A marker chromosome is extra chromosomal material that cannot be clearly identified or characterised using conventional banding techniques.
It is actually a partial trisomy that originates from one or more of the 24 different chromosomes.
Marker chromosomes can be inherited (approximately 30%) or may arise de novo (approximately 70%).
The impact of a marker chromosome completely depends on its contents. If the marker chromosome mostly contains inactive genetic material, its effect will be minimal.
Often marker chromosomes are not inherited because they are small chromosomes and are therefore lost during cell division.
One of the marker chromosomes that occurs quite frequently is a reversed duplication of chromosome 15.