1q21.1 copy number variations

1q21.1 copy number variations (CNVs) are rare aberrations of human chromosome 1.

In a common situation a human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 CNVs one chromosome of the pair is not complete because a part of the sequence of the chromosome is missing, or overcomplete, because some parts of the sequence are duplicated. The result is that one chromosome is of normal length and the other one is too long or too short.

The structure of 1q21.1 is complex. The area has a size of approximately 6 Megabase (Mb) (from 141.5 Mb to 147.9 Mb). Within 1q21.1 there are two areas where the CNVs can be found: the proximal area or TAR area (144.1 to 144.5) and the distal area (144.7 to 145.9). A 1q21.1 CNV will commonly be found in one of these areas, but an overlap with the other area or parts that are outside these areas are possible. 1q21.1 has multiple repetitions of the same structure (areas with the same color in the picture have equal structures) Only 25% of the structure is not duplicated. There are several gaps in the sequence. There is no further information available about the DNA-sequence in those areas up till now. The gaps represent approximately 700 Kilobase. New genes are expected in the gaps. The area of 1q21.1 is one of the most difficult parts of the human genome to map.

CNVs occur due to non-allelic homologous recombination mediated by low copy repeats (sequentially similar regions).

Four separate forms of 1q21.1 CNVs are mentioned in literature.

The CNVs lead to a very variable phenotype and the manifestations in individuals are quite variable. Some people who have a CNV can function in a normal way, while others have symptoms of mental retardation and various physical anomalies.

Meiosis is the process of dividing cells in humans. In meiosis, the chromosome pairs splits and a representative of each pair goes to one daughter cell. In this way the number of chromosomes will be halved in each cell, while all the parts on the chromosome (genes) remain, after being randomized. Which information of the parent cell ends up in the daughter cell is purely decided by chance. Besides this random process, there is a second random process. In this second random process the DNA will be scrambled in a way that pieces are omitted (deletion), added (duplication), moved from one place to another (translocation) and inverted (inversion). This is a common process, which leads to about 0,4% variation in the DNA. It explains why even identical twins are not genetically 100% identical.

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