Robertsonian translocation

[1] It does not usually cause medical problems, though some people may produce gametes with an incorrect number of chromosomes, resulting in a risk of miscarriage.

Detailed DNA studies of chimpanzee, orangutan, gorilla and bonobo apes has determined that where human chromosome 2 is present in our DNA in all four great apes this is split into two separate chromosomes typically numbered 2a and 2b.

[citation needed] This type of translocation may involve homologous (paired) or non-homologous chromosomes.

The short arms also join to form a smaller reciprocal product, which typically contains only nonessential genes also present elsewhere in the genome, and is usually lost within a few cell divisions.

However, the smaller chromosome carries so few essential genes that its loss is usually clinically insignificant.

[10] A Robertsonian translocation in balanced form results in no excess or deficit of genetic material and causes no health difficulties.

If, for example, the long arms of chromosomes 13 and 14 fuse, no significant genetic material is lost—and the person is completely normal in spite of the translocation.

[11] Most people with Robertsonian translocations have only 45 chromosomes in each of their cells, yet all essential genetic material is present, and they appear normal.

A Robertsonian translocation. The short arms of the chromosomes (shown on right) are often lost
Chromosome arms can have different length ratios. Robertsonian translocation occurs in acrocentric chromosome pairs (number II in the image), where the short arms are fairly short but not very short. A : Short arm (p arm)
B : Centromere
C : Long arm (q arm)
D : Sister chromatids
Human karyotype with annotated bands and sub-bands as used for the nomenclature of chromosome abnormalities. It shows dark and white regions as seen on G banding . Each row is vertically aligned at centromere level. It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes , as well as the mitochondrial genome (at bottom left).
Further information: Karyotype