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Wilmington, North Carolina once had a thriving Black middle class and an elected interracial government. In 1898 white supremacists used violence to overthrow that government, kill Black residents and drive many others from the city.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
In genetics, a dynamic mutation is an unstable heritable element where the probability of expression of a mutant phenotype is a function of the number of copies of the mutation. That is, the replication product (progeny) of a dynamic mutation has a different likelihood of mutation than its predecessor. These mutations, typically short sequences repeated many times, give rise to numerous known diseases, including the trinucleotide repeat disorders.
Robert I. Richards and Grant R. Sutherland called these phenomena, in the framework of dynamical genetics, dynamic mutations. Triplet expansion is caused by slippage during DNA replication. Due to the repetitive nature of the DNA sequence in these regions, 'loop-out' structures may form during DNA replication while maintaining complementary base pairing between the parent strand and daughter strand being synthesized. If the loop-out structure is formed from sequence on the daughter strand this will result in an increase in the number of repeats. However, if the loop-out structure is formed on the parent strand a decrease in the number of repeats occurs. It appears that expansion of these repeats is more common than reduction. Generally the larger the expansion the more likely they are to cause disease or increase the severity of disease. This property results in the characteristic of anticipation seen in trinucleotide repeat disorders. Anticipation describes the tendency of age of onset to decrease and severity of symptoms to increase through successive generations of an affected family due to the expansion of these repeats.
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In genetics, a dynamic mutation is an unstable heritable element where the probability of expression of a mutant phenotype is a function of the number of copies of the mutation. That is, the replication product (progeny) of a dynamic mutation has a different likelihood of mutation than its predecessor. These mutations, typically short sequences repeated many times, give rise to numerous known diseases, including the trinucleotide repeat disorders. Robert I. Richards and Grant R. Sutherland called these phenomena, in the framework of dynamical genetics, dynamic mutations. Triplet expansion is caused by slippage during DNA replication. Due to the repetitive nature of the DNA sequence in these regions, 'loop-out' structures may form during DNA replication while maintaining complementary base pairing between the parent strand and daughter strand being synthesized. If the loop-out structure is formed from sequence on the daughter strand this will result in an increase in the number of repeats. However, if the loop-out structure is formed on the parent strand a decrease in the number of repeats occurs. It appears that expansion of these repeats is more common than reduction. Generally the larger the expansion the more likely they are to cause disease or increase the severity of disease. This property results in the characteristic of anticipation seen in trinucleotide repeat disorders. Anticipation describes the tendency of age of onset to decrease and severity of symptoms to increase through successive generations of an affected family due to the expansion of these repeats.
In genetics, anticipation is a phenomenon whereby as a genetic disorder is passed on to the next generation, the symptoms of the genetic disorder become apparent at an earlier age with each generation. In most cases, an increase in the severity of symptoms is also noted. Anticipation is common in trinucleotide repeat disorders, such as Huntington's disease and myotonic dystrophy, where a dynamic mutation in DNA occurs. All of these diseases have neurological symptoms. Prior to the understanding of the genetic mechanism for anticipation, it was debated whether anticipation was a true biological phenomenon or whether the earlier age of diagnosis was related to heightened awareness of disease symptoms within a family.
The Sherman paradox was a term used to describe the anomalous pattern of inheritance found in fragile X syndrome. The phenomenon is also referred to as anticipation or dynamic mutation.
A trinucleotide repeat expansion, also known as a triplet repeat expansion, is the DNA mutation responsible for causing any type of disorder categorized as a trinucleotide repeat disorder. These are labelled in dynamical genetics as dynamic mutations. Triplet expansion is caused by slippage during DNA replication, also known as "copy choice" DNA replication. Due to the repetitive nature of the DNA sequence in these regions, 'loop out' structures may form during DNA replication while maintaining complementary base pairing between the parent strand and daughter strand being synthesized. If the loop out structure is formed from the sequence on the daughter strand this will result in an increase in the number of repeats. However, if the loop out structure is formed on the parent strand, a decrease in the number of repeats occurs. It appears that expansion of these repeats is more common than reduction. Generally, the larger the expansion the more likely they are to cause disease or increase the severity of disease. Other proposed mechanisms for expansion and reduction involve the interaction of RNA and DNA molecules. In addition to occurring during DNA replication, trinucleotide repeat expansion can also occur during DNA repair. When a DNA trinucleotide repeat sequence is damaged, it may be repaired by processes such as homologous recombination, non-homologous end joining, mismatch repair or base excision repair. Each of these processes involves a DNA synthesis step in which strand slippage might occur leading to trinucleotide repeat expansion. The number of trinucleotide repeats appears to predict the progression, severity, and age of onset of Huntington's disease and similar trinucleotide repeat disorders. Other human diseases in which triplet repeat expansion occurs are fragile X syndrome, several spinocerebellar ataxias, myotonic dystrophy and Friedreich's ataxia.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Joe Louis.
