Chromosome map
Chromosome map: The chart of the linear array of genes on a chromosome.
A chromosome map can also refer to the visual appearance of a chromosome when stained and examined under a microscope. Particularly important are visually distinct regions, called light and dark bands, which give each of the chromosomes a unique appearance. This feature allows a person’s chromosomes to be studied in a clinical test known as a karyotype, which allows scientists to look for chromosomal alterations.
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- Chromosome, acentric
Chromosome, acentric: A fragment of a chromosome that lacks a centromere, so that the chromosome is lost when the cell divides.
- Chromosome, acrocentric
Chromosome, acrocentric: A chromosome that has its centromere located near one end of the chromosome. Humans have five pairs of acrocentric chromosomes. Down syndrome is due to an extra acrocentric chromosome (chromosome 21).
- Chromosome, dicentric
Chromosome, dicentric: A chromosome that is abnormal in that it has two centromeres rather than one. Because the centromere is essential for chromosome division, a dicentric chromosome is pulled in opposite directions when the cell divides. This causes the chromosome to form a bridge and then break and be unstable.
- Chromosome, marker
Chromosome, marker: An abnormal chromosome that is distinctive in appearance but not fully identified. A marker chromosome is not necessarily a marker for a specific disease or abnormality, but it can be distinguished under the microscope from all the normal human chromosomes. For example, the fragile X (FRAXA) chromosome was once called the marker X.
- Chromosome, metaphase
Chromosome, metaphase: A chromosome in the stage of the cell cycle (the sequence of events in the life of a cell) when a chromosome is most condensed and easiest to distinguish and so to study. Metaphase chromosomes are often chosen for karyotyping and for chromosome analysis because they are readily seen. However, chromosomes in metaphase […]