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 […]
- Chromosome, X
Chromosome, X: The sex chromosome found twice in normal females and once, along with a Y chromosome, in normal males. The complete chromosome complement (consisting of 46 chromosomes, including the 2 sex chromosomes) is thus conventionally written as 46,XX for chromosomally normal females and 46,XY for chromosomally normal males. The X chromosome not only determines […]
- Chromosome, Y
Chromosome, Y: The sex chromosome found in normal males, together with an X chromosome. Once thought to be a genetic wasteland, the Y chromosome is now known to contain at least 20 genes. Some of these genes are unique to the Y chromosome, including the male-determining gene and male fitness genes that are active only […]