DNA replication was critical to the development of the technologies needed for molecular genetics and ultimately genomic biology research.
ch3-MolecularGenetics_1.2.docx