Aneuploidy & chromosomal rearrangements
Aneuploidy: Extra or missing chromosomes
- Monosomy is when an organism has only one copy of a chromosome that should be present in two copies .
- Trisomy is when an organism has a third copy of a chromosome that should be present in two copies .
Nondisjunction of chromosomes
Genetic disorders caused by aneuploidy
- A duplication, where part of a chromosome is copied.
- A deletion, where part of a chromosome is removed.
- An inversion, where chromosomal region is flipped around so that it points in the opposite direction.Diagram schematically representing a deletion, duplication, and inversion.Deletion: a region of the original chromosome is removed, leading to a shorter chromosome missing a section.Duplication: a region of the original chromosome is duplicated, leading to a longer chromosome with an extra copy of a particular section.Inversion: a region of the original chromosome separates from the rest of the chromosome and is replaced in its original spot, but in the opposite orientation,
- A translocation, where a piece of one chromosome gets attached to another chromosome. A reciprocal translocation involves two chromosomes swapping segments; a non-reciprocal translocation means that a chunk of one chromosome moves to another.Diagram schematically representing reciprocal and non-reciprocal translocations.Reciprocal translocation: two non-homologous chromosomes swap fragments. No genetic material is lost, but the resulting chromosomes are hybrids, each containing segments normally found on a different chromosome.Non-reciprocal translocation: a fragment is removed from a donor chromosome and inserted into a recipient chromosome. The donor chromosome loses a region, while the recipient chromosome gains a region not normally found on that chromosome.