A complex family of repetitive DNA sequences found in the centromeric heterochromatin of human chromosomes. The alphoid family is composed of tandem arrays of 170 base pair segments. The segments isolated from different chromosomes show a consensus sequence, but also differences with respect to individual bases, so that the 170 base pair units may vary in sequence by as much as 40%. The repeats are organized in turn into groups containing several units in tandem, and these groups are further organized into larger sequences 1 to 6 kilobases in length. These large segments are then repeated to generate segments 0.5 to 10 megabase pairs in size. Such larger, or “macro,” DNA repeats are chromosome-specific. Since alphoid sequences are not transcribed, they play an as yet undefined structural role in the chromosome cycle. The variation in the sequences within the alphoid DNA results in a high frequency of RFLPs. These are inherited and can be used to characterize the DNAs of specific individuals and their relatives. See DNA fingerprint technique, restriction fragment length polymorphisms.
Subjects: Genetics and Genomics.